Characterizing MarR Homologs That Mediate Bacterial Fitness and Survival

Abstract

Plant disease outbreaks are on the rise, threatening food security in many parts of the globe. To address these enormous challenges, new intervention strategies like bio-controls are being used as an important sustainable alternative to mitigate the negative effects of pathogens and increase the quality and productivity of agricultural crops. MarR family transcriptional regulators have been studied for their involvement in regulating bacterial virulence genes that help colonize plant hosts and therefore could serve as targets for biocontrol. The transcriptional regulator PecS, a member of the MarR family, is encoded by select bacterial pathogens and we show here that PecS controls a range of phenotypes associated with bacterial fitness. Using a strain of Agrobacterium fabrum in which pecS has been disrupted, we show here that PecS controls a range of phenotypes associated with bacterial fitness. PecS represses flagellar motility and chemotaxis, processes that are important for A. fabrum to reach plant wound sites. The pecS disruption strain reduces biofilm formation and anaerobic survival while increasing acyl homoserine lactone (AHL) production and resistance to reactive oxygen species (ROS). The production of AHL and resistance to ROS are anticipated to be especially important in the host environment. We also demonstrate that PecS is not involved in the induction of vir genes required for TDNA transfer to plant host. Our data thus suggest that PecS is required to mediate A. fabrum fitness during its transition from the rhizosphere to the plant host. Fusaric Acid (FA) is a toxic fungal metabolite produced by several Fusarium species as a non-specific phytotoxin that causes plant illness. The Burkholderia thailandensis fusR gene, encoding a MarR Transcriptional regulator, is part of an operon with a putative fusaric acid binding protein, and we show that FA induced a concentration-dependent increase in the expression of genes in the fusR operon, as well as a thermal shift in FusR of up to 6oC at 5 mM FA. Overall, this study elucidates the role of PecS and FusR, two MarR transcription factors in conferring bacterial fitness, and thus constituting potential targets for bio-control intervention.