Towards a standardized protocol for studying chemolithoautotrophic denitrification with pyrite at circumneutral pH

摘要

Laboratory studies on chemolithoautotrophic microbial denitrification coupled to pyrite oxidation at circumneutral pH yielded conflicting results. Some studies indicated that microbial oxidation of pyrite does occur, but several reports have shown that no microbial pyrite oxidation took place in experiments with pyrite as electron donor and nitrate as electron acceptor. We propose that inconsistent experimental and analytical protocols may cause substantial uncertainty in the interpretation of results from such laboratory studies, and may even produce artifacts. In this study, a comprehensive overview of possible pitfalls and artifacts in relation to geochemical and microbiological interferences is provided. Key interferences are impurities of reduced sulfur species associated with pyrite, interferences of nitrite and dissolved Fe(III) with quantitative spectrophotometric determination of Fe(II) and Fe(III) during acidic extractions, interference of oxygen, occurrence of residual iron and sulfur compounds in the reaction medium, and interference of cell-associated and stored sulfur. Therefore, we propose a series of experimental standard protocols to overcome these interferences in future studies on chemolithoautotrophic denitrification with pyrite.