A single amino acid substitution in the SdhB protein of succinate dehydrogenase determines resistance to amicarthiazol in Xanthomonas oryzae pv. oryzae

Mining the Flavoproteome of Brucella ovis, the Brucellosis Causing Agent in Ovis aries

Flavoproteins are a diverse class of proteins that are mostly enzymes and contain as cofactors flavin mononucleotide (FMN) and/or flavin adenine dinucleotide (FAD), which enable them to participate in a wide range of physiological reactions. We have compiled 78 potential proteins building the flavoproteome of Brucella ovis (B. ovis), the causative agent of ovine brucellosis. The curated list of flavoproteins here reported is based on (i) the analysis of sequence, structure and function of homologous proteins, and their classification according to their structural domains, clans, and expected enzymatic functions; (ii) the constructed phylogenetic trees of enzyme functional classes using 19 Brucella strains and 26 pathogenic and/or biotechnological relevant alphaproteobacteria together with B. ovis; and (iii) the evaluation of the genetic context for each entry. Candidates account for ∼2.7% of the B. ovis proteome, and 75% of them use FAD as cofactor. Only 55% of these flavoproteins belong to the core proteome of Brucella and contribute to B. ovis processes involved in maintenance activities, survival and response to stress, virulence, and/or infectivity. Several of the predicted flavoproteins are highly divergent in Brucella genus from revised proteins and for them it is difficult to envisage a clear function. This might indicate modified catalytic activities or even divergent processes and mechanisms still not identified. We have also detected the lack of some functional flavoenzymes in B. ovis, which might contribute to it being nonzoonotic. Finally, potentiality of B. ovis flavoproteome as the source of antimicrobial targets or biocatalyst is discussed. IMPORTANCE Some microorganisms depend heavily on flavin-dependent activities, but others maintain them at a minimum. Knowledge about flavoprotein content and functions in different microorganisms will help to identify their metabolic requirements, as well as to benefit either industry or health. Currently, most flavoproteins from the sheep pathogen Brucella ovis are only automatically annotated in databases, and only two have been experimentally studied. Indeed, certain homologues with unknown function are not characterized, and they might relate to still not identified mechanisms or processes. Our research has identified 78 members that comprise its flavoproteome, 76 of them flavoenzymes, which mainly relate to bacteria survival, virulence, and/or infectivity. The list of flavoproteins here presented allows us to better understand the peculiarities of Brucella ovis and can be applied as a tool to search for candidates as new biocatalyst or antimicrobial targets.

Antibacterial pathway of cefquinome against Staphylococcus aureus based on label-free quantitative proteomics analysis

Cefquinome (CEQ) is a novel β-lactam antibiotic that exhibits excellent antibacterial activity against Staphylococcus aureus. However, the bacterial protein targets of CEQ are unclear. To evaluate the relationship between the pharmacokinetic/pharmacodynamic (PK/PD) parameters of CEQ and strains with varying degrees of resistance and to elucidate bacterial protein responses to CEQ treatment, label-free quantitative proteomics analysis was conducted. The sensitive S. aureus ATCC6538 and the resistant 2MIC and 8MIC were tested for differentially expressed proteins. An in vitro model was treated with different concentrations of CEQ (3, 5, or 10 µg/ml) with different terminal half-lives (2.5 or 5 h) at different intervals (12 or 24 h). Differentially expressed proteins were evaluated using Gene Ontology analysis followed by KEGG pathway enrichment analysis and STRING network analysis. RT-qPCR was performed to validate the differentially expressed proteins at the molecular level. The results showed that the degree of resistance increased in a cumulative manner and increased gradually with the extension of administration time. The resistant strain would not have appeared in the model only if %T > mutant prevention concentration ≥ 50%. The expression of 45 proteins significantly changed following CEQ treatment, among which 42 proteins were obviously upregulated and 3 were downregulated. GO analysis revealed that the differentially expressed proteins were mainly present on cells and the cell membrane, participated in metabolic and intracellular processes, and had catalytic and binding activities. The RPSO, SDHB, CITZ, ADK, and SAOUHSC 00113 genes in S. aureus may play important roles in the development of resistance to CEQ. These results provided important reference candidate proteins as targets for overcoming S. aureus resistance to CEQ.

