Manganese(II) complexes of substituted salicylaldehydes and α-diimines: Synthesis, characterization and biological activity.

The interaction of Mn+2 with substituted salicylaldehydes (X-saloH) led to the formation of five manganese(II) complexes formulated as [Μn(X-salo)2(MeOH)2]. When the reactions took place in the presence of an α-diimine such as 2,2'-bipyridine, 1,10-phenanthroline or 2,2'-bipyridylamine, five manganese(II) complexes of the formula [Mn(X-salo)2(α-diimine)] were isolated. The characterization of the complexes was accomplished by various spectroscopic techniques and single-crystal X-ray crystallography. The antioxidant activity of the compounds was evaluated via the scavenging of 1,1-diphenyl-picrylhydrazyl, 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) and hydroxyl free radicals. The antibacterial activity of the complexes was tested in vitro against Staphylococcus aureus and Xanthomonas campestris bacterial strains and was found moderate. Diverse techniques were employed to examine the interaction of the complexes with calf-thymus DNA which showed intercalation as the most possible interaction mode. The affinity of the complexes for bovine serum albumin was investigated by fluorescence emission spectroscopy and the binding constants were determined.

The Role of RelA and SpoT on ppGpp Production, Stress Response, Growth Regulation, and Pathogenicity in Xanthomonas campestris pv. campestris.

The alarmone ppGpp plays an important role in the survival of bacteria by triggering the stringent response when exposed to environmental stress. Although Xanthomonas campestris pv. campestris (Xcc), which causes black rot disease in crucifers, is a representative species of Gram-negative phytopathogenic bacteria, relatively little is known regarding the factors influencing the stringent response in this species. However, previous studies in other Gram-negative bacteria have indicated that RelA and SpoT play a critical role in ppGpp synthesis. The current study found that these proteins also had an important role in Xcc, with a ΔrelAΔspoT double mutant being unable to produce ppGpp, resulting in changes to phenotype including reduced production of exopolysaccharides (EPS), exoenzymes, and biofilm, as well the loss of swarming motility and pathogenicity. The ppGpp-deficient mutant also exhibited greater sensitivity to environment stress, being almost incapable of growth on modified minimal medium (mMM) and having a much greater propensity to enter the viable but nonculturable (VBNC) state in response to oligotrophic conditions (0.85% NaCl). These findings much advance our understanding of the role of ppGpp in the biology of Xcc and could have important implications for more effective management of this important pathogen. IMPORTANCE Xanthomonas campestris pv. campestris (Xcc) is a typical seedborne phytopathogenic bacterium that causes large economic losses worldwide, and this is the first original research article to investigate the role of ppGpp in this important species. Here, we revealed the function of RelA and SpoT in ppGpp production, physiology, pathogenicity, and stress resistance in Xcc. Most intriguingly, we found that ppGpp levels and downstream ppGpp-dependent phenotypes were mediated predominantly by SpoT, with RelA having only a supplementary role. Taken together, the results of the current study provide new insight into the role of ppGpp in the biology of Xcc, which could also have important implications for the role of ppGpp in the survival and pathogenicity of other pathogenic bacteria.

Kinetically modelled approach of xanthan production using different carbon sources: A study on molecular weight and rheological properties of xanthan.

The present study emphasizes improving the overall yield, productivity and quality of xanthan by Xanthomonas campestris using different carbon sources via optimizing the fermentation media and kinetic modelling work. After optimization, six carbon sources and one nitrogen source were selected for xanthan production in 5 L bioreactor. Kinetic modelling was applied to assess the experimental fermentation data and to check its influence on scale-up production. In this work, xanthan production reached 40.65 g/L with a growth-associated rate constant (α) of 2.831, and highest specific growth rate (µm) of 0.37/h while using maltose as the sole carbon source. Furthermore, rheological properties were determined, and Herschel-Bulkley model was employed to assess the experimental data. Interestingly, xanthan obtained from sucrose and glucose showed the highest yield stress (τ0) of 12.50 ± 0.31 and 7.17 ± 0.21. Moreover, the highest xanthan molecular weight of 3.53 × 107 and 3.25 × 107 g/mol were also found with sucrose and glucose. At last, the proposed mechanism of sugar metabolism and xanthan biosynthesis pathway were described. Conclusively, maltose appeared as the best carbon source for maximum xanthan production: while sucrose and glucose gave qualitatively best results. In short, this systematically modelled approach maximizes the potential output and provides a solid base for continuous cultivation of xanthan at large-scale production.

