Cloning And Characterization Of A Solo Luxr In Lysobacter Enzymogenes OH11

Lysobacter enzymogenes is a ubiquitous plant-associated and environmental-friendly bacterium emerging as a novel biological control agent. A heat-stable antifungal factor (HSAF) is produced by Lysobacter enzymogenes in nutritionally limited conditions and. which exhibits strong activity against a wide range of fungi. The novel structure and mode of action has been characterized from this bacterium. The unique mechanism of HSAF biosynthesis also has been elucidated in our laboratory, however, the regulatory mechanism(s) of HSAF biosynthesis is largely unknown in L. enzymogenes. Luxl/R signal circuits regulate most gram-negative bacterial QS. A recent observation reveals that numerous sequenced proteobacterial genomes have QS-related LuxR AHL sensors but lack a cognate LuxI protein. These unpaired QS LuxR-family proteins have been called solos.In present study, we cloned a LuxR protein. LesR from L, enzymogenes strain OH11The primary structure of LesR consists of246amino acids; it possesses a typical AHL-binding domain at the N-terminus and a HTH DNA-binding domain at the C terminus, but is not directly associated with a cognate LuxI protein and hence it is a solo LuxR.Over expression, but not deletion of LesR significantly impaired HSAF biosynthesis level and antimicrobial activities, as well as accelerated cell aggregation and induced production of a melanin-like pigment in L. enzymogenes, and this melanin-like pigment was not associated with homogentisic acid. Further analysis showed that the cell aggregation and melanin-like pigment induced by LesR depend on DF (a quorum sensing signal molecule). Because overexpressing LesR in DF deletion mutant didn’t appear the melanin-like pigment and cell aggregation. Genetic analysis found that HSAF biosynthesis and cell aggregation regulated by LesR were related to the global transcriptional regulation factor Clp (cAMP-receptor like protein). What’s more, the C-terminus HTH binding-domain was critical for lesR-mediating functions. Proteomic analysis revealed that lesR influenced the expression of a wide range of proteins belonging to differentially functional groups. Overall, the study not only elucidated the roles of a solo LuxR protein in L. enzymogenes but also preliminary studied the regulatory mechanism of HSAF biosynthesis by LesR.