What is the significance of horizontal gene transfer

This was an unexpected finding since almost half of that amount was the maximum known amount of possible HGT up to that moment. As bacteria have survived in difficult conditions for years, even decades, the researchers found that the acquisition of foreign DNA by other organisms also plays an important role in the high ability to withstand particular conditions Boothby et al.

Another interesting example demonstrating the role of HGT in the evolution of new traits was the recognition of mitochondria-deficient microorganisms.

It was commonly believed that all eukaryotic cells are required to have a mitochondrial organelle to survive, however, in with genome sequencing of an anaerobic eukaryotic microorganism, Monocercomonoides sp. Further analysis revealed that Monocercomonoides sp. Numerous studies demonstrate that the evolution of asexual reproduction in bdelloid rotifers has undergone HGT over the years in order to adapt to microenvironmental changes.

Horizontal gene acquisition is one of the ways to maintain intact genes in bdelloids. Bdelloid rotifers are microscopic multicellular animals that exist in aquatic environments. These microorganisms are resistant to harsh conditions and are even able to survive in a completely dry conditions lacking all water. Under these conditions, the double-stranded DNA breaks down, and, after exposure to enough water, foreign DNA is acquired horizontally from prokaryotes and even in some cases from other rotifers; in this manner, these microorganisms can repair their chromosomes.

Despite the occurrence of ameiotic reproduction in bdelloids, changes and diversity in genes and ramifications in the rotifer species are feasible through the phenomenon of HGT. Subtelomeric sequences of the bdelloids chromosomes indicate a high volume of external and non-metazoan genetic material. Moreover, the symbiosis of Planococcus citri mealybug and Tremblaya princeps, beside its endosymbiont, Moranella endobia is considered as a complex form of HGT. Since the Tremblaya has been affected by the degeneration process over years of evolution, its correlation with Moranella compensates for the lost genes which are mostly involved in essential amino acid synthesis and metabolic functions Husnik et al.

The way organisms can survive in arsenic-rich environments is a clear example of cross-kingdom HGT that enables extremophilic eukaryote to adapt to life, as it has horizontally received ArsM As III SAM methyltransferase form bacteria or archaea. Thus, the transfer and diffusion of arsM genes horizontally from bacteria to other kingdoms have made it possible to resist the toxicity of this metal.

It has been observed that in addition to the arsM genes that exhibit preserved S-adenosylmethionine-binding motifs to transport methyl to As III , three preserved cysteine residues of ArsM protein have also been detected in positions Cys72, Cys, and Cys in the thermophilic algae Cyanidioschyzon merolae sp. Likewise, Helicobacter pylori , the pathogenic gastric bacterium, uses the transition of nickel metal to enter and survive in the stomach. The common ancestor of H. Nickel is the cofactor for urease enzyme.

Urease generates carbon dioxide CO 2 and ammonia NH3 buffers via urea hydrolysis which can neutralize the acidic conditions of the stomach, and subsequently adapt bacteria to the gastric acidic environment Fischer F. Hypothenemus hampei , also known as a coffee berry borer, is a serious coffee pest that causes a lot of damage annually to the coffee industry around the world. The invasive beetle obtains this feature through the HhMAN1 gene gain from its gut bacteria.

The presence of antibiotic-resistant bacteria ARB or ARGs in the environment and their subsequent acquisition by clinically important microorganisms, such as plants, is a serious health-related issue. Soil fungi is shown to cause the transfer and distribution of bacteria in different parts of the soil. Naturally, fungi can spread over distances and can enrich bacteria by harboring cryptic- and nutrition-assisting plasmids in their mycosphere.

Subsequently, the wave of ARGs spread is formed in humans with uncontrolled use of antibiotics, and also via the food chain. Agrobacterium tumefaciens is a clear example of HGT from bacteria to eukaryotes. This Gram-negative bacterium is able to transfer and merge DNA into plant genomes, causing crown-gall disease. To this, the physical attachment of Agrobacterium to the cell wall of the plant is required to insert its T-DNA. This secretion system has the ability to spread the antibiotic resistance by the transfer of plasmids.

