Shayan Ahmed, Jamia Millia Islamia, New Delhi
Bacterial capsules:
For centuries bacteria have colonised nearly every corner of Earth, displaying an incredible capacity to adapt to diverse habitats and situations. The bacterial capsule, a polysaccharide-coated outer shell that surrounds the cells of many distinct bacterial species, is one important bacterial adaptation. Bacterial capsules function as a protective cocoon for bacteria, shielding them from harmful chemicals and desiccation while helping them to cling to surfaces and evade the host’s immune system. As a fact, bacterial capsules play a key role in virulence, and certain capsular types are closely linked to virulent human pathogenic strains. Horizontal Gene Transfer (HGT) is a mechanism in which bacteria acquire mobile genetic elements (MGEs) with specific properties that fuel their evolution.
What is horizontal gene transfer?
One of the hallmarks of bacterial evolution is the horizontal transfer of mobile DNA. MGEs are specialised vectors that can transmit DNA from one bacterial cell to another. Bacteriophages and conjugative plasmids are two of the most important forms of MGE. Conjugative plasmids are tiny circular DNA molecules that may move from one cell to another via a plasmid-encoded channel. For example, conjugative plasmids are the primary vehicle for the spread of antibiotic resistance genes among bacterial pathogens, posing a serious danger to public health. The bacterial capsule, as a thick exterior coat, acts as a natural barrier to plasmid and phage transmission. The capsule is known to protect bacteria against phage infection by concealing the surface receptors that phages employ for invasion. Pathogens’ evolutionary success is thus dependent on phages, plasmids, and capsules.
The recent study of interest:
In a recent study, Haudiquet and colleagues at Institut Pasteur in Paris combined in silico and in vitro approaches and suggested a paradigm for explaining the interaction of capsules, phages, and plasmids. They worked on opportunistic pathogen Klebsiella pneumoniae and established that non-capsulated K. pneumoniae clones are more likely than capsulated ones to accept conjugative plasmids. The researchers identified a delicate interaction between phages, plasmids, and K. pneumoniae, which resulted in capsule switching via an intermediate and self-limiting non-capsulated state. According to the findings, both capsule inactivation and/or capsule exchange are associated with an increase in MGE acquisition in K. pneumoniae lineages. The researchers offer a compelling explanation for both the mechanical foundation and the self-limiting character of this rapid rise in permissiveness to mobile DNA. It’s tempting to think that the increased influx of novel MGE throughout time represents a significant potential for bacterial evolution.
By using generalised, specialised, and lateral transduction, phages may easily transfer DNA across bacteria of the same capsular type. Aside from the genes necessary for their life cycle, phages can encode a small number of accessory genes that may be beneficial to the bacteria they infect. Furthermore, phages frequently transfer bacterial chromosome fragments that can be incorporated into the receiving bacteria’s chromosomal DNA and provides scope for bacterial evolution. However, given phage’s strong capsular specificity, one could anticipate phage-mediated access to new DNA to decline with time, as most DNA transfers would take place between genetically identical organisms. Capsule trading, on the other hand, results in an immediate boost in access to fresh MGE.
Significance of the study:
The findings of Haudiquet and colleagues offer up fresh and intriguing research paths. This study emphasises the necessity of taking into account the combined impact of several forms of MGE while investigating HGT. The influence of various MGE’s host range on their possible impacts on bacterial evolution is also highlighted in this study. The study in discussion as well as new research in this field will definitely contribute to a better understanding of how MGE interactions influence bacterial evolution.
Also read: A study on mRNA Vaccines: One Vaccine for all?
Reference:
- Santos-López, A., Rodríguez-Beltrán, J., & San Millán, Á. (2021). The bacterial capsule is a gatekeeper for mobile DNA. PLoS biology, 19(7), e3001308. https://doi.org/10.1371/journal.pbio.3001308
Author info:
Shayan Ahmed is currently pursuing a Master of Science degree in Microbiology from the Department of Biosciences, Jamia Millia Islamia, New Delhi. His area of research interest lies in antibiotic resistance and associated molecular mechanisms. His recent work was focused on understanding colistin resistance patterns in the environment, particularly in water bodies.
Some of his other publications are:
- https://bioxone.in/news/worldnews/endometrial-cancer-treatment-via-adjuvant-radiotherapy/
- https://bioxone.in/news/worldnews/paediatric-myasthenia-gravis-and-gut-microbiome/
- https://bioxone.in/news/worldnews/airborne-pollen-hypothesized-as-ideal-covid-19-carrier/
- The Corrosion Prediction from the Corrosion Product Performance
- Nitrogen Resilience in Waterlogged Soybean plants
- Cell Senescence in Type II Diabetes: Therapeutic Potential
- Transgene-Free Canker-Resistant Citrus sinensis with Cas12/RNP
- AI Literacy in Early Childhood Education: Challenges and Opportunities
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