Adaptive evolutionary strategies of microbes to manganese in nitrogen-culturing sludge

Human activities have significantly increased the accessibility of nitrogen and manganese, which has had an impact on the evolution of microorganisms. To investigate the effect of increasing manganese accessibility on microbial nitrogen cycle, Mn-HA (Manganese-Humus chelates), a naturally occurring compound in the form of organochelate, was introduced into the conventional nitrification-denitrification process. The findings revealed that the addition of Mn-HA significantly facilitated the removal of ammonium and nitrate potentially by Mnammox (anaerobic ammonium oxidation mediated by Mn (IV)-oxide reduction) and Mn-based autotrophic denitrification. Metagenomic analyses suggested the presence of manganese-redox microorganisms involved in nitrification and denitrification, indicating the occurrence of manganese redox-coupled nitrogen metabolism processes. Additionally, the production and consumption of bio-MnOx (bio-Manganese Oxides) were observed in conjunction with denitrification and nitrification. The production of unequal amounts of bio-MnOx suggested that bio-MnOx may have been deposited in the sediment. This was confirmed by the BCR sequential extraction experiment. Coupling Mn metabolism with N metabolism is an adaptive strategy for nitrogen metabolizing microorganisms. For Mn-sensitive populations, they gain respite from Mn-rich environments by adopting strategies such as manganese oxidation, regulating manganese transport, pumping out intracellular manganese and evolving other manganese resistance genes.