Later, this microorganism was exploited as a useful transfer system for genetic engineering. In this way, bacteria are capable of changing and evolving eukaryotes genomes mediated by HGT Fronzes et al.

As a subset of TEs, endogenous retroviruses ERVs have been integrated into the human genome by retroviral infections of the germline cells of our ancestors where, over a long period of evolutionary time, each REV is dispersed across the genome in hundreds to thousands of repetitive copies Wallau et al. Nonetheless, transcriptome analyses of somatic tissues surrounding tumor cells indicated co-expression of genes with TEs, extending the idea that transposon is expressed in both somatic and germ-line cells Chung et al.

Co-opted by the host during evolution and having the capability of self-duplication and mobilization, ERVs provide a massive pool of autonomous gene regulatory modules, indispensable for normal regulation of genes and gene networks. Examples include pmediated regulation Wang et al. Accordingly, besides their wide implication in normal gene regulation processes and their application as useful tools for genome editing and gene therapy purposes, on the dark side, the high rate of transposition rate Romanish et al.

They also adversely affect the prospect of stem cell-based therapies Schumann et al. In cancers, hypomethylation Ross et al. During onco-exaptation, silent TEs can be epigenetically reactivated to promote cancer. To date, analysis of the prevalence of TE onco-exaptation events across 7, tumors and normal datasets from 15 cancer types resulted in the identification of oncogenes out of TE cryptic promoter-activation events across 3, tumors. A study on genomic instability pathways arising from retrotransposon insertions in colorectal cancer CRC revealed highly variable retrotransposon activity among tumors and identified recurrent insertions in 15 known cancer genes.

Clinically, the high number of insertions are independently associated with poor disease-specific survival Cajuso et al. Human stem cells are indispensable for most basic, clinical, and translational research, such as gene therapy and regenerative medicine. However, they are wider in the clinic and are still limited by their potential risks due to genomic instability and tumorigenesis concerns Schumann et al.

Owing to their self non-self -mobilizing potential, ERs are used as genetic engineering toolkits to introduce foreign DNA transgene to desired genomic regions in target cells. Moreover, L1 has a role in the normal development of the embryo.

After fertilization, global chromatin accessibility at the beginning of development by L1 transcriptional activation is important for normal embryonic development Jachowicz et al. Also, the L1 RNA is required for repression of the transcriptional program specific to the 2-cell embryo and promotes exit from the 2-cell stage Percharde et al. Genotoxicity concerns for retrotransposon-mediated gene transfer are contradictory and reviewed in detail elsewhere Schumann et al.

Random L1 mobilization in our genome can result in numerous disorders. These disorders are caused by the mutagenic activity of non-LTR retrotransposons, with a rate of 1— pathogenic human mutations due to L1-mediated retrotransposition events. A complete list of ER-related human diseases can be found in Hancks and Kazazian Although specific TE-derived products can result in different consequences, there is a common pathogenic reaction, known as general inflammatory response.

In this section, we review the implication of newly emerged HGT tools adopted by eukaryotic cells to promote the emergence of beneficial traits as well as evolving numerous human-related maladies, in particular cancer. Plants, in particular parasitic plants, accept a large quantity of genes horizontally. In parasitic plants, such a genome exchange is partly due to the food dependency to their host. Parasitic plants penetrate the tissues of donor plants by their haustorium to intake nutrients along with their genetic material.

Thus, HGT monitoring will help to control the generation and function of parasitic plants, which is one of the most important agricultural problems in the world. DNA transferred horizontally can lead to the adaptive evolution of the recipient plants.

Results from transcriptome analysis of three parasitic members of Orobanchaceae Triphysaria versicolor , Striga hermonthica , and Phelipanche aegyptiaca and a non-parasitic member Lindenbergia showed 52 DNA non-sexual transfers between the parasite members of Orobanchaceae and their hosts. These data show that the greater dependence of parasitic plants on their hosts might increase the chance for HGT, and HGT occurs more significantly in heterotrophic plants than non-parasitic plants Yang et al.

