Suhang Wang,Jiaqing Liang,Yongkai Liao,Haixuan Zhou,Brian J. Reid,Chao Cai
The biodegradation of polycyclic aromatic hydrocarbons (PAHs) involves complex metabolic interactions among multiple degradation pathways. However, how interactions among different pathways influence the overall degradation efficiency remains poorly understood. In this study, Pseudoxanthomonas sp. G3, an efficient degrader of phenanthrene (PHE) and pyrene (PYR), was used to investigate pathway interactions under mixed-PAH conditions. Genomic and metabolomic analyses revealed that strain G3 degrades PHE and PYR through three pathways: the phthalate pathway (with phthalic acid as the dead-end product), a shared catechol degradation pathway, and the benzoate degradation pathway. Notably, PYR induced the benzoate degradation pathway, representing a previously unreported metabolism of PYR by bacteria. Integrated analyses revealed that PHE inhibits PYR degradation via dual mechanisms. Specifically, PHE preferentially utilizes the PYR-induced benzoate degradation pathway, thereby diverting metabolic flux and impeding PYR degradation. Moreover, the benzoate degradation pathway further inhibits the catechol degradation pathway, intensifying suppression of PYR degradation. These findings elucidate mechanistic insights into the interactions among the biodegradation pathways under mixed-PAH stress and provide a theoretical basis for targeted improvement of the efficiency and predictability of mixed-PAH degradation.
The traditional biological denitrification process has the problems of low removal rates and lack of a carbon source when treating wastewater with high ammonia nitrogen concentration and a low carbon–nitrogen ratio. Based on a bio-electrochemical system (BES), a novel carbon cloth bipolar plate multicompartment electroenhanced bioreactor (CBM-EEB) system was constructed. In this study, nitrogen removal efficiency and enrichment of functional bacteria using CBM-EEB under different voltage conditions were investigated. The results from next-generation sequencing indicated that the CBM-EEB included heterotrophic nitrification and aerobic denitrification (HNAD) and was dominated by heterotrophic nitrification aerobic denitrifying bacteria (HNADB). The applied voltage was confirmed as having the ability to regulate the microbial community structure and abundance of functional genes, thereby further enhancing the nitrogen removal efficiency of the system. The total nitrogen removal efficiency was 77.70 ± 1.14, 87.10 ± 0.56, 86.40 ± 0.59, and 89.30 ± 0.53% under applied voltages of 0.4, 0.7, 1.0, and 1.3 V, respectively. All values were significantly higher than the control group (62.86 ± 2.06%). HNADB had the highest abundance among the 17 detected genera related to nitrogen metabolism. Facultative denitrifying bacteria, Pseudoxanthomonas, along with key bacteria of HNADB, such as Flavobacterium, constructed a shortcut simultaneous nitrification–denitrification (SND) process. Poisson analysis and redundancy analysis (RDA) showed that the applied voltage improved the denitrification efficiency by changing the microbial community structure, reducing the abundance of heterotrophic bacteria, and increasing the unit abundance of key functional genes so that less organics were required for the denitrification process. The increased nitrogen removal efficiency in the experimental group was mainly related to simultaneous nitrification–denitrification process and cooperation of microbial communities in the anode and the cathode. This study highlighted the feasibility of CBM-EEB to enhance the HNAD reaction and the response of wastewater with a low C/N ratio to enhance the abundance of microbial bacteria and their functional gene abundance.
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