maltophilia by electrospray ionization mass spectrometry (ESI-MS) and gas chromatography and mass spectrometry (GC-MS analysis) . Functional analysis of rpfF or rpfC mutants in different bacterial species suggests that the general Selleckchem BVD-523 role of the DSF-signaling system in the modulation of virulence seems to be conserved, but the regulatory mechanisms and DSF-dependent traits may differ among taxa [8, 15–17]. Xanthomonas oryzae pv. oryzae (Xoo) is a causal
agent of bacterial blight disease of rice . Xoo enters either through wounds or hydathodes, XAV-939 clinical trial multiplies in the epitheme and moves to the xylem vessels where active multiplication results in blight disease symptoms on rice leaves. Similar to Xcc, Xoo also produces a range of virulence factors, including EPS, extracellular enzyme, iron-chelating siderophores, and the Sepantronium nmr type III-secretion dependent effectors, which are collectively essential for virulence [19–23]. Null mutation of rpfC in Xoo wild type strain T3000 substantially affects the EPS synthesis and virulence . The rpfF mutants of an Indian Xoo wild type isolate BXO43 are attenuated in virulence and defective in
growth under low iron conditions . More recently, a report showed that mutations in the core rpf genes rpfB, rpfF, rpfC and rpfG reduced the EPS levels, xylanase activity, motility, and virulence of Xoo strain KACC10331 . These findings suggest that DSF signalling
system in Xoo much is involved in the regulation of virulence factor production. However, little is known about the chemical structure of the DSF-family signals in Xoo and the factors influencing the signal production. In this study, the comparative genomics analysis revealed that Xoo genome shares the key components of DSF biosynthesis and signalling with Xcc. The DSF production assay of rpfF, rpfC, rpfG mutants showed that Xoo uses a similar autoregulation mechanism as Xcc to control DSF biosynthesis. We further found that Xoo produces three DSF-family signals: DSF, BDSF and a novel signal with two double bonds, which was designated as CDSF. All the three DSF-family signals induce the EPS production and extracellular xylanase activity in the rpfF mutant of Xoo with variable efficiencies. Moreover, we found that the production and the ratio of the DSF-family signals are affected by the culture medium composition. Results Xoo uses the similar mechanism of Xcc in autoregulation of DSF biosynthesis In Xcc, the rpf cluster is involved in DSF biosynthesis, signal sensing and response. RpfF, a putative enoyl-CoA hydratase, is a key enzyme involved in DSF biosynthesis and mutation of rpfF abolishes DSF production . RpfC negatively controls DSF biosynthesis by binding to RpfF at low cell density , and disruption of rpfC results in a 16-fold higher DSF accumulation than the wild-type Xcc [5, 11].