The AHL Quorum-Sensing System Negatively Regulates Growth and Autolysis in Lysobacter brunescens.

Jun Ling,Guichun Wu,Yancun Zhao,Tianping Jiang,Fengquan Liu,Lan Zhou

doi:10.3389/fmicb.2019.02748

Abstract

Lysobacter species are emerging as novel sources of antibiotics, but the regulation of their physiological metabolism is still poorly understood. In this work, we extracted AHL (acyl-homoserine lactone) autoinducers, identified the structures of AHLs and described the AHL quorum-sensing system in Lysobacter brunescens OH23. AHLs were isolated from the supernatant of L. brunescens OH23, and ESI-MS/MS (electrospray ionization mass spectrometry) analysis revealed biosynthesis of three different AHL chemical structures by L. brunescens OH23: N-(3-oxohexanoyl)- homoserine lactone (HSL), 3-OH-C10-HSL and C8-HSL. The growth rate of AHL quorum-sensing knockout mutants was dramatically increased compared to that of wildtype. Sucrose consumptions were also twice as high in AHL quorum-sensing knockout mutants than that in wildtype in early-log phase. Additionally, expression of key genes related to sucrose metabolism α-glucosidase was enhanced in AHL quorum-sensing knockout mutants, which indicated that AHL quorum sensing negatively regulates sucrose uptake and metabolism which further affects the growth rate of L. brunescens. Furthermore, autolysis was strongly induced in AHL quorum-sensing knockout mutants compared to wildtype, suggesting that AHL quorum sensing plays a negative regulatory role in cell autolysis. Moreover, compared to wildtype, XSAC (Xanthomonas-specific antibiotic compound) production was significantly increased in AHL knockout mutants in the early-log and late-log phases, and surface motility capabilities are also enhanced also in AHL knockout mutants; the normalized data of XSAC production and surface motility and expressions of key genes related to these two phenotypes reveal that growth rare and autolysis strongly affects XSAC biosynthesis and surface motility rather than AHL quorum-sensing system. Our results show that the AHL quorum-sensing system negatively regulates cell growth and autolysis, and further maintain nutrition homeostasis and population stability in L. brunescens.

Highlights

Lysobacter, belonging to Xanthomonadaceae, is a type of gramnegative bacteria that inhibits the growth of a variety of plant pathogens by producing various active secondary metabolites (Folman et al, 2003)
We report the role of the acyl-homoserine lactone (AHL) quorum-sensing system in the regulation of cell growth and autolysis, and our data revealed the sucrose consumption and autolysis system to be negatively regulated by the AHL quorum-sensing system
These findings indicate that the AHL quorum-sensing system negatively regulates sucrose consumption and that the growth rate is increased in AHL QS mutants compared to wildtype OH23

Summary

Introduction

Lysobacter, belonging to Xanthomonadaceae, is a type of gramnegative bacteria that inhibits the growth of a variety of plant pathogens by producing various active secondary metabolites (Folman et al, 2003). ATCC53042, inhibits a different pathogenic gram-positive and gram-negative bacteria (O’Sullivan et al, 1988). Campestris (Xcc), the diffusible signal factor (DSF) quorum-sensing system is widely distributed among gram-negative bacteria, Xanthomonas campestris and Xanthomonas oryzae (Barber et al, 1997; Wang et al, 2004). The DSF signaling molecule was identified as an unsaturated fatty acid with a chemical structure of cis-11-methyl-2-dodecenoic acid (Wang et al, 2004). It was discovered that Xcc can synthesize DSF molecules with at least three different structures, including DSF, cis-2-dodecenoic acid (BDSF) and [(2Z,5Z)-11-methyldodeca2,5-dienoci acid] (CDSF) (He et al, 2010). The structures of DSF signaling molecules vary, their biosynthesis in Xanthomonas is dependent on the gene cluster rpf (regulation of pathogenicity factor) (He et al, 2006). The perception and conduction of DSF signals is dependent on the two-component system RpfC/RpfG in bacteria, namely, the histidine kinase (HK) RpfC and response regulator (RR) RpfG; RpfC is responsible for the perception of signaling molecules and RpfG for signal transduction (Slater et al, 2000)

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Results

Conclusion