Sodium Lactate Negatively Regulates Shewanella putrefaciens CN32 Biofilm Formation via a Three-Component Regulatory System (LrbS-LrbA-LrbR)

The capability of biofilm formation has a major impact on the industrial and biotechnological applications of Shewanella putrefaciens CN32. However, the detailed regulatory mechanisms underlying biofilm formation in S. putrefaciens CN32 remain largely unknown. In the present study, we describe a three-component regulatory system which negatively regulates the biofilm formation of S. putrefaciens CN32. The three-component regulatory system consists of a histidine kinase LrbS (Sputcn32_0303) and two cognate response regulators including a transcription factor LrbA (Sputcn32_0304) and a phosphodiesterase LrbR (Sputcn32_0305). LrbS responds to the signal of carbon source sodium lactate and subsequently activates one cognate response regulator LrbA. The activated LrbA then promotes the expression of the other response regulator gene lrbR . The c-di-GMP phosphodiesterase LrbR, containing an EAL domain, decreases the concentration of intracellular c-di-GMP, thereby negatively regulating biofilm formation. In summary, carbon source sodium lactate acts as a signal molecule that regulates biofilm formation via a three-component regulatory system (LrbS/A/R) in S. putrefaciens CN32. IMPORTANCE Biofilm formation is a significant capability for bacteria to survive in adverse environments. Numerous environmental factors can affect biofilm formation through different signal transduction pathways. Carbon source is one of the critical nutrients for bacterial growth, and its concentrations and types significantly influence the biomass and structure of biofilms. However, the underlying mechanism of biofilm formation regulated by carbon source is still limited. This work elucidates a modulation pattern of biofilm formation negatively regulated by a carbon source of sodium lactate via a three-component regulatory system in S. putrefaciens CN32, which may serve as a good example for studying how the carbon sources impact the biofilm development in other bacteria.