High nitrite-nitrogen stress intensity drives nitrite anaerobic oxidation to nitrate and inhibits methanogenesis.

Nitrite is an important intermediate in nitrogen metabolism. We explored the effect of nitrite-nitrogen stress intensity (NNSI) on nitrite metabolism and methanogenesis in anaerobic digestion. The results showed that the NNSI regulated microbial diversity, composition, and functions, and microbial community assembly was primarily shaped by stochastic processes. Moreover, the NNSI was negatively correlated with α-diversity and positively correlated with non-metric multi-dimensional scaling distance. Denitrification gradually increased with increasing NNSI; however, methanogenesis was gradually inhibited, which was primarily due to the inhibition of the aceticlastic methanogenesis pathway (i.e., Methanosaeta) and methylotrophic methanogenesis pathway (i.e., Candidatus_Methanofastidiosum). High NNSI (1882 ± 98.99 mg/L NO2--N) promoted nitrite anaerobic oxidation to nitrate and was favorable for dissimilatory nitrate reduction to ammonia (DNRA). We present evidence for the microbial transformation of nitrite under anaerobic conditions, with potential geochemical and evolutionary importance. As nitrogen oxides were already present on early Earth, our finding presents the possibility of a nitrogen cycle before the evolution of oxygenic photosynthesis.

Effects of Polysaccharides From Auricularia auricula on the Immuno-Stimulatory Activity and Gut Microbiota in Immunosuppressed Mice Induced by Cyclophosphamide.

Recently, the immuno-enhancing potential of polysaccharide from Auricularia auricula (AAP) has been an area of research interest. However, the immune-stimulatory activity and mechanisms of AAP in immunosuppressive mice treated with cyclophosphamide (CTX) are still poorly understood. This study aimed to evaluate the immuno-enhancing effects of AAP and mine its possible mechanisms. Firstly, polysaccharides were isolated from A. auricula and purified. Secondly, the immune-stimulatory activities of the first AAP fraction (AAP1) were evaluated in the CTX-treated mice. Results showed that AAP1 significantly enhanced immune organ indexes, remarkably stimulated IFN-γ, IL-2, IL-4, IL-10, and TNF-α levels in the serum, and dramatically up-regulated the mRNA levels of Claudin-1, Occludin and ZO-1. Compared to the CTX group, AAP1 administration restored the gut microbiota composition similar to that of the control group by decreasing the ratio of Firmicutes/Bacteroidetes and increasing the relative abundances of short-chain fatty acid-producing microbiota. This study provides useful information for its further application as an immune-stimulator in foods and drugs.