Entering a large number of genes into the Amborella trichopoda mitochondrial genome by angiosperm, mosses and green algae as donors Rice et al. The issue of the transmittance of mitochondrial cytochrome c oxidase I COX1 group I introns into the Araceae family has already been investigated by Cusimano et al.

They demonstrated that fungi donate the introns into these flowering plants to promote the evolution of angiosperms. Similarly, phylogenetic studies demonstrate the distribution of the hAT superfamily DNA transposons horizontally between Drosophila species Schaack et al.

A paper by Ivancevic et al. Their research team traced and scrutinized these two foreign genes in a large number of eukaryotes genomes and showed evidence that they have identified for the first time the horizontal transmission in L1 elements.

Also, they stated that plenty of lateral BovB elements are transferred between various species Ivancevic et al. This is important as these events are actively involved in cancer progression and metastasis outbreak. In this section, we discuss the implication of HGT mediators including EVs exosomes , apoptotic bodies, and cfDNA in the emergence and progression of cancer, as well as the development of drug resistance. Evidence suggests that apoptotic cells derived from dying cells tumor cells can laterally transfer complex information to other cells, as they are shown to carry various cargoes including DNA, RNA, and protein.

Further, changes in the outer membrane of apoptotic cells can induce neighboring cells to become phagocytic de la Taille et al. The consequence of apoptotic-mediated information transfer is not always pathologic, as in the case of bone remodeling which occurs each 2-weeks, a large number of apoptotic bodies are produced by mature osteoclasts. Earlier experiments indicated that oncogenic DNA can be transferred to cells by phagocytosis of apoptotic bodies. Results showed that apoptotic bodies derived from EBV-carrying B lymphocytes when cocultured with other cells e.

Thus, HGT mediated by apoptotic cells can be a route for infection of cells that lack the receptor for the virus Holmgren et al. A similar experiment is reported where DNA coding for the ARGs hygr-r can be transferred by apoptotic prostate cells to the Neomycin-resistant and bcl-2 overexpressing LNCaP prostate cells resulting in dual-antibiotic resistant prostate cancer cell clones de la Taille et al.

Uptake of apoptotic bodies derived from H-rasV and human c-myc-transfected rat fibroblasts by pnegative murine phagocytic cells results in loss of contact inhibition in vitro , aneuploidy, and the accumulation of the genetic changes that spark tumor formation in vivo Bergsmedh et al. Further studies indicated that besides DNase II, the activity of Chk2, p53, and p21 signaling pathways can counteract propagation of apoptotic bodies-derived oncogenic DNA, thus it forms a genetic block against transformation and malignant phenotype Bergsmedh et al.

Besides apoptotic bodies, cfDNA is another precious tool with an implication in diagnosis, prognosis, and monitoring of cancer. Also, larger DNA up to 10, bp with a necrotic cell origin is detected in cancer patients Jahr et al. Various experiments have documented the oncogenic potential of cfDNA on normal cells. Thus, recipient cell genetic alteration with the potential to derive tumorigenicity and development of tumors are among the most serious subjects related to HDT Trejo-Becerril et al.

Viral DNA integration into the human genome is an accepted fact, however, new studies indicated integration of bacterial DNA into the human somatic genome. This observation has now prompted a new hypothesis that the origin of cancer cells are bacteria. It equally questions the source of primary cancer cells PCCs and secondary metastatic cancer cells SCCs which are proposed to be originated from the senescent normal cells and cancer cells, respectively.

This observation suggests bacteria as the mighty origin of cancer cells Dong and Xing, Additionally, there is clinical evidence that bacterial DNA integrates into the human somatic genome through an RNA intermediate, as insertion of Acinetobacter and Pseudomonas genetic materials into human genome by HGT is validated which is causative to the development of acute myeloid leukemia AML and stomach adenocarcinoma, respectively Riley et al.

Also, data analysis of public cancer genome sequence data confirmed an association between the presence of mycobacterium tuberculosis complex in the glioblastoma multiforme GBM and ovarian serous cystadenocarcinoma OV samples, as well as the presence of Ralstonia spp.

