Distinctive species interaction patterns under high nitrite stress shape inefficient denitrifying phosphorus removal performance.

Denitrifying phosphorus removal using nitrite as an electron acceptor is an innovative, resource-efficient approach for nitrogen and phosphorus removal. However, the inhibitory effects of nitrite on anoxic phosphorus uptake and process stability are unclear. This study investigated the total phosphorus removal performance under nitrite stress and analyzed microbiome responses in 186 sludge samples. The results indicated that the total phosphorus removal rates and dominant taxon abundance were highly similar under nitrite stress. High nitrite stress induced a community-state shift, leading to unstable dynamics and decreased total phosphorus removal. This shift resulted from increased species cooperation. Notably, the shared genera OLB8 and Zoogloea under non-inhibitory nitrite stress, suggesting their vital roles in mitigating nitrite stress by enhancing carbon and energy metabolism. The response patterns of these bacterial communities to high nitrite stress can guide the design and optimization of high-nitrogen wastewater reactors.

Purification, Identification, Chelation Mechanism, and Calcium Absorption Activity of a Novel Calcium-Binding Peptide from Peanut (Arachis hypogaea) Protein Hydrolysate.

A novel calcium-binding peptide was purified from peanut protein hydrolysate using gel filtration chromatography and identified using HPLC-MS/MS. Its amino acid sequence was determined as Phe-Pro-Pro-Asp-Val-Ala (FPPDVA, named as FA6) with the calcium-binding capacity of 15.67 ± 0.39 mg/g. Then, the calcium chelating characteristics of FPPDVA were investigated using ultraviolet-visible absorption spectroscopy, fluorescence spectroscopy, Fourier transform infrared spectroscopy, particle size, and zeta potential. The results showed that FPPDVA interacted with calcium ions, the chelation of calcium ions induced FPPDVA to fold and form a denser structure, the calcium-binding sites may mainly involve oxygen atoms from the carboxyl residues of Asp and Ala, and Phe possessed contact energy and carbonyl residues of Val. Microstructure analysis showed that FPPDVA-calcium chelate exhibited a regularly ordered and tightly aggregated sheets or block structures. Additionally, FPPDVA-calcium chelate had good gastrointestinal digestive stability and thermal stability. The results of everted rat intestinal sac and Caco-2 cell monolayer experiments showed that FPPDVA-calcium chelate could promote calcium absorption and transport through the Cav1.3 and TRPV6 calcium channels. These data suggest that FPPDVA-calcium chelate possesses the potential to be developed and applied as calcium supplement.