Horizontal Gene Transfer and Antibiotic Resistance: A Study on Vibrio Cholerae

This article discusses the phenomenon of Horizontal Gene Transfer (HGT) and its role in antibiotic resistance, with a focus on Vibrio Cholerae. The study explores the complex process of transformation and the Type VI secretion system (T6SS) in HGT, and how it contributes to the dissemination of antibiotic-resistant genes. The findings shed light on our understanding of the movement of antibiotic resistance and the need for further research in this field.

Running head: HORIZONTAL GENE TRANSFER 1
Horizontal Gene Transfer
Name
Institution

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What the investigators did
In the article titled ‘’ Dial “V’’ for Murder by Christoph, the author emphasizes the
unusual and unexpected phenomenon of Horizontal Gene Transfer (Christoph, 2018). The author
discussed Horizontal Gene Transfer by transformation, which is the process of DNA uptake from
the environment. It is important to know that in transformation, fragments of DNA from
degraded and dead bacterium finds its way into a competent recipient bacterium and gets
exchanged for a piece of DNA of the recipient. It usually includes only homologous
recombination, which involves similar strains of bacteria from the same species of bacteria.
The author considered various several students that had been previously conducted in
detail on Bacillus subtilis, Haemophilus influenzae, Neisseria, gonorrhoeae and Streptococcus
pneumoniae. However, the author focused on Vibrio Cholerae to discuss his ideas and concepts
of how horizontal gene transfer takes place in what he terms as ‘a crime movie par excellence.’
The author discussed natural competence and transformation in the first basement followed by
Type VI secretion systems (T6SS). The author unfolded the ideas of the whole concepts in the
form of the movie in a screenplay.
What they tested
In the basement of the first take, the author discussed how horizontal gene transfer by
transformation is complex just like phage transduction or conjugation. It is important to note that
in both cases, Gram-negative and Gram-positive bacteria; horizontal gene transfer requires an
action that is coordinated of about two dozen organized genes with multiple operons. This same
case takes place in Vibrio cholerae. The author discussed that the model for competence, which

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includes 19+ genes, which has main components that include a type IV pilus (Tfp), a periplasmic
protein which binds nonspecifically to the double-stranded DNA and the inner membrane-bound.
The author discussed how the transformation of cholerae takes place in the nutshell. They
also discussed how the uptake of DNA begins with the retraction of the Tfp pilus and how it is
pulled via the pore of the outer membrane. However, in cholerae, transformation, they found two
key missing details that could unfold their crime story. The author, therefore, sought to find out
by testing the missing details of cholerae transformation briefly.
The author tested how one Vibrio predator and three-prey cell acted on each other after
getting in touch with each other. The experiment was carried out in 120 minutes, where they
were expected to elongate and divide until or unless they were destroyed. The killer Vibrio was
recognized by its faith green GFP fluorescence and the predators were recognized by their red
fluorescence of ComEA-mCherry, which was distributed in its periplasm.
The also wanted to demonstrate how the integration of transferred genes into the
chromosomes of the killer. Furthermore, they wanted to prove horizontal gene transfer by
demonstrating the recombination of some of its DNA into one of the two chromosomes of Vibrio
Cholerae as well as its subsequent expression. The authors, therefore, co-cultured a T6SS
proficient Vibrio Cholerae O1EI Tor A1552 which was predator strain with a prey that was a
deficiency T6SS and nonimmune Vibrio Cholerae chromosomes.
What they found out.
In the investigation, the author found out that the synthesis of the transformation
apparatus was energetically costly. It was found out that the effective way in which the synthesis
would be triggered was through the provision of conditions where exogenous DNA would

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potentially be available where biofilms were provided as an example of this conditions. Vibrios
in their aqueous natural habitats colonizes the carapaces of the crustaceans. After sensing chitin,
which is the main macromolecule element of the shells of the crustaceans, Vibrios degrade in
order to earn their living. They make the biofilm by being attached to it. According to Meibom
(2005) signal integration from the limitation of nutrients, chitin sensing and sensing of cell
density in the formation of biofilm, triggers the key regulator responsible for competence
expression called Tfox. On its own, Tfox elicits full competence within elevated density when it
is expressed from a promoter that is inducible.
In Bacteroidetes and Proteobacteria armory, it was found out that Type VI secretion
system could be easily spotted. It was found out that T6SS was not a long-range weapon. The
author found that it worked only at shorter distances especially when the cells are closer to each
other. On the contrary, to the phage particles tails, the inner tube does not provide DNA via it but
utilizes an effector delivery. The Vibrio Cholerae’T6SS is multi-protein complex that consists of
more than 20 components that comprise of membrane anchors, inner tube, sheath, effector
proteins and autoimmunity factors that are required for the protection against harming itself or its
siblings. They have normally organized clusters of three with one on the main chromosome I and
two on chromosome II.
In the experiment, it was found that Induced T6SS led to the destruction of its
surrounding cells followed by horizontal gene transfer. At 0 minutes, the action began and after
30 minutes the first victim had been lysed and stabbed. It became invisible to the surrounding
after its GFP fluorescence was diluted. At 60 minutes, they were blown out to a bleb forming a
protoplast because of the disintegration of the peptidoglycan that presided lysis. At the 90
minutes, the potential victims were no longer available and the killer Vibrio kept wielding its