One of the most critical factors in tumor formation and development is mitochondrial respiration affecting the effective extension of metastasis. Notably, the results of the conducted studies in this field point to the fact that tumor cells receive horizontally the mtDNA from other cells of the body to improve the cellular respiration conditions Berridge et al.

Cargo can be integrated on the outer or inner layer of the vesicle phospholipid membrane through anchoring proteins or can be packed inside the vesicle. Besides normal cells, apoptotic cell-derived extracellular vesicles ApoEVs are also described as containing nuclear materials and mitochondria and presenting cell-specific markers on the surface, which enable tracking of the cell of origin Jiang et al.

Interestingly, EVs are shown to mediate the horizontal transfer and integration of RNA intermediates into the human genome. To this, human cancer cells were transfected with an expression construct containing a retrotransposition-competent human L1 tagged with a reporter gene. Further analysis of isolated EVs showed enrichment of L1-derived reporter RNA transcripts from cancer cells expressing active L1 retrotransposition Kawamura et al.

Discovering the tumor-derived exosomes in cancerous mice revealed the releasing of epidermal growth factor receptor EGFR in host macrophages which cause a decrease in interferon-1 gene expression, and thereby the immune response is reduced against viral infection Gao et al. Thus, tumor cells can transfer activated EGFR through EVs to the host macrophage to dampen innate immunity response, rendering the host immunocompromised. Initial experiments validating genomic DNA transfer of a model gene by exosomes comes from the study in which a lentiviral vector encoding Arabidopsis thaliana-DNA A.

Further quantification and verification of PCR-products from the recipient cell suggested stable integration of A. Complex exchange of genetic information is evidenced in the pathogenesis of cancer.

Likewise, microRNA-containing EVs derived from the sera of patients with colorectal cancer as well as HT29 colon cancer cells can induce the transformation of fibroblasts into colon carcinoma cells Abdouh et al. In this view, a therapeutic strategy can be envisioned by targeting cancer-derived EVs. Finally, depletion of EVs, as evidenced by their preferential internalization by macrophages, was capable of reducing metastatic burden in a human breast cancer xenograft mouse model Nishida-Aoki et al.

As EVs are present in all fluids of living animals, exosome-mediated HGT is the driving force behind mammalian genome evolution which can be translated into cancer development as well as adaptation and drug resistance Baghban et al.

Engineered exosomes that display tumor-specific targeting receptors e. In an interesting study, metastatic-Trap m-tarp was manufactured using exosomes embedded on a three-dimensional platform as a trap favorable secondary site to lure metastatic cells.

For this, exosomes purified from the ascitic fluid of ovarian cancer patients were validated as intermediaries of tumor cell attachment. Transplantation of the device into the peritoneal cavity of mice resulted in the capturing of ovarian metastatic cells and significantly improved survival outcomes by disrupting the crosstalk between metastatic cells and their environment de la Fuente et al.

On the bright side, the potential of exosomes as natural and non-toxic agents vectors to induce long-term changes in the receipt cells was further translated into the gene therapy as an alternative to the time-consuming and laborious gene cloning as well as for targeted functionalized exosomes and controlled drug delivery. Indeed, the evidence for HGT related to the transfer of mitochondria has changed the previously accepted paradigms regarding the role of anaerobic glycolysis in cancer cell metabolism.

Although glycolytic metabolism is recognized as the key hallmark of many cancer cells, tumor cells also need oxidative phosphorylation OXPHOS to meet their pathophysiological demands. On the contrary to the previous fact suggested by Warburg that defects in mitochondria are causative to cancer initiation, some cancer cells retain OXPHOS capacity with no clear respiratory defects Frezza and Gottlieb, ; Jose et al.

Respiration is key for cancer cell formation, proliferation, progression, and metastasis Viale et al. Surprisingly, cancer cells deprived of mtDNA can restore their respiration potential through a rare phenomenon which is regulated by HGT involving the transfer not of mtDNA but of whole mitochondria Tan et al. Results from an invaluable study revealed that mtDNA-deficient tumor display delays in tumor formation potential compared to their normal counterpart.

