Effect of dissimilatory iron reduction and Carex DOM on Crreduction by Enterobacter sp. PY16 isolated from wetland soil

Environmental context: Dissimilatory iron reduction and Carex-produced dissolved organic matter (DOM) have an important influence on Cr(VI) reduction by the Fe(III)-reducing bacterium Enterobacter. The role of Carex DOM and ferrihydrite in the biotransformation of Cr(VI) by the bacterial isolate was investigated. The findings should help underpin the remediation and detoxification of chromium in anaerobic environments, and provide promising insights into the quaternary system of bacterium/Fe(III)/Cr(VI)/DOM. Rationale: FeIII oxides and organic matter are important factors influencing CrVI degradation in wetland soils. However, it remains unclear how they interact in anaerobic systems. Methodology: In this study, a strain of iron-reducing bacterium was isolated from Poyang Lake Wetland and identified as Enterobacter sp. PY16 (PY16) by PCR-16S-rDNA sequence analysis. Moreover, microbial reduction of FeIII/CrVI by PY16 and their mutual transformation in the quaternionic system of PY16/ferrihydrite/CrVI/dissolved organic matter (DOM, extracted from Carex cinerascens) were investigated. Results: The results showed that PY16 could directly participate in the reduction of ferrihydrite and CrVI. The rate of CrVI reduction decreased with the increase of initial CrVI concentration, while it was enhanced by 2.78-42.99% in the presence of ferrihydrite. Moreover, 15 mg L-1 CrVI was almost eliminated after 72 h and the content of FeII increased by 78.21 mg L-1 in the presence of DOM. Discussion: The fastest CrVI reduction rate occurred when ferrihydrite and DOM coexisted in the system, mainly because the promoting effect of DOM on ferrihydrite synergistically promoted CrVI reduction. DOM and FeII produced during the ferrihydrite reduction process served as electron shuttles that promoted CrVI reduction by a biochemical redox pathway. However, the electron transfer and donation capacity of DOMox/DOMred and FeIII/FeII in the reaction process still need to be further studied. Implications for future research: The results underscored the importance of FeIII oxides and DOM on microbial CrVI reduction, thus providing a valuable technique to remove and detoxify chromium in wetland soils.