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

Biodegradable polylactic acid plastic can aid to achieve partial nitrification/denitrification for low carbon to nitrogen ratio wastewater treatment: Performance and microbial mechanism

The partial nitrification/denitrification (PND) process is a green biotechnology for nitrogen removal in low carbon to nitrogen ratio wastewater, however, inhibiting nitrite-oxidizing bacteria (NOB) remains a challenge. This study uncovered that polylactic acid (PLA) can eliminate NOB and regulate the structure and function of nitrogen-transforming bacteria (NTB). An anoxic/aerobic membrane bioreactor with PLA achieved a total nitrogen removal efficiency of 64.8%, much higher than the 32.4% without PLA. Nitrite accumulation during nitrification stage reached 66.7% with PLA addition. Ammonia-oxidizing bacteria were transiently inhibited by PLA but recovered quickly. NOB were maintained at low levels due to the absence of genes for protein and DNA repair, while denitrifiers lacking NarGHI/NapAB genes were enriched. OLB8, with a relative abundance of 13.7%, played a central role in regulating NTB interaction and facilitating PND. In summary, this study provided a new strategy for improving nitrogen removal from wastewater through the reuse of PLA plastics.

Hydrazine promoted nitrite reduction in partial-denitrification by enhancing organic-substrate uptake and electron transport

Partial denitrification coupled with anammox is a promising approach for sustainable nitrogen removal from wastewater. However, this coupling can be influenced by hydrazine (N2H4) released by anammox bacteria. This study aimed to reveal how N2H4 regulates partial denitrification. Short-term batch experiments showed that 0.5 to 10 mg N/L of N2H4 promoted nitrite (NO2-) accumulation, likely by inhibiting the electron transfer from cyt c to nitrite reductase. However, long-term exposure to N2H4 (0.5 and 1 mg N/L) shifted the microbial community and increased NO2- reduction. This exposure enriched the genera OLB8, Thauera, and f_Rhodocyclaceae, and increased the abundance of genes involved in EPS formation, substrate transport and electron transport. The long-term outcome was more NO2- reduction to N2 and more substrate (COD) oxidation. While N2H4 benefits NO2- accumulation in short-term, the mechanism is not sustainable, highlighting the importance of minimizing N2H4 release for successful in such coupled nitrogen removal systems.

Anaerobic stabilization and landscape utilization of rural sewage sludge from the enhanced membrane coagulation process

In this study, enhanced membrane coagulation (EMC) sludge was subjected to various alkaline (pH 7.2, 10, and 11), temperature (35 °C and 55 °C), and duration (0.5 h and 1 day) pretreatment conditions before being inoculated into biogas reactors operated for 176 days. Optimal pretreatment (pH 11, 55 °C, and 1 day) effectively hydrolyzed particulate COD to SCOD (8435 ± 121 mg/L). Higher pH levels also facilitated the dissolution of amphoteric aluminum-phosphorus (Al-P) compounds, enhancing phosphorus release (91.8 mg/L) from the sludge. This alkaline pretreatment, especially under optimal conditions, significantly increased biogas production and methane concentrations in long-term semi-continuous anaerobic digesters, with methane yields of 188.4 mL/gVS. The microbial community structure in all three reactors exhibited similar shifts, with saccharolytic and proteolytic fermentative bacteria dominating early stages and Thermovirga and an uncultured bacterium (Run-SP154) prevalent in later stages. Methanothrix, an acetotrophic methanogen, dominated the archaeal community in the inoculum (>91 %) and remained prominent (>40 %) throughout the experiment, while hydrogenotrophic methanogens from the genus Methanolinea increased over time, accounting for >24 % of the sequences in the final stages. Additionally, the feasibility of using EMC digestate as fertilizer for mulberry plants was tested, showing that digestate from optimally pretreated sludge promoted better growth than conventional chemical fertilizers. This suggests that this approach is a promising method for decentralized sewage treatment systems.