Synthesis of Novel Thiazolyl Hydrazine Derivatives and Their Antifungal Activity

A series of novel thiazolyl hydrazine derivatives 3a–3o were synthesized and evaluated for their in vitro antifungal activity against six phytopathogenic strains, namely, Botryosphaeria dothidea (B. d.), Gibberella sanbinetti (G. s.), Fusarium oxysporum (F. o.), Thanatephorus cucumeris (T. c.), Sclerotinia sclerotiorum (S. s.), and Verticillium dahliae (V. d.), by the classical mycelial growth rate method. Biological assessment results showed that most of these target compounds showed good antifungal activity toward tested strains. Especially, compound 3l showed excellent antifungal activities against B. d. and G. s. with relatively lower EC50 values of 0.59 and 0.69 µg/mL, respectively, which were extremely superior to those of commercial fungicides fluopyram, boscalid, and hymexazol and were comparable to those of carbendazim. Given the excellent bioactivity of designed compounds, this kind of thiazolyl hydrazine framework can provide a suitable point for exploring highly efficient antifungal agents.

First report about the screening, characterization, and fosmid library construction of Xanthomonas oryzae pv. oryzae strain with resistance to Fubianezuofeng

Bacterial blight (BB), which is caused by Xanthomonas oryzae pv. oryzae (Xoo), is a common bacterial disease that seriously harms rice production in major rice-growing areas worldwide. Fubianezuofeng (FBEZF), a sulfone bactericide that contains an oxadiazole moiety, exerts good control effect on BB. In this study, FBEZF-resistant strains of Xoo were screened for the first time in the laboratory to evaluate the risk of Xoo developing resistance to FBEZF. Three strains with moderate resistance to FBEZF, were obtained and named as F1, F2, and F3, which have resistance factors (RF) of 14.69, 15.72, and 11.12, respectively. FBEZF lacked positive cross-resistance to bismerthiazol, thiodiazole copper, zhongshengmycin and phenazino-1-carboxylic acid. The growth rates of the resistant strains F1 and F2 were similar to those of the wild-type strain in nutrient broth medium, but differed in nutrient agar medium. The extracellular polysaccharide production and pathogenicity of F1, F2, and F3 were reduced relative to those of the wild-type strain. A fosmid library containing 2304 transformants was constructed based on the genome of F2, and transformants 2193 and 2202 exhibited FBEZF resistance. The results are helpful for further study on the molecular mechanism of resistance to FBEZF in Xoo.

Baseline sensitivity and resistance risk assessmemt of Rhizoctonia cerealis to thifluzamide, a succinate dehydrogenase inhibitor

During 2010-2012, a total of 120 isolates of Rhizoctonia cerealis were collected from wheat with symptoms of sharp eyespot in four provinces (Henan, Shandong, Anhui and Jiangsu) in China. All the isolates were determined for baseline sensitivity to thifluzamide, a succinate dehydrogenase inhibitor (SDHI) with strong antifungal activity. The sampled pathogenic populations, never exposed to SDHIs, had similar sensitivity to trifluzamide (0.025-0.359 µg/ml) in the four regions and over the two years. The baseline sensitivity was distributed as a skewed unimodal curve with a mean EC50 value (effective concentrations for 50% inhibiting mycelial growth) of 0.064 ± 0.013 µg/ml. The resistance risk of R. cerealis to thifluzamide was further evaluated in vitro. Two thifluzamide-resistant mutants of R. cerealis were obtained by culturing on thifluzamide-amended plates. The resistance factors (RF = EC50 value of a mutant/EC50 value of the wild type progenitor of the mutant) were 120 and 40 for two R. cerealis mutants, respectively. All the mutants exhibited similar fitness after 10 successive transfers when compared to their wild-type parents in mycelial growth, sclerotia production, and virulence. However, the two thifluzamide-resistant mutants differed significantly in sensitivity to boscalid and flutolanil. Therefore, a low-to-moderate risk of resistance development was recommended for thifluzamide.