Cyclic-di-GMP binds to histidine kinase RavS to control RavS-RavR phosphotransfer and regulates the bacterial lifestyle transition between virulence and swimming.

The two-component signalling system (TCS) comprising a histidine kinase (HK) and a response regulator (RR) is the predominant bacterial sense-and-response machinery. Because bacterial cells usually encode a number of TCSs to adapt to various ecological niches, the specificity of a TCS is in the centre of regulation. Specificity of TCS is defined by the capability and velocity of phosphoryl transfer between a cognate HK and a RR. Here, we provide genetic, enzymology and structural data demonstrating that the second messenger cyclic-di-GMP physically and specifically binds to RavS, a HK of the phytopathogenic, gram-negative bacterium Xanthomonas campestris pv. campestris. The [c-di-GMP]-RavS interaction substantially promotes specificity between RavS and RavR, a GGDEF-EAL domain-containing RR, by reinforcing the kinetic preference of RavS to phosphorylate RavR. [c-di-GMP]-RavS binding effectively decreases the phosphorylation level of RavS and negatively regulates bacterial swimming. Intriguingly, the EAL domain of RavR counteracts the above regulation by degrading c-di-GMP and then increasing the level of phosphorylated RavS. Therefore, RavR acts as a bifunctional phosphate sink that finely controls the level of phosphorylated RavS. These biochemical processes interactively modulate the phosphoryl flux between RavS-RavR and bacterial lifestyle transition. Our results revealed that c-di-GMP acts as an allosteric effector to dynamically modulate specificity between HK and RR.

Combined dissolved oxygen tension and online viscosity measurements in shake flask cultivations via infrared fluorescent oxygen-sensitive nanoparticles.

Oxygen supply is one of the most critical process parameters in aerobic cultivations. To assure sufficient oxygen supply, shake flasks are usually used in combination with orbital shaking machines. In this study, a measurement technique for the dissolved oxygen tension (DOT) in shake flask cultures with viscosity changes is presented. The movement of the shaker table is monitored by means of a Hall effect sensor. For DOT measurements, infrared fluorescent oxygen-sensitive nanoparticles are added to the culture broth. The position of the rotating bulk liquid needs to be determined to assure measurements inside the liquid. The leading edge of the bulk liquid is detected based on the fluorescence signal intensity of the oxygen-sensitive nanoparticles. Furthermore, online information about the viscosity of the culture broth is acquired due to the detection of the position of the leading edge of the bulk liquid relative to the direction of the centrifugal force, as described by Sieben et al. (2019. Sci. Rep., 9, 8335). The DOT measurement is combined with a respiration activity monitoring system which allows for the determination of the oxygen transfer rate (OTR) in eight parallel shake flasks. Based on DOT and OTR, the volumetric oxygen transfer coefficient (kL a) is calculated during cultivation. The new system was successfully applied in cultivations of Escherichia coli, Bacillus licheniformis, and Xanthomonas campestris.

Antibacterial Radicicol Analogues from Pochonia chlamydosporia and Their Biosynthetic Gene Cluster.

