Heterotrophic nitrifiers are bacteria that aerobically oxidize ammonia in the presence of organic carbon sources, which differs from autotrophic nitrifiers that extract energy from ammonia oxidation for cell metabolism and growth. The physiological significance of heterotrophic ammonia oxidation remains unclear, even though this process has been known for decades. Here, we demonstrate that direct ammonia oxidation (Dirammox)—a heterotrophic ammonia oxidation process with dinitrogen (N₂) as the primary product—is associated with both redox balance and the electron transport chain in Alcaligenes faecalis. Genetic and proteomic studies indicated that disruption of Dirammox genes (dnfA/dnfB/dnfC) induces a transient redox imbalance and perturbation in energy metabolism, further resulting in delayed growth. In addition, we found via biochemical and physiological studies that endogenous reactive oxygen species (ROS) enhance redox fluxes to ammonia oxidation, and the genetic disruption of cytochrome c peroxidase results in an increased flux of electrons to ammonia oxidation, producing N₂ and N₂O. These unexpected findings provide a more thorough understanding of both the Dirammox process and the physiology of heterotrophic ammonia oxidation.

Contaminated sites from electronic waste (e-waste) dismantling and coking plants feature high concentrations of heavy metals (HMs) and/or polycyclic aromatic hydrocarbons (PAHs) in soil. Mixed contamination (HMs + PAHs) hinders land reclamation and affects the microbial diversity and function of soil microbiomes. In this study, we analyzed HM and PAH contamination from an e-waste dismantling plant and a coking plant and evaluated the influences of HM and PAH contamination on soil microbiomes. It was noticed that HMs and PAHs were found in all sites, although the major contaminants of the e-waste dismantling plant site were HMs (such as Cu at 5,947.58 ± 433.44 mg kg⁻¹, Zn at 4,961.38 ± 436.51 mg kg⁻¹, and Mn at 2,379.07 ± 227.46 mg kg⁻¹), and the major contaminants of the coking plant site were PAHs (such as fluorene at 11,740.06 ± 620.1 mg kg⁻¹, acenaphthylene at 211.69 ± 7.04 mg kg⁻¹, and pyrene at 183.14 ± 18.89 mg kg⁻¹). The microbiomes (diversity and abundance) of all sites were determined via high-throughput sequencing of 16S rRNA genes, and redundancy analysis was conducted to investigate the relations between soil microbiomes and contaminants. The results showed that the microbiomes of the contaminated sites divergently responded to HMs and PAHs. The abundances of the bacterial genera Sulfuritalea, Pseudomonas, and Sphingobium were positively related to PAHs, while the abundances of the bacterial genera Bryobacter, Nitrospira, and Steroidobacter were positively related to HMs. This study promotes an understanding of how soil microbiomes respond to single and mixed contamination with HMs and PAHs.

Previous study demonstrated that Ganoderma meroterpene derivative (GMD) increased the abundance of butyrate-producing bacteria in gut and subsequently delivered anti-metabolic disorder effect of host. To specify the key commensal bacteria associating with the beneficial effects, we tried to isolate and compare the microbiota from the cecal samples of GMD- and vehicle-treated ob/ob mice, and further identified butyrate-producing bacterial strains. It was found that Faeciroseburia intestinalis was enriched and 11 strains affiliated to F. intestinalis were cultivated from the gut of GMD-treated mice. In vitro assay attested butyrate production by representative strain of F. intestinalis. Oral administration with F. intestinalis further demonstrated its benefits on regulating hyperglycemia and hyperlipidemia, on decreasing plasma lipopolysaccharide (LPS) and inflammation, and on improving hepatic injuries. Treatment with F. intestinalis effectively enhanced the level of gut butyrate, which subsequently ameliorated the intestinal barrier function and activated epithelial PPAR-γ signaling pathway to regulate microbiome homeostasis in gut. Our study demonstrated that the causal relationship between the butyrate-producing bacteria and the GMD's therapeutic effects and confirmed the important function of the butyrate-producing F. intestinalis in maintaining host metabolism homeostasis.