Quorum Sensing Regulates ‘swim-or-stick’ Lifestyle in the Phycosphere

Abstract

Originality-significance statementMotility and biofilm formation are processes regulated by quorum sensing (QS) in bacteria. Both functions are believed to play an important role in interactions between bacteria and phytoplankton. Here, we show that two bacterial symbionts from the microbial community associated with a ubiquitous diatom switch their motile lifestyle to attached cells while an opportunist bacterium from the same community is incapable of attachment, despite possessing the genetic machinery to do so. Further work indicated that the opportunist lacks QS signal synthases while the symbionts produce three QS signals, one of which is mainly responsible for regulating symbiont colonization of the diatom microenvironment. These findings suggest that QS regulates colonization of diatom surfaces and further work on these model systems will inform our understanding of particle aggregation and bacterial attachment to marine snow and how these processes influence the global carbon cycle.SummaryInteractions between phytoplankton and bacteria play major roles in global biogeochemical cycles and oceanic nutrient fluxes. These interactions occur in the microenvironment surrounding phytoplankton cells, known as the phycosphere. Bacteria in the phycosphere use either chemotaxis or attachment to benefit from algal excretions. Both processes are regulated by quorum sensing (QS), a cell-cell signaling mechanism that uses small infochemicals to coordinate bacterial gene expression. However, the role of QS in regulating bacterial attachment in the phycosphere is not clear. Here, we isolated a Sulfitobacter pseudonitzschiae F5 and a Phaeobacter sp. F10 belonging to the marine Roseobacter group and an Alteromonas macleodii F12 belonging to Alteromonadaceae, from the microbial community of the ubiquitous diatom Asterionellopsis glacialis. We show that only the Roseobacter group isolates (diatom symbionts) can attach to diatom transparent exopolymeric particles. Despite all three bacteria possessing genes involved in motility, chemotaxis, and attachment, only S. pseudonitzschiae F5 and Phaeobacter sp. F10 possessed complete QS systems and could synthesize QS signals. Using UHPLC-MS/MS, we identified three QS molecules produced by both bacteria of which only 3-oxo-C16:1-HSL strongly inhibited bacterial motility and stimulated attachment in the phycosphere. These findings suggest that QS signals enable colonization of the phycosphere by algal symbionts.

Inherent tendency of Synechococcus and heterotrophic bacteria for mutualism on long-term coexistence despite environmental interference

“…5C ). QS signaling molecule has been shown to alter the bacterial composition ( 28 ), and QS-QQ are known to regulate bacterial chemotaxis, biofilm formation, and adhesion to phytoplankton environment ( 29 ). With this potential for such a profound effect, the contribution of these genes to the shift in bacterial community composition and the reestablishment of mutualism within the coculture system cannot be denied.…”

More than just hitchhikers: a survey of bacterial communities associated with diatoms originating from marine reptiles

“…2015). Recent findings also show that bacterial symbionts use quorum sensing to promote biofilm formation and phycosphere colonization, while diatoms can directly modulate bacterial colonization and suppress the opportunist attachment via secondary metabolites such as azelaic acid and rosmarinic acid (a quorum sensing mimic) (Fei et al . 2020; Shibl et al .…”

“…2015; van Tol, Amin and Armbrust 2017), and sexual reproduction (Cirri, Vyverman and Pohnert 2018; Cirri et al . 2019), while diatoms can directly modulate the bacterial community via secondary metabolite production (Fei et al . 2020; Shibl et al .…”

A comprehensive review on the use of algal-bacterial systems for wastewater treatment with emphasis on nutrient and micropollutant removal

“…Bacterial movement and biofilm development are controlled by QS. For instance, Fei et al [ 83 ] have shown that the QS influences the colonization of diatom surfaces by the bacteria. The study evaluated the association of three bacterial symbionts – Phaeobacter sp.…”