It also showed that progression was associated with respiration recovery and acquiring mtDNA from the host. Further studies showed that efficient tumor formation, recovery of mitochondrial respiration, and mtDNA acquisition occurs via trafficking of whole mitochondria between mammalian cells in vivo Dong et al.

As a therapeutic strategy, mitochondria transplantation is demonstrated to improve antitumor activity and reduce chemoresistance and mitochondrial dynamics in breast cancer in vitro Chang et al. Since the genetic remodeling of a single organism is not enough to meet this requirement, HGT has emerged as an effective approach to provide such a survival advantage.

The appearance of phenotypic changes can be immediate e. Horizontal gene transfer acts as a double-edged sword: although it fuels innovation and diversity in nature, now, its effects function against the survival benefit in nature, especially in humans. For one, the dawn of the post-antibiotic area is highly predicted as a consequence of HGT in the future, at a time point in which the bacteria will no longer respond to antibiotics. Equally, in the context of other diseases, such as cancer, HGT not only promotes the development of the clonal population of cells capable of tumorgenesis, it also sparks tumor cell heterogeneity and the emergence of multi-drug resistance Dianat-Moghadam et al.

Such survival advantage to tumors is mediated, partly, by the newly discovered HGT mediators in the eukaryotes. DNA from apparently dead tumor cells, called apoptotic bodies, can be transferred to living tumor cells, as naked, in complex with other biomaterials or being packed into the EVs.

Organotypic metastasis, which refers to the tendency of tumors to seed in selective and preferred organs, has recently been shown to be regulated by exosomes.

Indeed, the expression of specific surface receptors on exosomes is shown to prepare secondary organs for tumor metastasis. And that disrupting these interactions can selectively avoid metastatic outbreaks in several mice models Hoshino et al. Accordingly, the most important matter about HGT is to understand its transmission mechanism s , which, in turn, will provide many advantages and opportunities.

For example, instead of focusing on the development of new antibiotics, the horizontal transmission mechanism in bacteria will be considered as a therapeutic target.

Given that the process for the development of new antibiotics is time-consuming and expensive, disruption of HGT in bacteria populations, using, for example, the CRISPR-Cas9 system, can disconnect genetic exchange among bacteria. Thus, not only can the development of antibiotic drug resistance be prevented, but inter- and intra-species transmission of virulence factors can be reduced as well. This is of paramount importance given the ever-increasing cases of acquired resistance to a wide range of routinely- and clinically used antibiotics.

From another angle, a comprehensive understanding of HGT mediators will offer a great benefit to genetic engineering. Given the high costs and low efficiency of current gene therapy tools, recognition of HGT mechanisms can lead to the development of more efficient and cheaper gene therapy methods, for treatment of postnatal genetic diseases such as those related to a specific enzyme deficiency metabolic disorders or even for the treatment of cancer.

Thus, it can predict the recipient bacteria that will become resistant to specific antibiotics. As the target host is already predicted, a combination modality can be highly effective to monitor resistance to the newly introduced antibiotics in the clinic. Equally, machine learning can be applied for the prediction of mobile elements movement in the human genome.

Half of the human genome is composed of inserted sequences from other organisms, of which only transposons have the capability of jumping and transferring gene fragments in the eukaryotic DNA.

As the role of TEs is well established in the pathogenesis of multifactorial diseases, such as cancer and neurodegenerative disease, a machine learning approach can spot the next location of jumping elements in the human genome. Once the new jumping site is recognized, then one can predict the good or bad consequence of transposon insertion. Finally, the more recent clinically important mediators of HGT among eukaryotic cells are exosomes, cfDNA, and apoptotic bodies, through which distant cancer cells can communicate together.

Thus, it allows the clinicians to plan the most suitable drug regimens based on disease state and adopt a timely intervention to control the disease and achieve desirable therapeutic effects Baghban et al. Thus, horizontal transfer mediators may be the next generation point-of-care diagnostic, prognostic, and therapeutic tools to predict, cure, and prevent various human-related maladies, in particular cancer. All authors listed have made a substantial, direct and intellectual contribution to the work, and approved it for publication.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Abdouh, M. Colorectal cancer-derived extracellular vesicles induce transformation of fibroblasts into colon carcinoma cells.

