The formation of manganese (Mn) oxides in modern day environments is commonly controlled through microbially-mediated processes, producing biogenic Mn(IV/III) (hydr)oxides that are highly reactive toward trace metals. In metal polluted systems (such as coal mine drainage remediation sites), Mn-oxidizing fungi often dominate the Mn-oxidizing microbial community, and therefore may play an important role in manganese remediation and manganese mineral formation in such sites. Laboratory studies of microbiological systems often use Good’s Buffers (such as HEPES, POPSO, MOBS, MES, etc.), but recent research indicates that some Good’s Buffers alter abiotic birnessite structures. It is common for the pH of solutions to drift substantially in laboratory samples with mycogenic Mn oxides due to the production of fungal exudates, therefore the use of pH buffers is experimentally important. This work explores the impact of eight pH buffers (five Good’s Buffers: MOBS, MOPS, POPSO, HEPES, and MES; two ‘natural’ buffers: carbonate and phosphate; one additional buffer: DGA) on Mn oxidation by the fungus <i>Paraconiothyrium sporulosum</i> AP3s5-JAC2a. Solution pH, sample growth, and aqueous Mn<sup>2+</sup> concentrations were tracked daily. SEM-EDS analyses were conducted on the samples to understand the extent of morphological alteration associated with each buffer. Three of the buffers, MOBS, POPSO, and HEPES displayed distinct Mn oxide precipitation behaviors, despite all maintaining a relatively similar pH. Phosphate and DGA buffers exhibited poor buffering capacities, with substantial pH drift that may have resulted in manganese oxide morphological changes and large biomass formations. Mn oxidation in the MOPS system most closely resembles that of the buffer-free sample, and therefore may prove to be a candidate for further study. This work demonstrates the variable effects of pH buffers on biogenic manganese oxides, underlining the sensitivity of these materials to solution chemistry.

Is there really a “good” buffer? Identifying nonreactive pH buffers for fungal manganese oxide research

ACS Spring Meeting 2021

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