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Rice bacterial blight pathogen Xanthomonas oryzae pv. oryzae produces multiple DSF-family signals in regulation of virulence factor production.

He YW, Wu J, Cha JS, Zhang LH - BMC Microbiol. (2010)

Bottom Line: Xoo produces a range of virulence factors, including EPS, extracellular enzyme, iron-chelating siderophores, and type III-secretion dependent effectors, which are collectively essential for virulence.All the three DSF-family signals promote EPS production and xylanase activity in Xoo, but CDSF is less active than its analogues DSF and BDSF.The composition and ratio of the three DSF-family signals produced by Xoo are influenced by the composition of culture media.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Molecular and Cell Biology, Singapore. yawen@imcb.a-star.edu.sg

ABSTRACT

Background: Xanthomonas oryzae pv. oryzae (Xoo) is the causal agent of rice bacterial blight disease. Xoo produces a range of virulence factors, including EPS, extracellular enzyme, iron-chelating siderophores, and type III-secretion dependent effectors, which are collectively essential for virulence. Genetic and genomics evidence suggest that Xoo might use the diffusible signal factor (DSF) type quorum sensing (QS) system to regulate the virulence factor production. However, little is known about the chemical structure of the DSF-like signal(s) produced by Xoo and the factors influencing the signal production.

Results: Xoo genome harbours an rpf cluster comprising rpfB, rpfF, rpfC and rpfG. The proteins encoded by these genes are highly homologous to their counterparts in X. campestris pv. campestris (Xcc), suggesting that Xcc and Xoo might use similar mechanisms for DSF biosynthesis and autoregulation. Consistent with in silico analysis, the rpfF mutant was DSF-deficient and the rpfC mutant produced about 25 times higher DSF-like activity than the wild type Xoo strain KACC10331. From the supernatants of rpfC mutant, we purified three compounds showing strong DSF-like activity. Mass spectrometry and NMR analysis revealed that two of them were the previously characterized DSF and BDSF; the third one was a novel unsaturated fatty acid with 2 double bonds and was designated as CDSF in this study. Further analysis showed that all the three DSF-family signals were synthesized via the enzyme RpfF encoded by Xoo2868. DSF and BDSF at a final concentration of 3 microM to the rpfF mutant could fully restore its extracellular xylanase activity and EPS production to the wild type level, but CDSF was less active than DSF and BDSF in induction of EPS and xylanase. DSF and CDSF shared a similar cell density-dependent production time course with the maximum production being detected at 42 h after inoculation, whereas the maximum production of BDSF was observed at 36 h after inoculation. When grown in a rich medium such as YEB, LB, PSA, and NYG, Xoo produced all the three signals with the majority being DSF. Whereas in nutritionally poor XOLN medium Xoo only produced BDSF and DSF but the majority was BDSF.

Conclusions: This study demonstrates that Xoo and Xcc share the conserved mechanisms for DSF biosynthesis and autoregulation. Xoo produces DSF, BDSF and CDSF signals in rich media and CDSF is a novel signal in DSF-family with two double bonds. All the three DSF-family signals promote EPS production and xylanase activity in Xoo, but CDSF is less active than its analogues DSF and BDSF. The composition and ratio of the three DSF-family signals produced by Xoo are influenced by the composition of culture media.

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Xoo produces multiple DSF-family signals. (A) HPLC analysis of the active fractions after flash column chromatography. (B) The compounds in fractions a, b, and c showed strong DSF-like activity. (C) Chemical structures of the compounds in fractions a, b, and c as confirmed by ESI-MS and NMR analysis.
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Figure 2: Xoo produces multiple DSF-family signals. (A) HPLC analysis of the active fractions after flash column chromatography. (B) The compounds in fractions a, b, and c showed strong DSF-like activity. (C) Chemical structures of the compounds in fractions a, b, and c as confirmed by ESI-MS and NMR analysis.

Mentions: To identify the DSF-like signals produced by Xoo, we prepared the DSF extracts from the culture supernatants of the rpfC mutant using a similar method as previously described [5] with two minor modifications. Firstly, we adjusted the pH of the supernatants of Xoo cell culture to 4.0 using concentrated hydrochloric acid before extraction by ethyl acetate. Secondly, formic acid was added at a final concentration of 0.1% to all the solvents for purification and high-performance liquid chromatography (HPLC) analysis. By using the DSF bioassay system described by Wang et al. [5], active fractions were collected and combined following flash column chromatography. Further separation using HPLC identified three active fractions with retention time at 15.7, 17.0, and 21.4 min, respectively, showing a maximum UV absorption at 212 nm and strong DSF activity in bioassay (Fig. 2A-B). High-resolution electrospray ionization mass spectrometry (ESI-MS) and NMR analysis showed that the compound in fraction A was cis-11-methyl-2-dodecenoic acid (DSF) (Additional file 1), which was originally reported in Xcc by Wang et al. [5]. The compound in fraction B showed the same NMR spectra and molecular weight as the BDSF signal from Burkholderia cenocepacia [9] (Additional file 2). The spectrometry data of fraction C suggested a new member of the DSF-family signals (designated as CDSF) and its characterization was discussed in the following section.


