How quorum sensing regulates bacterial colonization of the phycosphere
Involved team members: Cong Fei, Michael Ochsenkühn, Ahmed Shibl
Quorum sensing (QS) is one of the best-studied signaling mechanisms that bacteria use to communicate. QS regulates gene expression in response to fluctuations in cell-population density. Many bacteria carry out QS by secreting small signaling molecules, known as autoinducers. In Proteobacteria, the primary class of autoinducers is acyl-homoserine lactones (AHLs), which are synthesized by an autoinducer synthase (luxI) and perceived by an autoinducer regulator (luxR). Bacteria use AHLs to regulate functions that are beneficial to carry out collectively, such as virulence, motility, and biofilm formation.
QS is hypothesized to be important in the phycosphere, where quorum sensing bacteria can divide and build up a relatively high concentration of autoinducers. Previously, we have shown that two diatom symbionts that belong to the Roseobacter group use AHLs to inhibit their motility and enhance biofilm formation. In contrast, an opportunist bacterium, Alteromonas macleodii was incapable of adhering to diatom-generated transparent exopolymer particles and was found to lack the ability to synthesize AHLs. The ability of symbionts to switch their lifestyle from motile bacteria entering the phycosphere to permanent residents of this microenvironment is essential to successfully colonizing the phycosphere. This ‘swim-or-stick’ switch also appears to be partially controlled by diatoms that can make quorum sensing mimics, such as rosmarinic acid.
Currently, we are further examining the role of AHLs in the phycosphere by performing a scarless knockout of the luxI gene of diatom symbionts to comprehensively profile the effect of luxI on the function and metabolism of symbionts and further demonstrate the impact of AHLs on bacterial-algal interactions.
Plain English Summary
Like language in human societies, bacteria also use a common language to communicate. Bacterial communication relies on versatile chemical signaling molecules called autoinducers, which regulate bacterial gene expression in a process known as quorum sensing. Using these autoinducers, bacteria are able to count how many of them exist in the environment and accordingly change their behavior to collectively coordinate their responses to their environment. This process occurs in many environments, including the minute environment surrounding diatom cells, where diatom microbiomes reside. We are using a variety of molecular biology and genomics methods to study how these communication mechanisms enable bacteria to colonize this small microenvironment and thus influence diatom growth. These microbial interactions play an essential role in the oceans and shedding light on how they occur will enable us to predict the effects of climate change on these microbes.
C. Fei, M.A. Ochsenkühn, A.A. Shibl, S.A. Amin (2020). Quorum sensing regulates ‘swim-or-stick’ lifestyle in the phycosphere. Environ. Microbiol. 22, 4761-4778.