Chemical investigation of fungus Pochonia chlamydosporia strain 170, derived from rice fermentation sediment samples, afforded seven radicicol analogues, including two new compounds, monocillin VI (1) and monocillin VII (2), and five known compounds, monocillin II (3), monorden D (4), monocillin IV (5), monocillin V (6), and pochonin M (7). The structures of compounds 1-7 were established primarily by analysis of nuclear magnetic resonance data, and the absolute configurations of the secondary alcohol in compounds 1 and 2 were assigned by the modified Mosher method. All seven compounds have modest antibacterial activities, with a minimal inhibitory concentration (MIC) of 25.6 µg/mL for compounds 1 and 3-7 and 51.2 µg/mL for compound 2, on inhibition of the growth of the plant pathogen Xanthomonas campestris (the positive control ampicillin showed a MIC value of 12.8 µg/mL), indicating that the fungus has the potential to control bacterial disease. The biosynthetic gene cluster and putative biosynthetic pathways of these radicicol analogues in the P. chlamydosporia genome were proposed. These findings increase our knowledge of the chemical potential of P. chlamydosporia and may allow us to better utilize the fungus as a biological control agent.

Selection of Optimized Reference Genes for qRT-PCR Normalization in Xanthomonas campestris pv. campestris Cultured in Different Media.

Black rot is a cruciferous disease caused by Xanthomonas campestris pv. campestris (Xcc) and results in significant economic losses worldwide; therefore, elucidation of the mechanism of Xcc pathogenesis is urgently required. In this study, we aimed to select optimized reference genes to verify the relative quantification of virulent genes in Xcc. Xcc strains were cultured in three different media [basic medium (MMX), hrp-inducing medium (MMXC) and rich medium (NYG)] and the expression stability of five candidate genes [thymidylate synthase (thyA), DNA gyrase subunit B (gyrB), DNA-directed RNA polymerase subunit beta, glyceraldehyde-3-phosphate dehydrogenase and 16S ribosomal RNA (16S rRNA)] was evaluated using BestKeeper, GeNorm, and NormFinder software programs. Quantitative real-time PCR (qRT-PCR) analysis confirmed that two Xcc effector genes were hrpX/hrpG-regulated in MMXC using selected genes as controls. Finally, gyrB and thyA were validated as the optimized reference genes of Xcc cultured in MMXC, and qRT-PCR analysis was demonstrated to be an efficient alternative to Gus-activity detection for the analysis of Xcc expression. This information will be useful in the future studies of Xcc, especially those seeking new functional genes.

Design and effectiveness of pulsed electric fields towards seed disinfection.

BACKGROUND: Seeds harbor different microorganisms on their surfaces that degrade seed quality, thus causing an economic loss. Even though different approaches are available for the disinfection of seed surfaces, there is a need to develop environmentally friendly and sustainable technologies. A bench-scale pulsed electric field (PEF) unit was designed to inactivate microflora of eight seeds after which the resultant vigor of the treated seeds was determined. RESULTS: Significant reductions were obtained in endogenous natural and inoculated pathogenic (Alternaria brassica and Xanthomonas campestris pv. campestris, Drechslera graminea and Fusarium graminearum) microflora of seeds. The survival ratios of total aerobic mesophilic bacteria and of total mold and yeast decreased significantly for winter wheat and barley, parsley, onion, lettuce, tomato, and garden rocket with the PEF treatments of 240 and 960 J. A significant increase in germination ratio was observed for winter wheat and barley, lettuce, and tomato with 960 J. Germination energy increased for parsley with 240 J and for winter wheat and barley, lettuce, tomato, and garden rocket with 960 J. A better root development and seedling were found for winter barley. CONCLUSION: PEFs are a viable option to both disinfect seed surfaces and improve seed vigor. © 2019 Society of Chemical Industry.

Regulatory associations between the metabolism of sulfur-containing amino acids and xanthan biosynthesis in Xanthomonas campestris pv. campestris B100.

