The posttranscriptional regulator CsrA affects multidrug resistance and biocontrol activity in Lysobacter enzymogenes

The posttranscriptional regulator CsrA regulates many cellular processes, including stress responses in diverse bacteria. However, the role of CsrA in multidrug resistance (MDR) and biocontrol activity in Lysobacter enzymogenes strain C3 (LeC3) remains unknown. In this study, we demonstrated that deletion of the csrA gene resulted in the initial slow growth of LeC3 and reduced its resistance to multiple antibiotics, including nalidixic acid (NAL), rifampicin (RIF), kanamycin (Km), and nitrofurantoin (NIT). Loss of the csrA gene also reduced its ability in inhibiting hypha growth of Sclerotium sclerotiorum and influenced its extracellular cellulase and protease activities. Two putative small noncoding regulatory RNAs (sRNAs), referred to as csrB and csrC, were also revealed in the genome of LeC3. Double deletion of csrB and csrC in LeC3 led to increased resistance to NAL, RIF, Km, and NIT. However, no difference was observed between LeC3 and the csrB/csrC double mutant in their suppression of S. sclerotiorum hypha growth and production of extracellular enzymes. These results suggest that CsrA in LeC3 not only conferred its intrinsic MDR, but also contributed to its biocontrol activity.