Abstract
BackgroundXanthomonas 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.ResultsTo 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.ConclusionsThe 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.
Highlights
Xanthomonas campestris pv. campestris (Xcc) is a Gram-negative bacterium that can cause black rot disease in crucifers
Bacterial lipoproteins are a set of membrane proteins localized on either leaflet of the lipid bilayer and are important components of the Gram-negative cell envelope [2, 3]
In Escherichia coli, most lipoproteins are considered to be anchored to the inner leaflet of the outer membrane [3, 4]
Summary
Xanthomonas campestris pv. campestris (Xcc) is a Gram-negative bacterium that can cause black rot disease in crucifers. Bacterial lipoproteins are a set of membrane proteins localized on either leaflet of the lipid bilayer and are important components of the Gram-negative cell envelope [2, 3]. In Escherichia coli, most lipoproteins are considered to be anchored to the inner leaflet of the outer membrane [3, 4]. The Lol pathway has components in each compartment of the cell envelope: an ATP binding cassette transporter LolCDE in the inner membrane; a soluble chaperone protein LolA in the periplasmic space; and a lipoprotein LolB in the outer membrane [4]. The outer membranedirected lipoprotein is extracted from the inner membrane by LolCDE, transferred to LolA, and shuttled to the outer membrane, where LolB receives and anchors them into the bilayer [2,3,4,5]. The Lol proteins of E. coli have been studied in depth and each of the lol genes are considered to be essential for viability of this bacterium [2, 3, 5]
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