Deciphering the functions of the outer membrane porin OprBXo involved in virulence, motility, exopolysaccharide production, biofilm formation and stress tolerance in Xanthomonas oryzae pv. oryzae

Abstract

Xanthomonas oryzae pv. oryzae (Xoo) is a Gram-negative bacterium causing bacterial leaf blight disease in rice. Previously, proteomic analysis has shown that the outer membrane protein B in Xoo (OprBXo) is more abundant in the wildtype strain than is the outer membrane protein 1 in the Xoo (Omp1X) knockout mutant. OprBXo shows high homology with OprB, which has been well characterized as a carbohydrate-selective porin in X. citri ssp. citri and Pseudomonas species. However, the functions of OprBXo in Xoo have not yet been documented. To elucidate the functions of OprBXo, we generated the OprBXo-overexpressing mutant, Xoo(OprBXo), and the knockout mutant, XooΔoprBXo(EV). We found that the virulence and migration of Xoo(OprBXo), but not XooΔoprBXo(EV), were markedly reduced in rice. To postulate the mechanisms affected by OprBXo, comparative proteomic analysis was performed. Based on the results of proteomics, we employed diverse phenotypic assays to characterize the functions of OprBXo. Abnormal twitching motility and reduction in swarming motility were observed in Xoo(OprBXo). Moreover, Xoo(OprBXo) decreased, but XooΔoprBXo(EV) enhanced, exopolysaccharide production and biofilm formation. The chemotactic ability of XooΔoprBXo(EV) was dramatically lower than that of Xoo(EV) in the presence of glucose and xylose. Xoo(OprBXo) was resistant to sodium dodecylsulphate and hydrogen peroxide, but XooΔoprBXo(EV) was highly sensitive compared with Xoo(EV). Thus, OprBXo is not only essential for chemotaxis and stress tolerance, but also for motility, biofilm formation and exopolysaccharide production, which may contribute to the virulence of Xoo. These results will lead to new insights into the functions of a sugar-selective porin in Xoo.

A LysR-Type Transcriptional Regulator LcrX Is Involved in Virulence, Biofilm Formation, Swimming Motility, Siderophore Secretion, and Growth in Sugar Sources in Xanthomonas axonopodis Pv. glycines

“…Exopolysaccharide (EPS) production was evaluated as previously described with slight modifications (Bae et al, 2018b). Xag strains were grown to an OD 600 of 0.1 in 5 ml XVM2 for 5 days at 28°C.…”

PXO_RS20535, Encoding a Novel Response Regulator, Is Required for Chemotactic Motility, Biofilm Formation, and Tolerance to Oxidative Stress in Xanthomonas oryzae pv. oryzae

“…Flagella-dependent motility is necessary during initial biofilm formation to identify and interact with an appropriate surface [ 35 ]. To understand the reduced motility and biofilm formation ability of RR35, we tested the transcriptional expression of fleQ ( PXO_RS11980 ), which is the master regulator in the gene expression associated with biosynthesis of a flagellum with alternative sigma factor RpoN2 [ 27 , 36 ]. As shown in Figure 6 , the transcriptional level of fleQ ( PXO_RS11980 ) decreased in the RR35 strain, suggesting that the expression of the master regulator of flagellar genes is influenced by RR35.…”

“…Chemotaxis of the RR35 strain was investigated on the surface of semisolid soft agar medium 0.3% without a carbon source, as previously reported with slight modification [ 27 ]. Briefly, Xoo strains were cultured in XOM2 broth medium in a shaking incubator at 28 °C to OD 600 = 3.5 × 10 8 CFU/mL, transferred to XOM2 fresh medium, and adjusted to OD 600 = 0.2.…”

Putative Bifunctional Chorismate Mutase/Prephenate Dehydratase Contributes to the Virulence of Acidovorax citrulli

“…In X. oryzae pv. oryzae , the knockout mutant of outer membrane porin, has irregular shape twitching motility and an alteration in stress tolerance ( Bae et al, 2018 ). Likewise, in this study, we showed that AcΔcmpAc (EV) reduced the production of twitching halo, which may contribute to the virulence of the group II Ac strain KACC17005.…”