Mutagenesis of PhaR, a Regulator Gene of Polyhydroxyalkanoate Biosynthesis of Xanthomonas oryzae pv. oryzae Caused Pleiotropic Phenotype Changes

Abstract

Polyhydroxyalkanoates (PHAs) are intracellular carbon and energy storage materials produced in various microorganisms under nutrient-limited conditions. PhaR is a regulatory protein involved in PHA synthesis. Xanthomonas oryzae pv. oryzae (Xoo) is one of the most important bacterial pathogens in rice and has PHA biosynthesis genes in its genome, but the biological function of phaR in Xoo is unknown. In this study, we investigated the effects of the mutagenesis of phaR gene in Xoo strain PXO99A. Compared to the wildtype, the PhaR gene knock-out mutant PXO99ΔphaR was hypermotile and showed decreased growth rates in both rich and limited nutrient media. PXO99ΔphaR also showed almost 75% decrease in extracellular polysaccharide (EPS) production. When inoculated in rice leaves by leaf-clipping method, PXO99ΔphaR displayed reduced virulence in terms of lesion length and bacterial multiplication compared with the wildtype strain. PXO99ΔphaR also showed enhanced hypersensitive response (HR) induction in the leaves of non-host Nicotiana benthamiana with elevated hpa1 gene expression. Introduction of a cosmid containing the phaR coding sequence restored the phenotypes of the mutant to those of the wildtype strain. These results suggest that PhaR gene is an important gene that affects multiple bacterial characteristics, including EPS production, growth rate, defense response induced harpin production and motility, related to its virulence in plant.

Bacterial biopolymers: from pathogenesis to advanced materials

“…In the plantpathogen Xanthomonas oryzae pv. oryzae, which causes major losses in rice production, the regulatory protein PhaR not only represses PHA synthesis but also affects production of extracellular polymeric substances, the bacterial life style, phenotypic changes and virulence 55 . PHAs are pro posed as a sink for electrons under anaerobic conditions; that is, in the absence of terminal electron acceptors such as oxygen, they enhance survival 56,57 ( Fig.…”

“…1). PHA synthe sis and mobilization are regulated in response to environ mental stimuli, such as nutritional and environmental stresses, providing a survival advantage 55 . PHAs have been considered as unique biobased plas tics that can be bioengineered, chemically modified and processed into highvalue medical materials (for example, sutures, tissue engineering scaffolds, drug carriers and (TAblE 1).…”

Polyhydroxyalkanoates (PHAs): Biopolymers for Biofuel and Biorefineries

“…Industry focused on two polyesters: polylactic acid (PLA) and PHAs, where PLA is economical and available in bulk but PHAs are expensive. However, the applications and properties of PHAs can be tailored by varying the co-monomer and the content of the copolyesters [ 26 , 27 , 28 , 29 ]. The advantages and disadvantages of both PLA and PHAs are compiled in Table 1 .…”

Bacterial Biopolymer: Its Role in Pathogenesis to Effective Biomaterials

“…PHA − mutants of P. aeruginosa reveal decreased attachment to surfaces of glass and diminished stress tolerance in presence of biofilms, therefore revealing a significant contribution of PHA in persistence in infections [ 37 ]. In one of the plant pathogens Xanthomonas oryzae (causes major rice production losses), the regulatory protein called PhaR represses the synthesis of PHA and also suppresses EPS production, thus affecting virulence and phenotypic changes modifying lifestyle of the bacteria [ 38 ]. PHAs are reported to be electron sinks, which in anaerobic conditions (terminal electron or oxygen absence) enhance survival [ 38 ].…”