A dissimilatory nitrate reduction to ammonium (DNRA) microbial community was developed under a high organic carbon to nitrate (C/NO3–) ratio in an anoxic semi-continuous sequencing batch reactor (SBR) fed with glucose as the source of carbon and NO3– as the electron acceptor. Activated sludge collected from a municipal wastewater treatment plant with good denitrification efficiency was used as the inoculum to start the system. The aim of this study was to examine the microbial populations in a high C/NO3– ecosystem for potential DNRA microorganisms, which are the microbial group with the ability to reduce NO3– to ammonium (NH4+). A low C/NO3– reactor was operated in parallel for direct comparisons of the microbial communities that developed under different C/NO3– values. The occurrence of DNRA in the high C/NO3– SBR was evidenced by stable isotope-labeled nitrate and nitrite (15NO3– and 15NO2–), which proved the formation of NH4+ from dissimilatory NO3–/NO2– reduction, in which both nitrogen oxides induced DNRA activity in a similar manner. An analysis of sludge samples with Illumina MiSeq 16S rRNA sequencing showed that the predominant microorganisms in the high C/NO3– SBR were related to Sulfurospirillum and the family Lachnospiraceae, which were barely present in the low C/NO3– system. A comparison of the populations and activities of the two reactors indicated that these major taxa play important roles as DNRA microorganisms under the high C/NO3– condition. Additionally, a beta-diversity analysis revealed distinct microbial compositions between the low and high C/NO3– SBRs, which reflected the activities observed in the two systems.
In the model species Streptomyces coelicolor A3(2), the uptake of chitin-degradation byproducts, mainly N,N′-diacetylchitobiose ([GlcNAc]2) and N-acetylglucosamine (GlcNAc), is performed by the ATP-binding cassette (ABC) transporter DasABC-MsiK and the sugar-phosphotransferase system (PTS), respectively. Studies on the S. coelicolor chromosome have suggested the occurrence of additional uptake systems of GlcNAc-related compounds, including the SCO6005-7 cluster, which is orthologous to the ABC transporter NgcEFG of S. olivaceoviridis. However, despite conserved synteny between the clusters in S. coelicolor and S. olivaceoviridis, homology between them is low, with only 35% of residues being identical between NgcE proteins, suggesting different binding specificities. Isothermal titration calorimetry experiments revealed that recombinant NgcESco interacts with GlcNAc and (GlcNAc)2, with Kd values (1.15 and 1.53 μM, respectively) that were higher than those of NgcE of S. olivaceoviridis (8.3 and 29 nM, respectively). The disruption of ngcESco delayed (GlcNAc)2 consumption, but did not affect GlcNAc consumption ability. The ngcESco-dasA double mutation severely decreased the ability to consume (GlcNAc)2 and abolished the induction of chitinase production in the presence of (GlcNAc)2, but did not affect the GlcNAc consumption rate. The results of these biochemical and reverse genetic analyses indicate that NgcESco acts as a (GlcNAc)2-binding protein of the ABC transporter NgcEFGSco-MsiK. Transcriptional and biochemical analyses of gene regulation demonstrated that the ngcESco gene was slightly induced by GlcNAc, (GlcNAc)2, and chitin, but repressed by DasR. Therefore, a model was proposed for the induction of the chitinolytic system and import of (GlcNAc)2, in which (GlcNAc)2 generated from chitin by chitinase produced leakily, is mainly transported via NgcEFG-MsiK and induces the expression of chitinase genes and dasABCD.
Diarrhea is often associated with marked alterations in the intestinal microbiota, termed dysbiosis; however, limited information is currently available on the intestinal microbiota in captive golden snub-nosed monkeys (Rhinopithecus roxellana) with diarrhea. We herein characterized the fecal microbiota in diarrhea and healthy monkeys using the Illumina MiSeq platform. The concentrations of fecal short-chain fatty acids (SCFAs) and copy numbers of virulence factor genes were also assessed using gas chromatography and quantitative PCR (qPCR), respectively. The results obtained showed that diarrhea monkeys harbored a distinctive microbiota from that of healthy monkeys and had 45% fewer Bacteroidetes. Among healthy subjects, old monkeys had the lowest relative abundance of Bacteroidetes. Linear discriminant analysis coupled with the effect size (LEfSe) and canonical correlation analysis (CCA) identified significant differences in microbial taxa between diarrhea and healthy monkeys. A PICRUSt analysis revealed that several pathogenic genes were enriched in diarrhea monkeys, while glycan metabolism genes were overrepresented in healthy monkeys. A positive correlation was observed between the abundance of nutrition metabolism-related genes and the individual digestive capacities of healthy monkeys. Consequently, the abundance of genes encoding heat stable enterotoxin was significantly higher in diarrhea monkeys than in healthy monkeys (P<0.05). In healthy subjects, adult monkeys had significant higher concentrations of butyrate and total SCFAs than old monkeys (P<0.05). In conclusion, the present study demonstrated that diarrhea had a microbial component and changes in the microbial structure were accompanied by altered systemic metabolic states. These results suggest that pathogens and malabsorption are the two main causes of diarrhea, which are closely related to the microbial structure and functions.