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You can also search for this author in PubMed Google Scholar. Correspondence to Patrick J. Jeffrey D. Palmer's homepage. In a phylogeny, when a branching pattern cannot be resolved, the branches in question can be collapsed to show the absence of a hypothesis for the relationships among the lineages that they represent. A general eukaryotic cellular process using the cytoskeleton and endomembrane system to take up material from the environment.

An organism living in a symbiotic association with another, specifically by attachment to the surface of its host.

An organism living in a symbiotic association with another, specifically by living inside a host cell. A fermentative compartment of the digestive system in many cellulose-digesting vertebrates, the contents of which are rich in anaerobic protists and prokaryotes. A lineage of protists for example, Tetrahymena and Paramecium , predominantly predators, defined by the presence of dimorphic nuclei and large numbers of short flagella cilia on the surface.

They are members of the Chromalveolates. A lineage of protist flagellates for example, Trypanosoma, the sleeping-sickness agent , predominantly made up of parasites, and home to many unusual characteristics of genome structure for example, RNA editing. They are members of the Excavates. A lineage of anaerobic or microaerophic protist flagellates for example, Giardia lamblia , predominantly parasitic and often studied because of their reduced metabolism and mitochondria.

A lineage of anaerobic or microaerophic protist flagellates for example, Trichomonas , predominantly parasitic and often studied owing to their reduced metabolism and their hydrogenosome, a hydrogen-producing mitochondrial relict. A lineage of protist flagellates for example, Alexandrium, a red tide alga with photosynthetic, heterotrophic and parasitic representatives, which are known for many unusual modifications to genome structure — they are members of the Chromalveolates.

A lineage of protist parasites for example, Phytophthora, the potato late-blight agent that are responsible for numerous plant diseases, and were once mistakenly thought to be fungi but are really heterokonts. Feeding by absorption of nutrients directly from the environment which can include a host organism in the case of parasites.

A lineage of protist for example, oomycete parasites and kelps with photosynthetic, heterotrophic and parasitic representatives, all of which are united by the possession of uniquely dimorphic flagella.

A lineage of photosynthetic protist for example, Emiliania , predominantly marine, some of which form massive marine blooms, and many of which make distinctive calcium carbide scales that have contributed significantly to limestone deposits. A lineage of photosynthetic protist for example, Bigelowiella with amoeboid and flagellate life stages, best known for their retention of a relict nucleus of their green algal plastid endosymbiont, known as a nucleomorph.

They are members of the Rhizaria. In phylogeny, a common ancestor and all its descendants are monophyletic for example, animals , as opposed to a collection of organisms that does not include their common ancestor, which are polyphyletic for example, flying animals. Monophyletic is sometimes subdivided into holophyletic the most recent common ancestor and all things that evolved from it, for example, animals and paraphyletic the most recent common ancestor, but not all the things derived from it, for example, reptiles — from which birds evolved.

A hypothetical 'supergroup' of protists, including apicomplexa, dinoflagellates, ciliates, heterokonts, haptophytes and cryptomonads, all of which are hypothesized to have diverged from an ancient common ancestor that has acquired a plastid by secondary endosymbiosis with a red alga. Reprints and Permissions. Horizontal gene transfer in eukaryotic evolution.

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BMC Bioinformatics Scientific Reports Science China Life Sciences Journal of Mathematical Biology BMC Genomics Advanced search. Skip to main content Thank you for visiting nature. Key Points Horizontal gene transfer HGT; also known as lateral gene transfer is the non-sexual movement of genetic information between genomes. Abstract Horizontal gene transfer HGT; also known as lateral gene transfer has had an important role in eukaryotic genome evolution, but its importance is often overshadowed by the greater prevalence and our more advanced understanding of gene transfer in prokaryotes.

Access through your institution. Buy or subscribe. Rent or Buy article Get time limited or full article access on ReadCube. Figure 1: The major bifurcations and reticulations in eukaryotic evolution. Figure 2: You are what you eat, what you live on, what lives on you, and what lives in you. Figure 3: Different kinds of transfer and their effects on gene phylogeny.