The γ-proteobacterium Xanthomonas campestris pv. campestris (Xcc) B100 synthesizes the exopolysaccharide xanthan, a commercially relevant thickening agent produced commonly by industrial scale fermentation. This work was inspired by the observation that methionine is an inhibitor of xanthan formation in growth experiments. Therefore, the global effects of methionine supplementation were characterized through cultivation experiments, genome-wide microarray hybridizations and qRT-PCR. Specific pull down of DNA-binding proteins by using the intergenic regions upstream of xanA, gumB and gumD led to the identification of six transcriptional regulators, among them the LysR-family transcriptional regulator CysB. An insertion mutant of this gene was analyzed by growth experiments, microarray experiments and qRT-PCR. Based on our experimental data, we developed a model that describes the methionine-dependent co-regulation of xanthan and sulfur-containing compounds in Xanthomonas. These data substantially contribute to better understand the impact of methionine as a compound in xanthan production media used in industrial fermentations.

A type III effector XopLXcc8004 is vital for Xanthomonas campestris pathovar campestris to regulate plant immunity.

Xanthomonas campestris pv. campestris (Xcc) secretes a suite of effectors into host plants via the type III secretion system (T3SS), modulating plant immunity defenses. Strain Xcc8004 causes black rot in brassica plants, including Arabidopsis thaliana, making it a classical model for the study of Xanthomonas pathogenesis. XopLXcc8004 was defined as a T3SS effector (T3SE) since its homologues XopLXcv85-10 from Xanthomonas campestris pv. vesicatoria (Xcv85-10) contribute to virulence in host plants. Except for its virulence on Chinese radish plants, little was previously known about the regulation and function of XopLXcc8004. Here, we tested the role of XopLXcc8004 in the pathogenicity of Xcc8004 on different host plants including Arabidopsis. We found that it was required for full virulence of Xcc8004 in Chinese cabbage. XopLXcc8004 promoted bacterial infection in Arabidopsis and suppressed bacterial flagellin (flg22)-induced FRK1 transcription, reactive oxygen species (ROS) burst, callose deposition, and pathogenesis-related marker gene expression, but it did not affect mitogen-activated protein kinases (MAPKs) cascade. Early and prolonged expression of XopLXcc8004 affected Arabidopsis growth and development. We demonstrated that XopLXcc8004 is a virulence factor and interferes with innate immunity of Arabidopsis by suppressing pathogen-associated molecular pattern-triggered immunity (PTI) signaling, independent of MAPKs.

Bioproduction of low-pigment xanthan gum by a cell-wall deficient mutant of Xanthomonas campestris.

This work aims to enhance the bioproduction of xanthan gum by screening a hyper-yield producer from the wild-type Xanthomonas campestris during a long-term continuous subculture. We reported a cell-wall deficient mutant, which performed a shift of cell morphology from rod-shaped to round-shaped. Both the yield of xanthan gum and the conversion rate of feedstock were assessed using sucrose as a carbon source with the supplement of yeast extract powder, l-glutamic acid, and other raw materials. After 96 h aerobic fermentation, the yield of xanthan gum of the mutant reached up to 32 g/L, which was 3.4 times of that of the wild-type strain. The conversion rate of feedstock in the mutant was up to 92.1%, which was 3 times of that of the wild-type (31.2%). Furthermore, pigments generated were determined and compared. As a result, the fermentation broth of the wild-type performed an OD560nm of 0.296, which was 5.8 times of that (OD560nm = 0.051) of the mutant. Microscopy analysis showed that the percentage of free-living cells in broth affected the color of the final product. Moreover, the robustness of the fermentation performance of the cell-wall deficient mutant at a pilot scale showed potential for industrial application.

Specific growth inhibitors of Ralstonia solanacearum, Xanthomonas oryzae pv. oryzae, X. campestris pv. campestris, and Clavibacter michiganensis subsp. michiganensis.

