Characterization and regulatory functions of PdeB, a protein containing both GGDEF and EAL domains in Vibrio parahaemolyticus.

Vibrio parahaemolyticus is a significant pathogen associated with seafood-borne illnesses in humans. C-di-GMP modulates various physiological functions such as motility, virulence, and biofilm development. In this study, characterize a c-di-GMP phosphodiesterase and identify a novel protein, PdeB, which contains both GGDEF and EAL domains and regulates motility and biofilm formation. PdeB enhances swarming by regulating lateral flagella expression. Intriguingly, although PdeB operates as a phosphodiesterase, its activity depends not only on the EAL domain but also requires the synergistic action of both the GGDEF and EAL domains. Furthermore, specific amino acid residues within the GGDEF domain are critical for PdeB's enzymatic function. Under conditions of elevated c-di-GMP resulting from scrABC knockout, PdeB is crucial in controlling swarming motility. It suppresses the transcription of vpa1446 and vpa1403, which are involved in the synthesis of extracellular polysaccharides, thus inhibiting biofilm biosynthesis. Additionally, transcriptomic sequencing further reveals that PdeB significantly influences physiological processes, with notable differential expression of flagellar-related and biofilm regulatory genes under liquid versus surface conditions. Additionally, PdeB gene expression is modulated through quorum sensing. This investigation broadens the understanding of c-di-GMP metabolic enzyme regulatory functions in V. parahaemolyticus, offering insights into the regulatory implications of c-di-GMP within bacterium.