Search Results (4)

Compositions and activities of bacterial flora in the gastrointestinal tract significantly influence the metabolism, health, and disease of host humans and animals. These enteric bacteria can switch between aerobic and anaerobic growth if oxygen tension becomes limited. Interestingly, the switching mechanism is important for preventing reactive oxygen species (ROS) production and antibiotic tolerance. Studies have also shown that intracellular and extracellular sulfide molecules are involved in this switching control, although the mechanism is not fully clarified. Here, we found that YgaV, a sulfide-responsive transcription factor SqrR/BigR homolog, responded to sulfide compounds in vivo and in vitro to control anaerobic respiratory gene expression. YgaV also responded to H₂O₂ scavenging in the enteric bacterium Escherichia coli. Although the wild-type (WT) showed increased antibiotic tolerance under H₂S-atmospheric conditions, the ygaV mutant did not show such a phenotype. Additionally, antibiotic sensitivity was higher in the mutant than in the WT of both types in the presence and absence of exogenous H₂S. These results, therefore, indicated that YgaV-dependent transcriptional regulation was responsible for maintaining redox homeostasis, ROS scavenging, and antibiotic tolerance. Full article

Nitrification and denitrification are important for nitrogen (N) cycling in fish ponds culture, but the effects of nitrifying and denitrifying bacteria concentrations on pond water and sediments remain largely unknown. Here, we used 0, 0.15, 0.30, 0.60 mg/L different concentrations of mixed nitrifying and denitrifying bacteria to repair the pond substrate through an enclosure experiment lasting 15 days. The results showed that the purification effect of nitrifying and denitrifying bacteria was most obvious on pond nitrogen from day 4 to day 7. The optimal relative concentration was 0.60 mg/L for nitrifying and denitrifying bacteria; NH₄⁺-N (ammonia nitrogen) decreased by 75.83%, NO₂⁻-N (nitrite) by 93.09%, NO₃⁻-N (nitrate) by 38.02%, and TN (total nitrogen) by 45.16% in this concentration group on pond water. In one cycle, C/N (carbon/nitrogen) ratio of both water body and bottom sediment significantly increased, but C/N ratio of water body increased more significantly than that of sediment. Water C/N ratio increased by 76.00%, and sediment C/N ratio increased by 51.96% in the 0.60 mg/L concentration group. Amplicon sequencing of pond sediment showed that the change in nitrifying and denitrifying bacterium diversity was consistent with that in water quality index. Dominant nitrifying bacteria had a relatively high percentage, with significant differences in dominant bacterium percentage across different bacterial addition groups, while dominant denitrifying bacterium percentage was not high without significant differences among different groups. The dominant species of nitrifying bacteria were, respectively, Nitrosomonas, Nitrosovibrio, Nitrosospira, and Aeromonas, and the dominant species of denitrifying bacteria were Thauera, Azoarcus, Magnetospirillum, Azospira, and Idiomarina. The correlation analyses showed an aerobic nitrification and facultative anaerobic denitrification in pond sediments. Research shows that the addition of exogenous nitrifying and denitrifying bacteria can effectively reduce the nitrogen load of pond water and sediment. At the concentration of 0.6 mg/L, the nitrogen load of pond water and sediment decreased most obviously, which had the best effect on pond purification. Full article

Prickly pear (Rosa roxburghii Tratt), a shrub mainly distributed in South China, is an economically essential plant for helping the local people out of poverty. To efficiently provide sufficient nutrients to the plant in the soil for the ecological cultivation of prickly pear, we studied the aerobic composting of a prickly pear litter with three agents, including AC (Bacillus natto, Bacillus sp., Actinomycetes sp., Saccharomyces sp., Trichoderma sp., Azotobacter sp., and Lactobacillus sp.), BC (Bacillus subtilis, Lactobacillaceae sp., Bacillus licheniformis, Saccharomyces sp., and Enterococcus faecalis), and CC (Bacillus sp., Actinomycetes sp., Lactobacillaceae sp., Saccharomyces sp., and Trichoderma sp.) and a control without microbial agents. The results show that the physicochemical and microbial traits of three resultant prickly pear composts were different after the inoculation with AC, BC, or CC. The pH values of three composts ranged from 8.0 to 8.5, and their conductivity values were between 1.6 and 1.9 mS/cm. The seed germination index of all three composts exceeded 70%. The contents of volatile solids and organic matter of the three composts both decreased significantly. The BC maximally increased the total N (18%) of the compost, whereas the CC maximally increased the total P (48%) and total K (38%) contents. Contents of available P and available K of the three composts increased significantly, and the available N content in compost after BC inoculation increased by 16%. The physicochemical features showed that three composts were non-hazardous to plants, and the microbial agents improved nutrient availability. The richness, Chao1, and Shannon index in the bacterial communities of three composts increased significantly. At the phylum level, Proteobacteria, Bacteroidetes, and Firmicutes bacterium became dominant in the three composts, whereas at the family level, Microscillaceae and A4b (phylum Chloroflexi) became the dominant groups. Abundant cellulose-degrading bacteria existed at the dominant phylum level, which promoted fiber degradation in composts. Organic matter and the available N content regulated the composting bacterium. The inoculants enhanced the efficiency of composting: agents B and C were more suitable exogenous inoculants for the composting of a prickly pear litter. Full article

In this work, the impact of exogenous aerobic bacteria mixture (EABM) on municipal solid waste (MSW) is well evaluated in the following aspects: biogas production, leachate analysis, organic waste degradation, EABM population, and the composition of microbial communities. The study was designed and performed as follows: the control bioreactor (R1) was filled up with MSW and the culture medium of EABM and the experimental bioreactor (R2) was filled up with MSW and EABM. The data suggests that the composition of microbial communities (bacterial and methanogenic) in R1 and R2 were similar at day 0, while the addition of EABM in R2 led to a differential abundance of Bacillus cereus, Bacillus subtilis, Staphylococcus saprophyticus, Staphlyoccus xylosus, and Pantoea agglomerans in two bioreactors. The population of exogenous aerobic bacteria in R2 greatly increased during hydrolysis and acidogenesis stages, and subsequently increased the degradation of volatile solid (VS), protein, lipid, and lignin by 59.25%, 25.68%, 60.47%, and 197.62%, respectively, compared to R1. The duration of hydrolysis and acidogenesis in R2 was 33.33% shorter than that in R1. At the end of the study, the accumulative methane yield in R2 (494.4 L) was almost three times more than that in R1 (187.4 L). In addition, the abundance of acetoclasic methanogens increased at acetogenesis and methanogenesis stages in both bioreactors, which indicates that acetoclasic methanogens (especially Methanoseata) could contribute to methane production. This study demonstrates that EABM can accelerate organic waste degradation to promote MSW biodegradation and methane production. Moreover, the operational parameters helped EABM to generate 20.85% more in accumulative methane yield. With a better understanding of how EABM affects MSW and the composition of bacterial community, this study offers a potential practical approach to MSW disposal and cleaner energy generation worldwide. Full article