In Sinorhizobium meliloti, the nodG gene is located in the nodFEG operon of the symbiotic plasmid. Although strong sequence similarity (53% amino acid identities) between S. meliloti NodG and Escherichia coli FabG was reported in 1992, it has not been determined whether S. meliloti NodG plays a role in fatty acid synthesis. We report that expression of S. meliloti NodG restores the growth of the E. coli fabG temperature sensitive mutant CL104 under non-permissive conditions. Using in vitro assays we demonstrated that NodG is able to catalyze the reduction of the 3-oxoacyl-ACP intermediates in E. coli fatty acid synthetic reaction. Moreover, although deletion of the S. meliloti nodG gene does not cause any growth defects, upon overexpression of nodG from a plasmid, the S. meliloti fabG gene, encoding the canonical 3-oxoacyl-ACP reductase, can be disrupted without any effects on growth or fatty acid composition. This indicates that S. meliloti nodG encodes a 3-oxoacyl-ACP reductase, and can play a role in f...

Walnut bacterial blight caused by Xanthomonas arboricola pv. juglandis ( Xaj) is one of the most prevalent diseases of walnut ( Juglans spp.), causing significant reductions in nut yield and important losses in economy. Enoyl-acyl carrier protein (ACP) reductase (ENR) is one of the key enzymes involved in the biosynthesis of bacterial fatty acids. In this study, we identified a single ENR-encoding gene, RS10040, in the genome of the XajDW3F3 strain. Sequence alignment analysis suggested RS10040 as a candidate fabV gene in Xaj. Expression of XajfabV restored the growth of the Escherichia coli fabI temperature-sensitive mutant under a nonpermissive growth condition. In vitro assays demonstrated that XajFabV catalyzed enoyl-ACPs of various chain lengths to acyl-ACPs, demonstrating its role in de novo fatty acid biosynthesis. Furthermore, we confirmed that XajfabV is an essential gene for growth, as no XajfabV deletion mutant could be obtained, although XajfabV in the chromosome could be deleted after compensating with a functional ENR-encoding gene via an exogenous plasmid. The fabV replacement mutants showed similar growth characteristic and fatty acid compositions. Our data further identified that fabV conferred Xaj with tolerance to various environmental stresses. Although XajFabV conferred Xaj with triclosan resistance, the resistance of Xaj was weaker than that found for Pseudomonas aeruginosa. Moreover, triclosan exhibited a control effect against infection of the Δ fabV/EcfabI to its host walnut. This study revealed the function of XajFabV and laid a theoretical foundation for the fatty acid synthesis mechanism of Xaj.

Diffusible signal factor (DSF) family signals represent a unique group of quorum sensing (QS) chemicals that modulate a wide range of behaviors for bacteria to adapt to different environments. However, whether DSF-mediated QS signaling acts as a public language to regulate the behavior of biocontrol and pathogenic bacteria remains unknown. In this study, we present groundbreaking evidence demonstrating that RpfF_Xc1 or RpfF_OH11 could be a conserved DSF-family signal synthase in Xanthomonas campestris or Lysobacter enzymogenes. Interestingly, we found that both RpfF_OH11 and RpfF_Xc1 have the ability to synthesize DSF and BDSF signaling molecules. DSF and BDSF positively regulate the biosynthesis of an antifungal factor (heat-stable antifungal factor, HSAF) in L. enzymogenes. Finally, we show that RpfF_Xc1 and RpfF_OH11 have similar functions in regulating HSAF production in L. enzymogenes, as well as the virulence, synthesis of virulence factors, biofilm formation, and extracellular polysaccharide production in X. campestris. These findings reveal a previously uncharacterized mechanism of DSF-mediated regulation in both biocontrol and pathogenic bacteria.