Sigma factor RpoN employs a dual transcriptional regulation for controlling twitching motility and biofilm formation in Lysobacter enzymogenes OH11.

Lysobacter is a Gram-negative genus comprising a group of environmental bacteria with abilities to produce abundant novel antibiotics, as well as adopting a unique type IV pilus (T4P)-mediated twitching motility (TM) that remains poorly understood. Here, we employ L. enzymogenes OH11 exhibiting significant antifungal activity as a working model to address this issue. Via mutating the 28 potential sigma factors in strain OH11, we have identified one protein RpoN (sigma 54) that is indispensable for T4P formation and TM. We further showed that RpoN not only regulates the transcription of pilA, but also another crucial gene chpA that encodes a hybrid two-component transduction system. The L. enzymogenes RpoN was found to directly bind to the promoter of chpA to control its transcription, which is found to be essential for the T4P-mediated TM. To our knowledge, such a transcriptional regulation performed by RpoN in control of bacterial TM has never been reported. Finally, we showed that L. enzymogenes OH11 could also produce biofilm that is likely employed by this strain to infect fungal pathogens. Mutation of rpoN , pilA and chpA all led to a significant decrease in biofilm formation, suggesting that the dual transcriptional regulation of pilA and chpA by RpoN plays a key role for RpoN to modulate the biofilm formation in L. enzymogenes. Overall, this study identified chpA as a new target of RpoN for controlling the T4P-mediated twitching motility and biofilm formation in L. enzymogenes OH11.