Article in ISME Journal
Quorum sensing-regulated chitin metabolism provides grazing resistance to Vibrio cholerae biofilms
Eukaryote ecology has a rich body of established theory that is proving increasingly applicable to biofilm systems as microbial ecologists are taking advantage of the conceptual frameworks long established in ecology theory.
The concepts derived from the study of the interactions of higher organisms can provide a valuable tool for deciphering microbial interactions and begin to bridge the a gap in our understanding of ecologically relevant interactions within environmental biofilm communities.
One such example of the benefits derived from linking a biofilm system with eukarote ecology theory is Sun et al 2015. Here we provide a mechanistic explanation for the adaptive advantage of surface associated growth of Vibrio cholerae in the environment.
Vibrio cholerae is a natural inhabitant of the marine environment and its primary niche is the chitinous surfaces of zooplankton, especially copepods. V. cholerae can utilise chitin as a sole nutrient source and will up-regulate genes involved in horizontal gene transfer (HGT) when attached to chitin, making this niche an important one for acquisition of new genetic material.
Protozoa are a major mortality force for bacteria in the environment and because of this, bacteria have evolved many defence mechanisms. We have shown that for V. cholerae, biofilm formation is one of the protective mechanisms that allows cells to escape grazing pressure from predators such as the cosmopolitan surface feeder, Rhynchomonas nasuta (1).
This study shows that chitin metabolism is regulated by cell to cell communication, or quorum sensing (QS), and further elucidates a role for chitin metabolism in protection from predation by heterotrophic protists or protozoa (2). V. cholerae grown on chitinous surfaces and on Artemia are more toxic to the predator than biofilms grown on abiotic surfaces (plastic or glass). When the gene encoding the QS regulator, hapR was mutated, the chitin-grown biofilms were significantly less toxic. This toxicity was linked to the production of ammonia as a by-product of chitin catabolism.
The fact that biofilms of V. cholerae on chitinous surfaces are better protected than biofilms on abiotic surfaces may explain the adaptive advantage of attachment of V. cholerae to copepods.
This study demonstrates that biofilms can exhibit inducible defences that are due inpart to chemical cues released by the grazer. Further, the factors responsible for virulence may have evolved for some purpose other than virulence to host. As such virulence is a result of selection acting on the pathogen in a different environmental niche, thus supporting the coincidental evolution hypothesis.
1). Matz, C, D McDougald, AM Moreno, PY Yung, FH Yildiz, S Kjelleberg. 2005. Biofilm formation and phenotypic variation enhance predation-driven persistence of Vibrio cholerae. Proc Natl Acad Sci, USA 102:16819-16824.
2) Sun, S, QXM Tay, S Kjellberg, SA Rice, D McDougald. 2015. Quorum sensing-regulated chitin metabolism provides grazing resistance to Vibrio cholerae biofilms. ISME J. 9: 1812–1820
Read the article : http://www.nature.com/ismej/journal/v9/n8/full/ismej2014265a.html