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T6SS along with the intake of the deceased`s DNA. The killer had doubled in the filming process
and had already begun dividing at the 120 minutes. It was noted that the victim had been stabbed
before the 90 minutes. This experiment depicted how T6SS destroyed its surrounding cells
followed by horizontal gene transfer.
In the co-cultured proficient T6SS Vibrio cholerae and deficient T6SS Vibrio Cholerae it
was found that proficient Vibrio Cholerae had acquired the aph gene through homologous
recombination from its prey which was the deficient Vibrio Cholerae. The experimental
transformation indicated how horizontal gene transfer of a chromosomal resistance marker of the
antibiotic took place.
However, the author found out that that the T6SS mediated destruction of its neighboring
cells, as well as acquisition by horizontal gene, was not confined to the Vibrios. Cooper et al had
earlier demonstrated that the proficient T6SS and transformation competent Acinetobacter bablyi
destroyed the cells of the co-cultured E. Coli and thus acquired their resistance genes of
antibiotics. It was found that horizontal gene transfer took place at high frequency in few hours
under specific environmental conditions. It was also depicted that the cells of the newly resistant
A. babyli displayed antibiotic-sensitive kin when placed under conditions of selective growth.
What it means in our understanding of the movement of antibiotic resistance
The findings helped in solving the riddle of how the isolation of human pathogen
Acinetobacter baumanii in clinics accumulate several resistance genes of antibiotics. This has
shone a light in our understanding of the movement of antibiotic resistance. It is worth to note
that A. babyli is a bacterium that is found in the soil, therefore, the regulation of competence and
expression of T6SS is likely to differ considerably from that of a human pathogen. Several

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studies have been carried out on the same subject which fosters our knowledge of better
comprehension of the mechanism that leads to the re-emergence of human pathogens. It is
important to note that antibiotic resistance takes place when an antibiotic loses its ability to kill
or control the growth of bacteria effectively thus leading to further multiplication of bacteria
despite the presence of the therapeutic levels of an antibiotic.
Our understanding has been further fostered through antimicrobial resistance, which has
taught us more about horizontal gene transfer. HGT as demonstrated how it is responsible in the
dissemination of multiple determinants of antimicrobial-resistance throughout the diverse species
of bacteria. It is worth knowing that the author of the article utilized the Vibrio cholera bacteria
to demonstrate how transformation plays a role in antibiotic resistance. In this case, we become
aware of how of how V.cholerae becomes resistant to drugs by exporting drugs via chromosomal
mutations, efflux pumps and how they develop genetic resistance through the exchange of
conjugative transposons, conjugative plasmids and integrons. Another good example that
demonstrates how horizontal gene transfer fosters our understanding of antibiotic resistance is
through the bacteria Staphylococcus aureus. This pathogen is opportunistically responsible for
diverse infectious diseases that range from superficial skin abscesses and food poisoning to
infections that are more serious such as toxic shock syndrome, endocarditis, septicemia,
osteomyelitis, meningitis, and pneumonia (Cafini, Romero, Morikawa, 2017). Horizontal gene
transfer provides an explanation as to why this pathogen has become more resistant to drugs.
Horizontal gene transfer also fosters our understanding of this antibiotic resistance
especially from the way the author of this article has perfectly demonstrated (Galtier, 2007). The
article has indicated how horizontal gene transfer contributes to the spreading of antibiotic
resistance via the exchange of genetic material across various general, which elevates the

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potential for a harmful development of antibiotic-resistant bacteria. The major genetic
mechanisms of horizontal gene transfer especially transformation and conjugation have been
perfectly depicted how they contribute to the elevated frequencies of resistant genes for
antibiotics due to gene transfer and acquisition between various species.
Horizontal gene transfer as a topic on its own has depicted how naked DNA in
transformation is taken up by bacteria from an environment and incorporated into the genome
(Burmeister, 2015). Personally, this topic has transformed my knowledge and understanding of
antibiotic resistant. I feel the urge to continue venturing in this field of microbiology and in
future be able to take part in researching the effective techniques we can utilize as
microbiologists to beat up this global concern especially in clinical settings. However, this topic
urges scientists to continue doing more and advanced research in antibiotic resistance by
formulating drugs that can solve this global issue of antibiotic resistance. Transformation
together with transduction is capable of transferring a wide range of sequences that includes
resistant cassettes of antibiotics. By fostering our knowledge and understanding of antibiotic
resistance, further research can now be carried out to determine the effective way to formulate
drugs that are cannot be affected by resistance. Also, it makes us aware of the possible causes of
antibiotic resistance, and human behaviors that can initiate or contribute to antibiotic resistance
such as skipping of drugs that allows the antibiotic which increases antibiotic resistance. Most
importantly, transformation with other methods of horizontal gene transfer is essential for cell
adaptation, speciation, and cellular evolution. They both aids in the transfer of DNA from one
organism to another to elevate virulence and improve the efficacy of metabolic reactions.

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References
Burmeister AR. Horizontal Gene Transfer: Figure 1. Evolution, Medicine, and Public Health.
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Cafini F, Romero VM, Morikawa K. Mechanisms of Horizontal Gene Transfer. The Rise of
Virulence and Antibiotic Resistance in Staphylococcus aureus. 2017 Aug.
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Dial "V" for Murder. Small Things Considered. [accessed 2018 Nov 24].
http://schaechter.asmblog.org/schaechter/2018/01/dial-v-for-murder.html
Galtier N. A Model of Horizontal Gene Transfer and the Bacterial Phylogeny Problem.
Systematic Biology. 2007;56(4):633–642. doi:10.1080/10635150701546231
Meibom KL. Chitin Induces Natural Competence in Vibrio cholerae. Science.
2005;310(5755):1824–1827. doi:10.1126/science.1120096