Plant pathogenic bacteria cause huge yield losses in crops globally. Therefore, finding effective bactericides to these pathogens is an immediate challenge. In this study, we sought compounds that specifically inhibit the growth of Ralstonia solanacearum. As a result, we identified one promising compound, 1-(4-bromophenyl)-6-methoxy-2,3,4,9-tetrahydro-1H-ß-carboline, which inhibited the growth of R. solanacearum (Rs1002) from a pilot library of 376 chemicals provided from RIKEN. We further obtained its structural analogues and assessed their ability to inhibit Rs1002 growth. Then we identified five compounds, named ralhibitins A to E, that specifically inhibit growth of Rs1002 at >5 µg/ml final concentration. The most effective compounds, ralhibitins A, C, and E completely inhibited the growth of Rs1002 at 1.25 µg/ml. In addition, ralhibitins A to E inhibited growth of Xanthomonas oryzae pv. oryzae but not the other bacteria tested at a final concentration of 10 µg/ml. Whereas, ralhibitin E, besides inhibiting R. solanacearum and X. oryzae pv. oryzae, completely inhibited the growth of X. campestris pv. campestris and the Gram-positive bacterium Clavibacter michiganensis subsp. michiganensis at 10 µg/ml. Growth inhibition by these compounds was stable at pH 6-9 and after autoclaving. Because Rs1002 grew in the culture medium in which ralhibitins were incubated with the ralhibitin-insensitive bacteria, the unaffected bacteria may be able to inactivate the inhibitory effect of ralhibitins. These results suggest that ralhibitins might be potential lead compounds for the specific control of phytopathogenic bacteria.

The Gram-negative phytopathogen Xanthomonas campestris pv. campestris employs a 5'UTR as a feedback controller to regulate methionine biosynthesis.

The synthesis of methionine is critical for most bacteria. It is known that cellular methionine has a feedback effect on the expression of met genes involved in de novo methionine biosynthesis. Previous studies revealed that Gram-negative bacteria control met gene expression at the transcriptional level by regulator proteins, while most Gram-positive bacteria regulate met genes at post-transcriptional level by RNA regulators (riboregulators) located in the 5'UTR of met genes. However, despite its importance, the methionine biosynthesis pathway in the Gram-negative Xanthomonas genus that includes many important plant pathogens is completely uncharacterized. Here, we address this issue using the crucifer black rot pathogen Xanthomonas campestris pv. campestris (Xcc), a model bacterium in microbe-plant interaction studies. The work identified an operon (met) involved in de novo methionine biosynthesis in Xcc. Disruption of the operon resulted in defective growth in methionine-limited media and in planta. Western blot analysis revealed that the expression of the operon is dependent on methionine levels. Further molecular analyses demonstrated that the 5'UTR, but not the promoter of the operon, is involved in feedback regulation on operon expression in response to methionine availability, providing an example of a Gram-negative bacterium utilizing a 5'UTR region to control the expression of the genes involved in methionine biosynthesis.

Comparative transcription profiling of two fermentation cultures of Xanthomonas campestris pv. campestris B100 sampled in the growth and in the stationary phase.

The ɣ-proteobacterium Xanthomonas campestris pv. campestris (Xcc) is the producer of the biopolymer xanthan, a polysaccharide which is used as a thickener in numerous industrial applications. In this study, we present a global transcriptome profiling of two Xcc strain B100 cultures obtained from fermentation during the growth phase and the subsequent stationary phase associated with xanthan biosynthesis. During the xanthan production phase, highly abundant transcripts belonged to genes encoding for small RNAs, glycogen biosynthesis, and xanthan export. A total of 1850 (40%) genes were differentially transcribed during the stationary phase where 924 were transcriptionally up-regulated and 926 genes were down-regulated. An overview of differentially transcribed genes includes a significant down-regulation of genes involved in transcription, translation, and amino acid biosynthesis pathways. A group of up-regulated genes was involved in cellular response against oxidative stress, such as those coding for superoxide dismutase and catalase. Genes encoding enzymes involved in nucleotide sugar precursor synthesis of xanthan biosynthesis, such as xanA, galU, and ugd, exhibited a transcription pattern that did not change during the growth and stationary phase. Regarding the transcription pattern of the gum gene cluster that govern xanthan biosynthesis, a significant up-regulation of the genes gumB, gumC, and gumD was observed, while the transcript pools of the genes gumG, gumH, gumI, and gumJ were reduced and those of genes gumE, gumF, gumK, gumL, and gumM remained un-changed during the stationary phase compared to the growth phase. The obtained data represents the first analysis of gene expression patterns under xanthan production conditions and provides the bases for future studies aiming at enhancing xanthan yield.

