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Bacteria’s shape adapted to throat?


Andrew Fabich  We are so informed, at ScienceDaily:

Evolution moulds the shapes of living creatures according to the benefits they offer. At the microscopic level, do the various shapes of bacteria also contribute to their survival? Does a spherical bacterium (coccus) have a better chance of infecting its host than its stick-shaped neighbour (bacillus)?

Analysis of the evolution of the pathogenic bacteria that live in the nasopharynx suggests that the shape of these bacteria has changed over time, shifting from bacillus to coccus. In an article published in the journal PLOS Genetics, Professor Frédéric Veyrier, of INRS-Institut Armand-Frappier Research Centre, and his colleagues demonstrate that this change may have occurred to make the bacteria better at slipping through the defences of their host’s immune system.

Public health officials keep careful watch over respiratory infections, which are the number three cause of death worldwide. The pathogens responsible for these infections have evolved in order to thwart immune defences. Highly adapted to the ecological niche of nasal passages, Neisseria meningitidis and Moraxella catharralis can sometimes cause severe infections in humans. Genetic analysis of the ancestors of these bacteria pinpointed a key gene: yacF. The absence of this gene makes it possible for the shape of these bacteria to evolve. The N. meningitidis and M. catharralis found today in humans are spherical and missing the yacF gene. More.

Okay, maybe. But a reader, Andrew Fabich, Associate Professor of Microbiology at Liberty U, writes to say:

Utter hogwash. No one can explain a single reason why one of the myriad shapes of bacteria are selected for in the first place. Missing a gene isn’t exactly something observed for the first time. What I’d like to see is the explanation for all of the following (known) shapes: coccus (round), bacillus (rod), spirillum (spiral-shaped), spirochete (like a corkscrew), coccobacillus (yes, it’s a combination of the two other shapes), rectangles (yes, they even come with right angles), and (my ever favorite) star-shaped (no joke). Let alone the bacteria that are pleomorphic (aka shape changers, like some of your favorite comic book characters). Give me an evolutionary advantage for shape and I’ll begin to listen. This is a far cry from an evolutionary mechanism. Go back to writing honest news reports for better job security.

For the microbiology questions: Readers?

For the job security questions: In all honesty, much science writing today is just naturalist atheism dressed up in science gabble. And it sells. It makes people feel smart. It certainly doesn’t cause them to question whether they are in fact smart.

That has little to do with science as such. It’s more like, why aren’t the space aliens contacting us? (?) Or “Brit mid-market tabloid says Large Hadron Collider within days of discovering parallel universe.

And to think here at UD we missed out on that story! Oh wait, … Anyway, nothing’s gonna change. Here’s the abstract:

Respiratory infectious diseases are the third cause of worldwide death. The nasopharynx is the portal of entry and the ecological niche of many microorganisms, of which some are pathogenic to humans, such as Neisseria meningitidis and Moraxella catarrhalis. These microbes possess several surface structures that interact with the actors of the innate immune system. In our attempt to understand the past evolution of these bacteria and their adaption to the nasopharynx, we first studied differences in cell wall structure, one of the strongest immune-modulators. We were able to show that a modification of peptidoglycan (PG) composition (increased proportion of pentapeptides) and a cell shape change from rod to cocci had been selected for along the past evolution of N. meningitidis. Using genomic comparison across species, we correlated the emergence of the new cell shape (cocci) with the deletion, from the genome of N. meningitidis ancestor, of only one gene: yacF. Moreover, the reconstruction of this genetic deletion in a bacterium harboring the ancestral version of the locus together with the analysis of the PG structure, suggest that this gene is coordinating the transition from cell elongation to cell division. Accompanying the loss of yacF, the elongation machinery was also lost by several of the descendants leading to the change in the PG structure observed in N. meningitidis. Finally, the same evolution was observed for the ancestor of M. catarrhalis. This suggests a strong selection of these genetic events during the colonization of the nasopharynx. This selection may have been forced by the requirement of evolving permissive interaction with the immune system, the need to reduce the cellular surface exposed to immune attacks without reducing the intracellular storage capacity, or the necessity to better compete for adhesion to target cells. (Public access) – Frédéric J. Veyrier, Nicolas Biais, Pablo Morales, Nouria Belkacem, Cyril Guilhen, Sylvia Ranjeva, Odile Sismeiro, Gérard Péhau-Arnaudet, Eduardo P. Rocha, Catherine Werts, Muhamed-Kheir Taha, Ivo G. Boneca. Common Cell Shape Evolution of Two Nasopharyngeal Pathogens. PLOS Genetics, 2015; 11 (7): e1005338 DOI: 10.1371/journal.pgen.1005338

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For sure shape has an evolutionary advantage even if we are not quite sure of the details. There is a review by Kevin Young that explains all the advantages of the different shapes: http://mmbr.asm.org/content/70/3/660.short Each of these shapes have advantages and inconveniences. For example, the star shape increases the surface of interaction which can be good or bad depending on the ecosystem you live in. Pleomorphic Bacteria , as it is the case for Haemophillus influenzae another bacteria living in the nasopharynx that can be bacillus or coccus when found in the mucosa, may need to adapt the form because they live in different ecosystems or have different needs. Starbuck

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