Rice bacterial blight pathogen Xanthomonas oryzae pv. oryzae produces multiple DSF-family signals in regulation of virulence factor production.

He YW, Wu J, Cha JS, Zhang LH - BMC Microbiol. (2010)

Xoo produces multiple DSF-family signals. (A) HPLC analysis of the active fractions after flash column chromatography. (B) The compounds in fractions a, b, and c showed strong DSF-like activity. (C) Chemical structures of the compounds in fractions a, b, and c as confirmed by ESI-MS and NMR analysis.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2909994&req=5

Figure 2: Xoo produces multiple DSF-family signals. (A) HPLC analysis of the active fractions after flash column chromatography. (B) The compounds in fractions a, b, and c showed strong DSF-like activity. (C) Chemical structures of the compounds in fractions a, b, and c as confirmed by ESI-MS and NMR analysis.
Mentions: To identify the DSF-like signals produced by Xoo, we prepared the DSF extracts from the culture supernatants of the rpfC mutant using a similar method as previously described [5] with two minor modifications. Firstly, we adjusted the pH of the supernatants of Xoo cell culture to 4.0 using concentrated hydrochloric acid before extraction by ethyl acetate. Secondly, formic acid was added at a final concentration of 0.1% to all the solvents for purification and high-performance liquid chromatography (HPLC) analysis. By using the DSF bioassay system described by Wang et al. [5], active fractions were collected and combined following flash column chromatography. Further separation using HPLC identified three active fractions with retention time at 15.7, 17.0, and 21.4 min, respectively, showing a maximum UV absorption at 212 nm and strong DSF activity in bioassay (Fig. 2A-B). High-resolution electrospray ionization mass spectrometry (ESI-MS) and NMR analysis showed that the compound in fraction A was cis-11-methyl-2-dodecenoic acid (DSF) (Additional file 1), which was originally reported in Xcc by Wang et al. [5]. The compound in fraction B showed the same NMR spectra and molecular weight as the BDSF signal from Burkholderia cenocepacia [9] (Additional file 2). The spectrometry data of fraction C suggested a new member of the DSF-family signals (designated as CDSF) and its characterization was discussed in the following section.

Bottom Line: Xoo produces a range of virulence factors, including EPS, extracellular enzyme, iron-chelating siderophores, and type III-secretion dependent effectors, which are collectively essential for virulence.All the three DSF-family signals promote EPS production and xylanase activity in Xoo, but CDSF is less active than its analogues DSF and BDSF.The composition and ratio of the three DSF-family signals produced by Xoo are influenced by the composition of culture media.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Molecular and Cell Biology, Singapore. yawen@imcb.a-star.edu.sg

ABSTRACT

Background: Xanthomonas oryzae pv. oryzae (Xoo) is the causal agent of rice bacterial blight disease. Xoo produces a range of virulence factors, including EPS, extracellular enzyme, iron-chelating siderophores, and type III-secretion dependent effectors, which are collectively essential for virulence. Genetic and genomics evidence suggest that Xoo might use the diffusible signal factor (DSF) type quorum sensing (QS) system to regulate the virulence factor production. However, little is known about the chemical structure of the DSF-like signal(s) produced by Xoo and the factors influencing the signal production.

Results: Xoo genome harbours an rpf cluster comprising rpfB, rpfF, rpfC and rpfG. The proteins encoded by these genes are highly homologous to their counterparts in X. campestris pv. campestris (Xcc), suggesting that Xcc and Xoo might use similar mechanisms for DSF biosynthesis and autoregulation. Consistent with in silico analysis, the rpfF mutant was DSF-deficient and the rpfC mutant produced about 25 times higher DSF-like activity than the wild type Xoo strain KACC10331. From the supernatants of rpfC mutant, we purified three compounds showing strong DSF-like activity. Mass spectrometry and NMR analysis revealed that two of them were the previously characterized DSF and BDSF; the third one was a novel unsaturated fatty acid with 2 double bonds and was designated as CDSF in this study. Further analysis showed that all the three DSF-family signals were synthesized via the enzyme RpfF encoded by Xoo2868. DSF and BDSF at a final concentration of 3 microM to the rpfF mutant could fully restore its extracellular xylanase activity and EPS production to the wild type level, but CDSF was less active than DSF and BDSF in induction of EPS and xylanase. DSF and CDSF shared a similar cell density-dependent production time course with the maximum production being detected at 42 h after inoculation, whereas the maximum production of BDSF was observed at 36 h after inoculation. When grown in a rich medium such as YEB, LB, PSA, and NYG, Xoo produced all the three signals with the majority being DSF. Whereas in nutritionally poor XOLN medium Xoo only produced BDSF and DSF but the majority was BDSF.

Conclusions: This study demonstrates that Xoo and Xcc share the conserved mechanisms for DSF biosynthesis and autoregulation. Xoo produces DSF, BDSF and CDSF signals in rich media and CDSF is a novel signal in DSF-family with two double bonds. All the three DSF-family signals promote EPS production and xylanase activity in Xoo, but CDSF is less active than its analogues DSF and BDSF. The composition and ratio of the three DSF-family signals produced by Xoo are influenced by the composition of culture media.

Show MeSH
Related in: MedlinePlus