Inactivation of Escherichia coli enhanced by anaerobic microbial iron reduction

Lavane Kim,Van Toan Pham,Tao Yan

doi:10.1007/s11356-020-11209-w

Abstract

Microbial iron reduction (MIR) is an important and ubiquitous natural process in the biogeochemical cycling of iron and carbon in anaerobic sedimentary and subsurface environments. The objectives of this study were (1) to determine if the MIR process can enhance the inactivation of Escherichia coli cells under anaerobic conditions and (2) to identify potential inactivation mechanisms. Laboratory microcosm experiments showed that the presence of MIR activity significantly enhanced E. coli inactivation, and the inactivation rate under the MIR condition was significantly larger than those under other anaerobic redox conditions. Under anoxic condition, higher Fe2+concentrations exhibited a linear function to larger E. coli inactivation rates, indicating that the production of Fe2+by MIR was one of the important roles in E. coli inactivation. When E. coli cells were amended as the sole electron source to the MIR process, increased Fe2+ production was observed, which corresponded to decreasing TOC concentration. Together, the results suggest that MIR enhanced E. coli inactivation through the production of Fe2+ as metabolic waste, and the inactivation benefited the MIR process as the inactivated cells were used as an electron source, which represents a potential new mechanism for bacterial inter-species competition. This knowledge could further improve our understanding of the fate of fecal bacteria in natural environments where the MIR process is prevalent, and may also be explored for enhanced removal of bacterial pathogens in engineering processes.

Highlights

Microbial iron reduction (MIR) is an important and ubiquitous natural process in the biogeochemical cycling of iron and the oxidation of organic matter in anaerobic sedimentary and subsurface environments (Lovley 1991)
The objectives of this study were (1) to determine if MIR process can enhance the inactivation of the model organism Escherichia coli under anaerobic conditions and (2) to identify potential inactivation mechanisms
The impact of MIR on the inactivation of E. coli cells was investigated by comparing the decay patterns of E. coli cells in the active MIR microcosms, which received the anaerobic inoculum, to those in the control microcosms, which did not receive the anaerobic inoculum

Summary

Introduction

Microbial iron reduction (MIR) is an important and ubiquitous natural process in the biogeochemical cycling of iron and the oxidation of organic matter in anaerobic sedimentary and subsurface environments (Lovley 1991). Reducing bacteria (IRBs), which use Fe(III) as the terminal electron acceptor in respiration, is considered the most important mechanism in converting Fe(III) to Fe(II)aq (Lovley 1991; Weber et al 2006). During the MIR process, IRBs can oxidize and mineralize a large variety of organic compounds and produce CO2 (Lovley et al 1989; Lovley and Lonergan 1990; Lovley et al 1992; Lu et al 2008), which plays a major role in carbon cycling in anaerobic environments (Lovley 1991). Since the initial isolation of Shewanella and Geobacter species (Lovley and Phillips 1988; Obuekwe et al 1981), our knowledge about the phylogenetic diversity of IRBs has greatly expanded to include many species across the domain Bacteria (Lonergan et al 1996; Lovley 2006), further reflecting the ubiquity of the MIR process in the environment.

Objectives

Methods

Results