The YmdB protein regulates biofilm formation dependent on the repressor SinR in Bacillus cereus 0-9.

YmdB, which can regulate biofilm formation independently, has been reported to exist in Bacillus subtilis. The B. cereus 0-9 genome also encodes a YmdB-like protein, which has measureable phosphodiesterase activity, and 72.35% sequence identity to YmdB protein of B. subtilis 168. In this work, we studied the function of YmdB protein and its encoding gene, ymdB, in B. cereus 0-9. Our results indicated that YmdB protein is critical for the biofilm formation of B. cereus 0-9. In ΔymdB mutant, the transcriptional levels of sinR and hag were up-regulated, and those of genes closely related to biofilm formation, such as sipW, tasA and calY, were down-regulated. Deletion of ymdB gene stimulates the swarming motility of B. cereus 0-9, and enhances it to travel outward, but reduces its ability to form complex spatial structures on the solid surface of MSgg plates. Hence, it is considered that YmdB plays a key role in biofilm formation, and this effect is likely achieved through the function of repressor SinR in B. cereus 0-9. Furthermore, by comparing the amino acid sequences of YmdB by Basic Local Alignment Search Tool (BLAST) in Genebank, we found that YmdB homologues are present in a variety of bacteria (Including Gram-negative bacteria) except B. subtilis and B. cereus. All these bacteria come at different evolutionary distances and belong to different genera. Therefore, we believe that YmdB exists in many types of bacteria and plays an important role in the stress-resistance of bacteria to adapt to the environment. These results can help us to further understand the biocontrol characteristics of B. cereus 0-9.