Novel Insight into Microbially Mediated Nitrate-Reducing Fe(II) Oxidation by <i>Acidovorax</i> sp. Strain BoFeN1 Using Dual N–O Isotope Fractionation
Dandan Chen, Kuan Cheng, Tongxu Liu, Guojun Chen, Andreas Kappler, Xiaomin Li, Raymond Jianxiong Zeng, Yang Yang, Fujun Yue, Shiwen Hu, Fang Cao, Fangbai Li
Abstract
Microbially mediated nitrate reduction coupled with Fe(II) oxidation (NRFO) plays an important role in the Fe/N interactions in pH-neutral anoxic environments. However, the relative contributions of the chemical and microbial processes to NRFO are still unclear. In this study, N–O isotope fractionation during NRFO was investigated. The ratios of O and N isotope enrichment factors ( 18 ε: 15 ε)-NO 3 – indicated that the main nitrate reductase functioning in Acidovorax sp. strain BoFeN1 was membrane-bound dissimilatory nitrate reductase (Nar). N–O isotope fractionation during chemodenitrification [Fe(II) + NO 2 – ], microbial nitrite reduction (cells + NO 2 – ), and the coupled process [cells + NO 2 – + Fe(II)] was explored. The ratios of ( 18 ε: 15 ε)-NO 2 – were 0.58 ± 0.05 during chemodenitrification and −0.41 ± 0.11 during microbial nitrite reduction, indicating that N–O isotopes can be used to distinguish chemical from biological reactions. The ( 18 ε: 15 ε)-NO 2 – of 0.70 ± 0.05 during the coupled process was close to that obtained for chemodenitrification, indicating that chemodenitrification played a more important role than biological reactions during the coupled process. The results of kinetic modeling showed that the relative contribution of chemodenitrification was 99.3% during the coupled process, which was consistent with that of isotope fractionation. This study provides a better understanding of chemical and biological mechanisms of NRFO using N–O isotopes and kinetic modeling.