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An oxidoreductase is involved in cercosporin degradation by the bacterium Xanthomonas campestris pv. zinniae.

ABSTRACT: The polyketide toxin cercosporin plays a key role in pathogenesis by fungal species of the genus Cercospora. The bacterium Xanthomonas campestris pv. zinniae is able to rapidly degrade this toxin. Growth of X. campestris pv. zinniae strains in cercosporin-containing medium leads to the breakdown of cercosporin and to the formation of xanosporic acid, a nontoxic breakdown product. Five non-cercosporin-degrading mutants of a strain that rapidly degrades cercosporin (XCZ-3) were generated by ethyl methanesulfonate mutagenesis and were then transformed with a genomic library from the wild-type strain. All five mutants were complemented with the same genomic clone, which encoded a putative transcriptional regulator and an oxidoreductase. Simultaneous expression of these two genes was necessary to complement the mutant phenotype. Sequence analysis of the mutants showed that all five mutants had point mutations in the oxidoreductase gene and no mutations in the regulator. Quantitative reverse transcription-PCR (RT-PCR) showed that the expression of both of these genes in the wild-type strain is upregulated after exposure to cercosporin. Both the oxidoreductase and transcriptional regulator genes were transformed into three non-cercosporin-degrading bacteria to determine if they are sufficient for cercosporin degradation. Quantitative RT-PCR analysis confirmed that the oxidoreductase was expressed in all transconjugants. However, none of the transconjugants were able to degrade cercosporin, suggesting that additional factors are required for cercosporin degradation. Further study of cercosporin degradation in X. campestris pv. zinniae may allow for the engineering of Cercospora-resistant plants by using a suite of genes.

SUBMITTER: Taylor TV

PROVIDER: S-EPMC1563685 | biostudies-literature | 2006 Sep

REPOSITORIES: biostudies-literature

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An oxidoreductase is involved in cercosporin degradation by the bacterium Xanthomonas campestris pv. zinniae.

Taylor Tanya V TV Mitchell Thomas K TK Daub Margaret E ME

Applied and environmental microbiology 20060901 9

The polyketide toxin cercosporin plays a key role in pathogenesis by fungal species of the genus Cercospora. The bacterium Xanthomonas campestris pv. zinniae is able to rapidly degrade this toxin. Growth of X. campestris pv. zinniae strains in cercosporin-containing medium leads to the breakdown of cercosporin and to the formation of xanosporic acid, a nontoxic breakdown product. Five non-cercosporin-degrading mutants of a strain that rapidly degrades cercosporin (XCZ-3) were generated by ethyl ...[more]

PMID: 16957231

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Project description:UnlabelledN-Acetylglucosamine (GlcNAc), the main component of chitin and a major constituent of bacterial peptidoglycan, is present only in trace amounts in plants, in contrast to the huge amount of various sugars that compose the polysaccharides of the plant cell wall. Thus, GlcNAc has not previously been considered a substrate exploited by phytopathogenic bacteria during plant infection. Xanthomonas campestris pv. campestris, the causal agent of black rot disease of Brassica plants, expresses a carbohydrate utilization system devoted to GlcNAc exploitation. In addition to genes involved in GlcNAc catabolism, this system codes for four TonB-dependent outer membrane transporters (TBDTs) and eight glycoside hydrolases. Expression of all these genes is under the control of GlcNAc. In vitro experiments showed that X. campestris pv. campestris exploits chitooligosaccharides, and there is indirect evidence that during the early stationary phase, X. campestris pv. campestris recycles bacterium-derived peptidoglycan/muropeptides. Results obtained also suggest that during plant infection and during growth in cabbage xylem sap, X. campestris pv. campestris encounters and metabolizes plant-derived GlcNAc-containing molecules. Specific TBDTs seem to be preferentially involved in the consumption of all these plant-, fungus- and bacterium-derived GlcNAc-containing molecules. This is the first evidence of GlcNAc consumption during infection by a phytopathogenic bacterium. Interestingly, N-glycans from plant N-glycosylated proteins are proposed to be substrates for glycoside hydrolases belonging to the X. campestris pv. campestris GlcNAc exploitation system. This observation extends the range of sources of GlcNAc metabolized by phytopathogenic bacteria during their life cycle.ImportanceDespite the central role of N-acetylglucosamine (GlcNAc) in nature, there is no evidence that phytopathogenic bacteria metabolize this compound during plant infection. Results obtained here suggest that Xanthomonas campestris pv. campestris, the causal agent of black rot disease on Brassica, encounters and metabolizes GlcNAc in planta and in vitro. Active and specific outer membrane transporters belonging to the TonB-dependent transporters family are proposed to import GlcNAc-containing complex molecules from the host, from the bacterium, and/or from the environment, and bacterial glycoside hydrolases induced by GlcNAc participate in their degradation. Our results extend the range of sources of GlcNAc metabolized by this phytopathogenic bacterium during its life cycle to include chitooligosaccharides that could originate from fungi or insects present in the plant environment, muropeptides leached during peptidoglycan recycling and bacterial lysis, and N-glycans from plant N-glycosylated proteins present in the plant cell wall as well as in xylem sap.

Dataset Information

An oxidoreductase is involved in cercosporin degradation by the bacterium Xanthomonas campestris pv. zinniae.

Publications

An oxidoreductase is involved in cercosporin degradation by the bacterium Xanthomonas campestris pv. zinniae.

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