Redox proteomic study of Bacillus cereus thiol proteome during fermentative anaerobic growth

Background Bacillus cereus is a notorious foodborne pathogen, which can grow under anoxic conditions. Anoxic growth is supported by endogenous redox metabolism, for which the thiol redox proteome serves as an interface. Here, we studied the cysteine (Cys) proteome dynamics of B. cereus ATCC 14579 cells grown under fermentative anoxic conditions. We used a quantitative thiol trapping method combined with proteomics profiling. Results In total, we identified 153 reactive Cys residues in 117 proteins participating in various cellular processes and metabolic pathways, including translation, carbohydrate metabolism, and stress response. Of these reactive Cys, 72 were detected as reduced Cys. The B. cereus Cys proteome evolved during growth both in terms of the number of reduced Cys and the Cys-containing proteins identified, reflecting its growth-phase-dependence. Interestingly, the reduced status of the B. cereus thiol proteome increased during growth, concomitantly to the decrease of extracellular oxidoreduction potential. Conclusions Taken together, our data show that the B. cereus Cys proteome during unstressed fermentative anaerobic growth is a dynamic entity and provide an important foundation for future redox proteomic studies in B. cereus and other organisms.

Domestication of the novel alcohologenic acetogen Clostridium sp. AWRP: from isolation to characterization for syngas fermentation

Background Gas-fermenting acetogens have received a great deal of attention for their ability to grow on various syngas and waste gas containing carbon monoxide (CO), producing acetate as the primary metabolite. Among them, some Clostridium species, such as C. ljungdahlii and C. autoethanogenum, are of particular interest as they produce fuel alcohols as well. Despite recent efforts, alcohol production by these species is still unsatisfactory due to their low productivity and acetate accumulation, necessitating the isolation of strains with better phenotypes. Results In this study, a novel alcohol-producing acetogen (Clostridium sp. AWRP) was isolated, and its complete genome was sequenced. This bacterium belongs the same phylogenetic group as C. ljungdahlii, C. autoethanogenum, C. ragsdalei, and C. coskatii based on 16S rRNA homology; however, the levels of genome-wide average nucleotide identity (gANI) for strain AWRP compared with these strains range between 95 and 96%, suggesting that this strain can be classified as a novel species. In addition, strain AWRP produced a substantial amount of ethanol (70–90 mM) from syngas in batch serum bottle cultures, which was comparable to or even exceeded the typical values obtained using its close relatives cultivated under similar conditions. In a batch bioreactor, strain AWRP produced 119 and 12 mM of ethanol and 2,3-butanediol, respectively, while yielding only 1.4 mM of residual acetate. Interestingly, the alcohologenesis of this strain was strongly affected by oxidoreduction potential (ORP), which has not been reported with other gas-fermenting clostridia. Conclusion Considering its ethanol production under low oxidoreduction potential (ORP) conditions, Clostridium sp. AWRP will be an interesting host for biochemical studies to understand the physiology of alcohol-producing acetogens, which will contribute to metabolic engineering of those strains for the production of alcohols and other value-added compounds from syngas.

Presumptive Relationship between Oxidoreduction Potential and Both Antibacterial and Antioxidant Activities of Herbs and Spices: Oxidoreduction Potential as a Companion Tool for Measuring the Antioxidant Activity

Antibacterial and antioxidant activities form an essential component of the bioactive properties of plant products. The antibacterial and the antioxidant properties of three types of aqueous extracts of four herbs and spices were evaluated. While the total phenolic content, DPPH radical scavenging activity and oxidoreduction potential methods were used for the antioxidant properties determination, the inhibition diameters of extracts toward the growth of Staphylococcus warneri, Bacillus cereus, Enterobacter cloacae and Proteus vulgaris were evaluated. Although the phenolic content did not correlate with the antibacterial activity of plant extracts, it linearly correlated (R2 = 0.827) with DPPH scavenging activity of the studied plants following the order: sumac > ginger > rosemary > cinnamon. The oxidoreduction potential values linearly correlated with both the phenolic content (R2 ≈ 0.88) and DPPH scavenging activity values (R2 ≈ 0.96). The oxidoreduction potential could be proposed as a useful companion tool combined with other techniques when determining the antioxidant activity of plant extracts and food products is considered.