Detection of Dissimilatory Iron-Reducing <i>Deltaproteobacteria</i> in Anaerobic Sludge with High Mineral Content

Abstract

Several species of dissimilatory iron-reducing Deltaproteobacteria (DIRD) have been isolated and studied worldwide; they have various applications in microbial fuel cells and in bioremediation strategies such as dissimilatory iron reduction. In this study, we detected DIRD in anaerobic sludge with a high mineral content (Na, K, Ca, and Fe) taken from an anaerobic tank at a landfill leachate treatment system (LLTS) and the first anaerobic filter chamber of an advanced Johkasou system that uses iron electrolysis (AJIE). Ferrihydrite media treated with LLTS or AJIE samples turned black and showed magnetic response. A bacterium closely related to Desulfuromonas palmitatis SDBY1 was found in the LLTS anaerobic sludge by PCR-denaturing gradient gel electrophoresis analysis after incubation. However, no single clear band derived from DIRD was found in the AJIE sample after incubation, although it produced magnetite. The number of DIRD in the anaerobic sludge was quantified by quantitative real-time PCR using a DIRD-specific primer set, and subsequently PCR amplicons derived from DIRD were detected in media containing the LLTS and AJIE samples. DNA sequence analysis of a PCR amplicon from the AJIE sample identified a bacterium closely related to Geobacter lovleyi SZ.