Novel Xanthomonas campestris Long-Chain-Specific 3-Oxoacyl-Acyl Carrier Protein Reductase Involved in Diffusible Signal Factor Synthesis.

The precursors of the diffusible signal factor (DSF) family signals of Xanthomonas campestris pv. campestris are 3-hydroxyacyl-acyl carrier protein (3-hydroxyacyl-ACP) thioesters having acyl chains of 12 to 13 carbon atoms produced by the fatty acid biosynthetic pathway. We report a novel 3-oxoacyl-ACP reductase encoded by the X. campestris pv. campestris XCC0416 gene (fabG2), which is unable to participate in the initial steps of fatty acyl synthesis. This was shown by the failure of FabG2 expression to allow growth at the nonpermissive temperature of an Escherichia colifabG temperature-sensitive strain. However, when transformed into the E. coli strain together with a plasmid bearing the Vibrio harveyi acyl-ACP synthetase gene (aasS), growth proceeded, but only when the medium contained octanoic acid. In vitro assays showed that FabG2 catalyzes the reduction of long-chain (≥C8) 3-oxoacyl-ACPs to 3-hydroxyacyl-ACPs but is only weakly active with shorter-chain (C4, C6) substrates. FabG1, the housekeeping 3-oxoacyl-ACP reductase encoded within the fatty acid synthesis gene cluster, could be deleted in a strain that overexpressed fabG2 but only in octanoic acid-supplemented media. Growth of the X. campestris pv. campestris ΔfabG1 strain overexpressing fabG2 required fabH for growth with octanoic acid, indicating that octanoyl coenzyme A is elongated by X. campestris pv. campestrisfabH Deletion of fabG2 reduced DSF family signal production, whereas overproduction of either FabG1 or FabG2 in the ΔfabG2 strain restored DSF family signal levels.IMPORTANCE Quorum sensing mediated by DSF signaling molecules regulates pathogenesis in several different phytopathogenic bacteria, including Xanthomonas campestris pv. campestris DSF signaling also plays a key role in infection by the human pathogen Burkholderia cepacia The acyl chains of the DSF molecules are diverted and remodeled from a key intermediate of the fatty acid synthesis pathway. We report a Xanthomonas campestris pv. campestris fatty acid synthesis enzyme, FabG2, of novel specificity that seems tailored to provide DSF signaling molecule precursors.

Loss of chloroplast-localized protein phosphatase 2Cs in Arabidopsis thaliana leads to enhancement of plant immunity and resistance to Xanthomonas campestris pv. campestris infection.

Protein phosphatases (PPs) counteract kinases in reversible phosphorylation events during numerous signal transduction pathways in eukaryotes. PP2Cs, one of the four major classes of the serine/threonine-specific PP family, are greatly expanded in plants. Thus, PP2Cs are thought to play a specific role in signal transduction pathways. Some rice PP2Cs classified in subgroup K are responsive to infection by the compatible Xanthomonas oryzae pv. oryzae, the causal agent of bacterial blight. In Arabidopsis thaliana, orthologous PP2C genes (AtPP2C62 and AtPP2C26) classified to subgroup K are also responsive to Xanthomonas campestris pv. campestris (Xcc, causal agent of black rot) infection. To elucidate the function of these subgroup K PP2Cs, atpp2c62- and atpp2c26-deficient A. thaliana mutants were characterized. A double mutant plant which was inoculated with a compatible Xcc showed reduced lesion development, as well as the suppression of bacterial multiplication. AtPP2C62 and AtPP2C26 localized to the chloroplast. Furthermore, the photosynthesis-related protein, chaperonin-60, was indicated as the potential candidate for the dephosphorylated substrate catalysed by AtPP2C62 and AtPP2C26 using two-dimensional isoelectric focusing sodium dodecylsulfate-polyacrylamide gel electrophoresis (2D-IDF-SDS-PAGE). Taken together, AtPP2C62 and AtPP2C26 are suggested to be involved in both photosynthesis and suppression of the plant immune system. These results imply the occurrence of crosstalk between photosynthesis and the plant defence system to control productivity under pathogen infection.

