Aerobic Methanotrophs Grew Under Anoxic Conditions and Supported a Diverse Heterotrophic Bacterial Community

Methanotrophy has become a promising process for biotechnological applications. The initial goal of this study was to investigate methanotrophic denitrification as an alternative to nitrogen removal in waters that have a low organic content. Sequencing batch reactors (SBRs) were inoculated with a blend of marine and mangrove sediments (Sed-SBR), or anaerobic granular sludge from a upflow anaerobic sludge bed reactor treating poultry slaughterhouse wastewater (AnS-SBR) immobilized in polyurethane foams under anoxic conditions. Methane was provided as the sole external electron donor and organic carbon source. Methane supported denitrification to a small extent (<2.0mg N.g total volatile solids(-1) d(-1)) and supported biomass growth for the AnS-SBR in 10% of the initial volatile suspended solids. DNA sequencing of initial inocula showed high richness and low dominance for Sed inoculum, while the most abundant microorganisms in AnS inoculum were chemoorganotrophs typically found in anaerobic environments. In initial inocula, reads belonging to methanotrophs accounted for <0.5% of the sample. In enriched samples, aerobic methanotrophic organisms (especially those affiliated with the genera Methylomonas) were the only organisms found, which are capable of oxidizing methane, accounting for nearly 5% of the relative abundance, while there was a decay of initially abundant organisms. Various heterotrophic groups were also identified, indicating that methanotrophs allowed the establishment of a diverse community, even under adverse environmental conditions. These results suggest aerobic methanotrophs are versatile under anoxic conditions and that it is a widespread phenomenon, since it was observed for both inocula tested.