References 1 Doolittle, W. Article Google Scholar 7 Lander, E. Google Scholar 11 Andersson, J. Article Google Scholar 13 Ragan, M. Google Scholar 19 Hoffmeister, M. Google Scholar 50 Doolittle, W. Google Scholar 73 Bachvaroff, T. Google Scholar Fast, N. Article Google Scholar de Grey, A. Article Google Scholar Burki, F. Acknowledgements The authors wish to thank numerous colleagues for supplying unpublished data and several of the photos in Figure 2 see the figure for photo credits.

Palmer Authors Patrick J. Keeling View author publications. View author publications. Supplementary information. Supplementary information S1 table Number of genes putatively acquired from prokaryotesa in heavily sequenced protists PDF kb.

Glossary Polytomy In a phylogeny, when a branching pattern cannot be resolved, the branches in question can be collapsed to show the absence of a hypothesis for the relationships among the lineages that they represent. Endocytosis A general eukaryotic cellular process using the cytoskeleton and endomembrane system to take up material from the environment. Ectosymbiont An organism living in a symbiotic association with another, specifically by attachment to the surface of its host.

Endosymbiont An organism living in a symbiotic association with another, specifically by living inside a host cell. Rumen A fermentative compartment of the digestive system in many cellulose-digesting vertebrates, the contents of which are rich in anaerobic protists and prokaryotes.

Ciliate A lineage of protists for example, Tetrahymena and Paramecium , predominantly predators, defined by the presence of dimorphic nuclei and large numbers of short flagella cilia on the surface. Trypanosomid A lineage of protist flagellates for example, Trypanosoma, the sleeping-sickness agent , predominantly made up of parasites, and home to many unusual characteristics of genome structure for example, RNA editing.

Diplomonad A lineage of anaerobic or microaerophic protist flagellates for example, Giardia lamblia , predominantly parasitic and often studied because of their reduced metabolism and mitochondria. Parabasalian A lineage of anaerobic or microaerophic protist flagellates for example, Trichomonas , predominantly parasitic and often studied owing to their reduced metabolism and their hydrogenosome, a hydrogen-producing mitochondrial relict.

Dinoflagellate A lineage of protist flagellates for example, Alexandrium, a red tide alga with photosynthetic, heterotrophic and parasitic representatives, which are known for many unusual modifications to genome structure — they are members of the Chromalveolates.

Oomycete A lineage of protist parasites for example, Phytophthora, the potato late-blight agent that are responsible for numerous plant diseases, and were once mistakenly thought to be fungi but are really heterokonts. Osmotrophy Feeding by absorption of nutrients directly from the environment which can include a host organism in the case of parasites. Heterokont A lineage of protist for example, oomycete parasites and kelps with photosynthetic, heterotrophic and parasitic representatives, all of which are united by the possession of uniquely dimorphic flagella.

Haptophyte A lineage of photosynthetic protist for example, Emiliania , predominantly marine, some of which form massive marine blooms, and many of which make distinctive calcium carbide scales that have contributed significantly to limestone deposits. Chlorarachniophyte A lineage of photosynthetic protist for example, Bigelowiella with amoeboid and flagellate life stages, best known for their retention of a relict nucleus of their green algal plastid endosymbiont, known as a nucleomorph.

Monophyly In phylogeny, a common ancestor and all its descendants are monophyletic for example, animals , as opposed to a collection of organisms that does not include their common ancestor, which are polyphyletic for example, flying animals. Transduction Transduction involves the transfer of a DNA fragment from one bacterium to another by a bacteriophage.

Step 1 : A bacteriophage adsorbs to a susceptible bacterium. Step 2 : The bacteriophage genome enters the bacterium.

The genome directs the bacterium's metabolic machinery to manufacture bacteriophage components and enzymes. Bacteriophage-coded enzymes will also breakup the bacterial chromosome. Step 3: Occasionally, a bacteriophage capsid mistakenly assembles around either a fragment of the donor bacterium's chromosome or around a plasmid instead of around a phage genome.

