Microbial bioremediation of produced water under different redox conditions in marine sediments

Electro-stimulation modulates syntrophic interactions in methanogenic toluene-degrading microbiota for enhanced functionality

Syntrophy achieved via microbial cooperation is vital for anaerobic hydrocarbon degradation and methanogenesis. However, limited understanding of the metabolic division of labor and electronic interactions in electro-stimulated microbiota has impeded the development of enhanced biotechnologies for degrading hydrocarbons to methane. Here, compared to the non-electro-stimulated methanogenic toluene-degrading microbiota, electro-stimulation at 800 mV promoted toluene degradation and methane production efficiencies by 11.49 %-14.76 % and 75.58 %-290.11 %, respectively. Hydrocarbon-degrading gene bamA amplification and metagenomic sequencing analyses revealed that f_Syntrophobacteraceae MAG116 may act as a toluene degrader in the non-electro-stimulated microbiota, which was proposed to establish electron syntrophy with the acetoclastic methanogen Methanosarcina spp. (or Methanothrix sp.) through e-pili or shared acetate. In the electro-stimulated microbiota, 37.22 ± 4.33 % of Desulfoprunum sp. (affiliated f_Desulfurivibrionaceae MAG10) and 58.82 ± 3.74 % of the hydrogenotrophic methanogen Methanobacterium sp. MAG74 were specifically recruited to the anode and cathode, respectively. The potential electrogen f_Desulfurivibrionaceae MAG10 engaged in interspecies electron transfer with both syntroph f_Syntrophobacteraceae MAG116 and the anode, which might be facilitated by c-type cytochromes (e.g., ImcH, OmcT, and PilZ). Moreover, upon capturing electrons from the external circuit, the hydrogen-producing electrotroph Aminidesulfovibrio sp. MAG60 could share electrons and hydrogen with the methanogen Methanobacterium sp. MAG74, which uniquely harbored hydrogenase genes ehaA-R and ehbA-P. This study elucidates the microbial interaction mechanisms underlying the enhanced metabolic efficiency of the electro-stimulated methanogenic toluene-degrading microbiota, and emphasizes the significance of metabolic and electron syntrophic interactions in maintaining the stability of microbial community functionality.

Aerobic biodegradation of quinoline under denitrifying conditions in membrane-aerated biofilm reactor

Aerobic denitrification is being investigated as a novel biological nitrogen removal process, yet the knowledge on aerobic denitrification is limited to pure culture isolations and its occurrence in bioreactors remains unclear. This study investigated the feasibility and capacity of applying aerobic denitrification in membrane aerated biofilm reactor (MABR) for biological treatment of quinoline-laden wastewater. Stable and efficient removals of quinoline (91.5 ± 5.2%) and nitrate (NO₃^-) (86.5 ± 9.3%) were obtained under different operational conditions. Enhanced formation and function of extracellular polymeric substances (EPS) were observed at increasing quinoline loadings. MABR biofilm was highly enriched with aerobic quinoline-degrading bacteria, with a predominance of Rhodococcus (26.9 ± 3.7%) and secondary abundance of Pseudomonas (1.7 ± 1.2%) and Comamonas (0.94 ± 0.9%). Metagenomic analysis indicated that Rhodococcus contributed significantly to both aromatic degradation (24.5 ± 21.3%) and NO₃^- reduction (4.5 ± 3.9%), indicating its key role in aerobic denitrifying quinoline biodegradation. At increasing quinoline loadings, abundances of aerobic quinoline degradation gene oxoO and denitrifying genes of napA, nirS and nirK increased; there was a significant positive correlation of oxoO with nirS and nirK (p < 0.05). Aerobic quinoline degradation was likely initiated by hydroxylation, encoded by oxoO, followed by stepwise oxidations through 5,6-dihydroxy-1H-2-oxoquinoline or 8-hydroxycoumarin pathway. The results advance our understanding of quinoline degradation during biological nitrogen removal, and highlight the potential implementation of aerobic denitrification driven quinoline biodegradation in MABR for simultaneous removal of nitrogen and recalcitrant organic carbon from coking, coal gasification and pharmaceutical wastewaters.

Sustained-release nitrate combined with microbial fuel cell: A novel strategy for PAHs and odor removal from sediment

Nitrate addition is a biostimulation technique that can improve both the oxidation of acid volatile sulfide (AVS) through autotrophic denitrification and the biodegradation of polycyclic aromatic hydrocarbons (PAHs) via heterotrophic denitrification. However, during the remediation, parts of the dissolved nitrate in the sediment migrates from the sediment to the overlying water, leading to the loss of effective electron acceptor. To overcome this limitation, a combined approached was proposed, which involved nitrocellulose addition and a microbial fuel cell (MFC). Results indicated the nitrate could be slowly released and maintained at a higher concentration over long term. In the combined system, the removal efficiencies of PAHs and AVS were 71.56% and 89.76%, respectively. Furthermore, the voltage attained for the MFC-nitrocellulose treatment was maintained at 146.1 mV on Day 70, which was 5.37 times higher than that of the MFC-calcium nitrate treatment. Sediments with nitrocellulose resulted in lower levels of nitrate and ammonium in the overlying water. Metagenomic results revealed that the combined technology improved the expression of nitrogen-cycling genes. The introduction of MFC inhibited sulfide regeneration during incubation by suppressing the enzyme activity like EC4.4.1.2. The enhanced biostimulation provided potential for in-situ bioremediation utilizing MFC coupled with slow-released nitrate (i.e., nitrocellulose) treatment.