Lsp family proteins regulate antibiotic biosynthesis in Lysobacter enzymogenes OH11

Ax21 family proteins have been shown to play regulatory roles in plant- and animal-pathogenic species in the bacterial family Xanthomonadaceae, but the protein have not been investigated previously in the non-pathogenic members of this bacterial family. Lysobacter enzymogenes, is a non-pathogenic species known for its capacity as a biocontrol agent of plant pathogens. It is also noted for the production of antimicrobial secondary metabolites, heat stable antifungal factor (HSAF) and WAP-8294A2, that have potential for agricultural and pharmaceutical applications. The species also displays type IV pili-dependent twitching motility and the production of multiple extracellular lytic enzymes as additional biocontrol-related traits. Here, we show that L. enzymogenes strain OH11 possesses three genes widely separated in the OH11 genome that code for unique Ax21-like proteins (Lsp). By comparing the wildtype OH11 with mutant strains having a single lsp gene or a combination of lsp genes deleted, we found that each Lsp protein individually is involved in positive regulation of HSAF and WAP-8294A2 biosynthesis, but the proteins collectively do not exert additive effects in this regulation. None of the Lsp proteins were found to influence twitching motility or the production of three extracellular lytic enzymes. This study is the first to provide evidence linking Ax21-family proteins to antibiotic biosynthesis and, hence, adds new insights into the diversity of regulatory functions of Ax21 family proteins in bacteria.