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

Rationale. Fe-III oxides and organic matter are important factors influencing Cr-VI 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 Fe-III/Cr-VI by PY16 and their mutual transformation in the quaternionic system of PY16/ ferrihydrite/ Cr-VI/ 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 Cr-VI. The rate of Cr-VI-reduction decreased with the increase of initial Cr-VI concentration, while it was enhanced by 2.78-42.99% in the presence of ferrihydrite. Moreover, 15 mg L- 1 Cr-VI 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 Cr-VI reduction rate occurred when ferrihydrite and DOM coexisted in the system, mainly because the promoting effect of DOM on ferrihydrite synergistically promoted Cr-VI reduction. DOM and Fe-II produced during the ferrihydrite reduction process served as electron shuttles that promoted Cr-VI reduction by a biochemical redox pathway. However, the electron transfer and donation capacity of DOMox/DOMred and Fe-III/Fe-II in the reaction process still need to be further studied. Implications for future research. The results underscored the importance of Fe-III oxides and DOM on microbial Cr-VI reduction, thus providing a valuable technique to remove and detoxify chromium in wetland soils.