Step 4 : The bacteriophages are released as the bacterium is lysed. Note that one bacteriophage is carrying a fragment of the donor bacterium's DNA rather than a bacteriophage genome. Step 5: The bacteriophage carrying the donor bacterium's DNA adsorbs to a recipient bacterium. Step 6: The bacteriophage inserts the donor bacterium's DNA it is carrying into the recipient bacterium.

Step 1: A temperate bacteriophage adsorbs to a susceptible bacterium and injects its genome. Step 2: The bacteriophage inserts its genome into the bacterium's chromosome to become a prophage.

Step 3: Occasionally during spontaneous induction, the DNA is excised incorrectly and a small piece of the donor bacterium's DNA is picked up as part of the bacteriophage's genome in place of some of the bacteriophage DNA that remains in the bacterium's chromosome.

Step 4: As the bacteriophage replicates, the segment of bacterial DNA replicates as part of the bacteriophage's genome. Every bacteriophage now carries that segment of bacterial DNA.

Step 5: The bacteriophage adsorbs to a recipient bacterium and injects its genome. Step 6: The bacteriophage genome carrying the donor bacterial DNA inserts into the recipient bacterium's chromosome. Conjugation Genetic recombination in which there is a transfer of DNA from a living donor bacterium to a living recipient bacterium by cell-to-cell contact.

Mobilizable plasmids, that lack the tra genes for self-transmissibility but possess the oriT sequences for initiation of DNA transfer, may also be transferred by conjugation if the bacterium containing them also possesses a conjugative plasmid.

The tra genes of the conjugative plasmid enable a mating pair to form while the oriT quences of the mobilizable plasmid enables the DNA to move through the conjugative bridge. General mechanism of transfer of conjugative plasmids by conjugation in Gram-negative bacteria In Gram-negative bacteria, the first step in conjugation involves a conjugation pilus sex pilus or F pilus on the donor bacterium binding to a recipient bacterium lacking a conjugation pilus.

Step 1: In Gram-negative bacteria, the first step in conjugation involves a conjugation pilus sex pilus or F pilus on the donor bacterium binding to a recipient bacterium lacking a conjugation pilus. Step 2: Typically the conjugation pilus retracts or depolymerizes pulling the two bacteria together. Step 3: Using the rolling circle model of DNA replication, a nuclease breaks one strand of the plasmid DNA at the origin of transfer site oriT of the plasmid.

The nuclease also has helicase activity and unwinds the strand that is going to be transferred. Step 4: The nicked plasmid strand enters the recipient bacterium. Step 5: Both the donor and the recipient plasmid strands then make a complementary copy of themselves.

Step 6: Both bacteria now possess the conjugative plasmid and can make a conjugation pilus. Exercise: Think-Pair-Share Questions A strain of living Streptococcus pneumoniae that cannot make a capsule is injected into mice and has no adverse effect. This strain is then mixed with a culture of heat-killed Streptococcus pneumoniae that when alive was able to make a capsule and kill mice.

After a period of time, this mixture is injected into mice and kills them. In terms of horizontal gene transfer, describe what might account for this.

A gram-negative bacterium that was susceptible to most common antibiotics suddenly becomes resistant to several of them. It also appears to be spreading this resistance to others of its kind.

Describe the mechanism that most likely accounts for this. Summary Mutation is a modification of gene function within a bacterium and while it enables bacteria to adapt to new environments, it occurs relatively slowly.

Horizontal gene transfer enables bacteria to respond and adapt to their environment much more rapidly by acquiring large DNA sequences from another bacterium in a single transfer. Horizontal gene transfer is a process in which an organism transfers genetic material to another organism that is not its offspring. Mechanisms of bacterial horizontal gene transfer include transformation, transduction, and conjugation.

During transformation, a DNA fragment from a dead, degraded bacterium enters a competent recipient bacterium and is exchanged for a piece of DNA of the recipient. Transduction involves the transfer of either a chromosomal DNA fragment or a plasmid from one bacterium to another by a bacteriophage.