Probing the Role of Cyclic di-GMP Signaling Systems in Disease Using Chinese Radish.

The determination of the genome sequences of pathogenic bacteria has facilitated functional analyses that aim to understand the molecular basis of virulence. In particular, genome sequence information of the pathogen Xanthomonas campestris pathovar campestris has allowed researchers to identify and functionally analyze the role of intracellular signaling involving cyclic di-GMP in black rot disease of crucifers. Here, we describe leaf clipping and spraying methods for testing the virulence of wild type and derived mutants of X. campestris in Chinese radish. These methods address different facets of the disease cycle, which requires the ability to survive epiphytically before entry into the plant and growth and systemic spread within the xylem.

XC_0531 encodes a c-type cytochrome biogenesis protein and is required for pathogenesis in Xanthomonas campestris pv. campestris.

BACKGROUND: The phytopathogenic Xanthomonas campestris pv.campestris is a gram-negative bacterium and the causal agent of black-rot disease of cruciferous crops. Many gram-negative bacteria possess a family of proteins, called Dsbs, which are involved in disulfide bond formation in certain periplasmic proteins. In our preliminary screening of the virulence to the plants we identified that gene XC_0531 which annotated gene dsbD of Xanthomonas campestris pv. campestris (Xcc) is related to the virulence to the host plants. RESULTS: Here, we found XC_0531 encoded a DsbD like protein. Its deletion is sensitive to DTT and copper, decreased accumulation of free thiols in periplasm. Its deletion also affected heme synthesis, position of Soret band and the production of peak c550. This suggests that XC_0531 is related to c-type cytochromes biogenesis. XC_0531 mutation decreased the utilization of different carbon sources (such as galactose, xylose, maltose, saccharose and glucose), reduced extracellular polysaccharide (EPS) production, decreased extracellular enzyme activities (protease, cellulose and amylase), slowed down growth rate of Xcc and weakened virulence to the plants. These results suggest that these phenotypes caused by XC_0531 mutation is possibly due to deficient biosynthesis of c-type cytochromes in respiration chain and the formation of disulfide bonds. Our work confirmed the function of XC_0531 and provide theory basis for scientists working on molecular mechanisms of cytochrome c biogenesis, pathogenesis of Xcc, development of EPS commercial values and protecting plant from black rot. CONCLUSION: We confirmed the function of gene XC_0531, which encodes a DsbD like protein, a protein correlated with c-type cytochrome biogenesis. This gene is related to the virulence to plants by affecting funtion of cytochromes c and probably disulfide bonds modification of proteins in type II secretion system (T2SS).

High production of xanthan gum by a glycerol-tolerant strain Xanthomonas campestris WXLB-006.

The superior properties of xanthan gum make it an industrial aginomoto used in many industries, especially in oil recovery. In the present work, xanthan production from glycerol by a mutant strain Xanthomonas campestris WXLB-006 reached as high as 17.8 g/L in flask culture. With the adoption of pH control, varied aeration and agitation, and varied glycerol feeding strategy, xanthan production reached 33.9 g/L in a 7-L fermenter and fermentation time decreased to 60 hr. Instead of difficultly and costly purifying glycerol, this research provides a very good case for glycerol utilization. At the same time, this is the first report on a high glycerol-tolerant strain for microbial polysaccharide production and 33.9 g/L is the highest production of xanthan gum produced from glycerol so far.