The lolB gene in Xanthomonas campestris pv. campestris is required for bacterial attachment, stress tolerance, and virulence

Abstract

Background Xanthomonas campestris pv. campestris (Xcc) is a Gram-negative bacterium that can cause black rot disease in crucifers. The lipoprotein outer membrane localization (Lol) system is involved in the lipoprotein sorting to the outer membrane. Although Xcc has a set of annotated lol genes, there is still little known about the physiological role in this phytopathogen. In this study, we aimed to characterize the role of LolB of Xcc in bacterial attachment, stress tolerance, and virulence. Results To characterize the role of LolB, lolB mutant was constructed and phenotypic evaluation was performed. The lolB mutant revealed reductions in bacterial attachment, extracellular enzyme production, and virulence. Mutation of lolB also resulted in reduced tolerance to a myriad of stresses, including heat and a range of membrane-perturbing agents. Trans-complementation of lolB mutant with intact lolB gene reverted these altered phenotypes to the wild-type levels. From subsequent reporter assay and reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) analysis, the expression of genes that encode the major extracellular enzymes and the stress-related proteins was reduced after lolB mutation. Conclusions The results in this work contribute to the functional understanding of lolB in Xanthomonas for the first time, and provide new insights into the function of lolB in bacteria.

Functional characterization and transcriptional analysis of degQ of Xanthomonas campestris pathovar campestris

“…Given that genes associated with attachment or biofilm in Xcc exhibit reduced virulence [12][13][14][15][43][44][45][46][47], we attempted to evaluate whether degQ is required for Xcc virulence. We demonstrated that degQ was required for full virulence (Figure 2).…”

Bacterial surface‐exposed lipoproteins and sortase‐mediated anchored cell surface proteins in plant infection

“…Some lipoproteins are part of cellular appendages such as flagella and pili (Jin et al, 2001), while others are integral components of the peptidoglycan biosynthesis machinery and transport systems for effectors, proteins, lipopolysaccharides, and antibiotics (Lorenz et al, 2019;Okuda & Tokuda, 2011). In some cases, lipoproteins are enzymes that have proteolytic and plant cell wall-degrading activities (Liao et al, 2022).…”

“…Some lipoproteins are part of cellular appendages such as flagella and pili (Jin et al, 2001 ), while others are integral components of the peptidoglycan biosynthesis machinery and transport systems for effectors, proteins, lipopolysaccharides, and antibiotics (Lorenz et al, 2019 ; Okuda & Tokuda, 2011 ). In some cases, lipoproteins are enzymes that have proteolytic and plant cell wall‐degrading activities (Liao et al, 2022 ). Besides the roles described for lipoproteins in model bacteria and human pathogens, phytopathogenic bacteria often rely on lipoproteins to attach to their preferred biological substrates, which is an important step in host colonization.…”

“…campestris mutant strain unable to produce LolB has pleiotropic phenotypes, ranging from decreased biofilm production to decreased virulence. LolB is required for the correct attachment of lipoproteins to the outer layer, so these symptoms could be explained by the general defect in cell membrane integrity and the perturbation of lipoprotein homeostasis (Liao et al, 2022 ). LolB is also required for in planta survival in the xylem‐invading phytopathogen Ralstonia solanacearum (Su et al, 2021 ).…”

LolA and LolB from the plant-pathogen Xanthomonas campestris forms a stable heterodimeric complex in the absence of lipoprotein

“…The importance of LolA and LolB in Xcc has been studied using transposon mutagenesis to generate lolA - ( Liao et al, 2019 ) and lolB -deficient ( Liao et al, 2022 ) Xcc mutant strains. In both cases, the effect of the mutant Xcc strains on cabbage was evaluated with similar results: substantial reduction in virulence, reduced pathogenicity, reduced bacterial attachment on abiotic surfaces and host leaves, significantly reduced production of extracellular enzymes, and greatly impaired stress tolerance.…”