Abstract
Microbial biofilms associated with marine particulate organic matter carry out transformations that influence local and regional biogeochemical cycles. Early microbial colonizers are often hypothesized to “set the stage” for biofilm structure, dynamics, and function via N-acyl homoserine lactone (AHL)-mediated quorum sensing (QS). Production of AHLs, as well as antimicrobials, contributes to the colonization success of members of the Roseobacter clade. One member of this group of abundant marine bacteria, Rhodobacterales sp. Y4I, possesses two QS systems, phaRI (QS1) and pgaRI (QS2). Here, we characterize mutants in both QS systems to provide genetic evidence that the two systems work in hierarchical fashion to coordinate production of the antimicrobial indigoidine as well as biofilm formation. A mutation in pgaR (QS2) results in decreased expression of genes encoding both QS systems as well as those governing the biosynthesis of indigoidine. In contrast, mutations in QS1 did not significantly influence gene expression of QS2. Addition of exogenous AHLs to QS1 and QS2 mutants led to partial restoration of indigoidine production (45–60% of WT) for QS1 but not QS2. Mutational disruptions of QS1 had a more pronounced effect on biofilm development than those in QS2. Finally, we demonstrate that c-di-GMP levels are altered in QS and indigoidine biosynthesis Y4I mutants. Together, these results indicate that pgaRI (QS2) is at the top of a regulatory hierarchy governing indigoidine biosynthesis and that the global regulatory metabolite, c-di-GMP, is likely integrated into the QS circuitry of this strain. These findings provide mechanistic understanding of physiological processes that are important in elucidating factors driving competitiveness of Roseobacters in nature.
Original language | English |
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Article number | 681551 |
Journal | Frontiers in Marine Science |
Volume | 8 |
DOIs | |
State | Published - Jul 5 2021 |
Externally published | Yes |
Funding
This work was funded by the National Science Foundation (OCE-1357242 to AB). The authors would like to thank the Campagna Lab (UTK), specifically Amanda May and Ashley Lato, for their help with AHL detection and analysis. For assistance with experimentation, the authors acknowledge Jillian Walton. For their contributions to the discussion and scope of this manuscript, the authors acknowledge Sarah Lebeis, Karen Lloyd, Gladys Alexandre, and Nathan Cude. The authors would also like to thank Katherine M. Fullerton for editorial comments. Funding. This work was funded by the National Science Foundation (OCE-1357242 to AB).
Keywords
- AHLs
- Roseobacter clade bacteria
- biofilm
- cyclic-di-GMP
- quorum sensing