2 research outputs found
Pantoea ananatis carotenoid production confers toxoflavin tolerance and is regulated by Hfqâcontrolled quorum sensing
Abstract Carotenoids are widely used in functional foods, cosmetics, and health supplements, and their importance and scope of use are continuously expanding. Here, we characterized carotenoid biosynthetic genes of the plantâpathogenic bacterium Pantoea ananatis, which carries a carotenoid biosynthetic gene cluster (including crtE, X, Y, I, B, and Z) on a plasmid. Reverse transcriptionâpolymerase chain reaction (RTâPCR) analysis revealed that the crtEXYIB gene cluster is transcribed as a single transcript and crtZ is independently transcribed in the opposite direction. Using splicing by overlap extension with polymerase chain reaction (SOE by PCR) based on asymmetric amplification, we reassembled crtEâB, crtEâBâI, and crtEâBâIâY. Highâperformance liquid chromatography confirmed that Escherichia coli expressing the reassembled crtEâB, crtEâBâI, and crtEâBâIâY operons produced phytoene, lycopene, and βâcarotene, respectively. We found that the carotenoids conferred tolerance to UV radiation and toxoflavin. Pantoea ananatis shares rice environments with the toxoflavin producer Burkholderia glumae and is considered to be the first reported example of producing and using carotenoids to withstand toxoflavin. We confirmed that carotenoid production by P. ananatis depends on RpoS, which is positively regulated by Hfq/ArcZ and negatively regulated by ClpP, similar to an important regulatory network of E. coli (HfqArcZ âRpoS Í° ClpXP). We also demonstrated that Hfqâcontrolled quorum signaling deârepresses EanR to activate RpoS, thereby initiating carotenoid production. Survival genes such as those responsible for the production of carotenoids of the plantâpathogenic P. ananatis must be expressed promptly to overcome stressful environments and compete with other microorganisms. This mechanism is likely maintained by a brake with excellent performance, such as EanR