Lactobacillus crispatus-Mediated Gut-Reproductive Tract Axis-Alleviated Microbial Dysbiosis and Oviductal Inflammation in a Laying Hen Model

Oviductal inflammation (OI) significantly reduces the egg production and economic returns in poultry farming. While Lactobacillus crispatus (LAC) is effective against inflammation, its role in treating or preventing oviductal inflammation is understudied. In this study, we investigated the therapeutic mechanisms of LAC on oviductal inflammation, with a focus on reproductive tract health, microbiome, gene expression, and cytokine levels. This study involved 24 Jingfen No. 6 laying hens aged 60 weeks, divided into four groups: the CON, OI, OI + LAC, and OI + heat-killed Lactobacillus crispatus (HLAC) groups. And it included a 10-day adaptation, a 7-day period for the development of OI using inflammation-inducing drugs (the control received saline), followed by an 8-day treatment in which the CON and OI groups received 1 mL of MRS broth daily, and the OI + LAC and OI + HLAC groups were treated with live and heat-killed Lactobacillus crispatus (109 CFUs/mL), respectively, with six hens in each group. This study showed that Lactobacillus crispatus supplementation significantly reduced the oviductal inflammation and atrophy in the hens, with the affected hens showing markedly lower egg production rates (p < 0.001) compared to the control and treated groups (OI + HLAC and OI + LAC). The daily intake of fresh (OI + LAC, p = 0.076) or heat-killed (OI + HLAC, p < 0.01) Lactobacillus crispatus notably enhanced the feed conversion efficiency. The OI group suffered significant ovarian damage and vascular rupture, more so than the CON group, while Lactobacillus crispatus supplementation mitigated this damage. The IL-1β, IL-6, and IL-8 levels were significantly elevated in the OI group compared to those in the OI + LAC group (p < 0.05), with a significant reduction in the TNF-α levels in the latter (p < 0.001). The supplementation improved the microbial composition in the cecum, isthmus, and shell gland, enriching the cecum with beneficial bacteria, such as Ruminococcus_torques_group and Megamonas. This approach fostered ovarian health and follicle differentiation and preserved the epithelial cell barrier function in the shell gland, reducing inflammatory damage in the genital tract. This dual efficacy underscores the role of the probiotic in diminishing oviductal inflammation, regardless of its state.

Metabolomic reveals the responses of sludge properties and microbial communities to high nitrite stress in denitrifying phosphorus removal systems

Nitrite, as an electron acceptor, plays a good role in denitrifying phosphorus removal (DPR); however, high nitrite concentration has adverse affects on sludge performance. We investigated the precise mechanisms of responses of sludge to high nitrite stress, including surface characteristics, intracellular and extracellular components, microbial and metabolic responses. When the nitrite stress reached 90 mg/L, the sludge settling performance was improved, but the activated sludge was aging. FTIR and XPS analysis revealed a significant increase in the hydrophobicity of the sludge, resulting in improve settling performance. However, the intracellular carbon sources synthesis was inhibited. In addition, the components in the tightly bound extracellular polymeric substances (TB-EPS) of sludge were significantly reduced and indicated the disturb of metabolism. Notably, Exiguobacterium emerged as a new genus when face high nitrite stress that could maintaining survival in hostile environments. Moreover, metabolomic analysis demonstrated strong biological response to nitrite stress further supported above results that include the inhibited of carbohydrate and amino acid metabolism. More importantly, some lipids (PS, PA, LysoPA, LysoPC and LysoPE) were significantly upregulated that related enhanced membrane lipid remodeling. The comprehensive analyses provide novel insights into the high nitrite stress responses mechanisms in activated sludge systems.

Allelochemicals-mediated interaction between algae and bacteria: Direct and indirect contact

Secondary metabolites with bioactivity are allelochemicals. This study adopted direct contact (R0) and indirect contact (separated by 0.45 µm membrane, R1-A for algae, R1-S for sludge) to reveal the role of metabolites especially allelochemicals on interaction of bacteria and algae. Direct contact exhibited better nutrients removal than indirect contact, due to less antibacterial allelochemicals and oxidative stress. Bacterial signaling molecules were not detected. The major algae-derived allelochemicals were 13-Docosenamide, 9-Octadecenamide, n-Hexadecanoic acid, erucic acid, octadecanoic acid, β-sitosterol, and E,E,Z-1,3,12-Nonadecatriene-5,14-diol. Furthermore, presence of 13-Docosenamide and 9-Octadecenamide was associated with succession of Flavobacterium and suppression of nitrifying bacteria (Nitrosomonas, Ellin6067, and Nitrospira). Direct contact stimulated denitrifying bacteria Saccharimonadales and algae Scenedesmus, whereas indirect contact is friendly to Dechloromonas, Competibacter, nitrifying bacteria, algae Desmodesmus and Dictyosphaerium. This study highlights the essentiality of cell contact of bacteria-algae in establishing synergy, as cell contact mitigates antagonistic effect induced by metabolites.