Reconstitution of a Biofilm Adhesin System from a Sulfate-Reducing Bacterium in Pseudomonas fluorescens

Biofilms of the sulfate reducing bacterium (SRB) Desulfovibrio vulgaris Hildenborough (DvH) can facilitate metal corrosion in various industrial and environmental settings leading to substantial economic losses; however, the mechanisms of biofilm formation by DvH are not yet well-understood. Evidence suggests that a large adhesin, DvhA, may be contributing to biofilm formation in DvH. The dvhA gene and its neighbors encode proteins that resemble the Lap system, which regulates biofilm formation by Pseudomonas fluorescens, including a LapG-like protease DvhG and effector protein DvhD, which has key differences from the previously described LapD. By expressing the Lap-like adhesion components of DvH in P. fluorescens, our data support the model that the N-terminal fragment of the large adhesin DvhA serves as an adhesin "retention module" and is the target of the DvhG/DvhD regulatory module, thereby controlling cell-surface location of the adhesin. By heterologously expressing the DvhG/DvhD-like proteins in a P. fluorescens background lacking native regulation ({Delta}lapG{Delta}lapD) we also show that cell surface regulation of the adhesin is dependent upon the intracellular levels of c-di-GMP. This study provides insight into the key players responsible for biofilm formation by DvH, thereby expanding our understanding of Lap-like systems. SignificanceCorrosion leads to [~]2.5 trillion US dollars in economic losses, 20% of which are estimated to be microbially induced. Biofilms of sulfate reducing bacteria (SRB), especially the genus Desulfovibrio, are important members of the corrosion consortium and accelerate deterioration of metals. Understanding how biofilms are formed by SRB can provide important clues to mitigate this challenge. In this study, we used genetic and biochemical tools to investigate the mechanism of biofilm formation by Desulfovibrio vulgaris Hildenborough. Our study reveals critical genes responsible for regulating the secretion of a large adhesin known to be required for biofilm formation.