A tandem GGDEF-EAL domain protein-regulated c-di-GMP signal contributes to spoilage-related activities of Shewanella baltica OS155

Cyclic diguanylate (c-di-GMP) is a second messenger involved in the regulation of various physiological processes in bacteria. However, its function in spoilage bacteria has not yet been addressed. Here, we studied the function of a tandem GGDEF-EAL domain protein, Sbal_3235, in the spoilage bacterium Shewanella baltica OS155. The deletion of sbal_3235 significantly reduced the c-di-GMP level, biofilm formation, and exopolysaccharide, trimethylamine (TMA), and putrescine production; sbal_3235 deletion also downregulated the expression of the torS and speF genes and affected membrane fatty acid composition. Site-directed mutagenesis in conserved GGDEF and EAL motifs abolished diguanylate cyclase (DGC) and phosphodiesterase (PDE) activity, respectively. These data indicate that Sbal_3235 is an essential contributor to the c-di-GMP pool with bifunctional DGC and PDE activity, which is involved in the biofilm formation and spoilage activity of S. baltica OS155. Our findings expand the biochemical role of c-di-GMP and uncover its link to spoilage activities, providing novel targets for food quality and safety controlling.