Magnetite Formation During Microbial Dissimilatory Iron Reduction

Abstract

Magnetite appears to be p~Ocuced concurrently with the oxidation of organic matter coupled to Fe(III) reduction in a number of anaerobic sedimentary environments (Perry et al., 1973; Baur et al., 1985; Walker, 1984; Elmore et al., 1986; McCabe et al., 1987; Karlin et al., 1987; Lovley and Reynolds, 1987; Ponamperuma, 1972). The preponderance of evidence indicates that, at the pH, temperature, and pressure of most sedimentary environments, most of the Fe(III) reduction is the result of enzymatic reduction of Fe(III) by microorganisms (Kamura et al., 1963; S0rensen, 1982; Munch and Ottow, 1983; Jones et al., 1983; Lovley and Phillips, 1986a; Lovley et al., 1988). However, dissimilatory Fe(III)-reducing microorganisms which can effectively couple the oxidation of organic compounds to the reduction of Fe(III) were only recently described (Lovley et al., 1987; Lovley and Phillips, 1988; Lovley et al., 1989a; Lovley et al., 1989c). During the initial studies with these Fe (III)-reducing organisms it was discovered that ultrafinegrained magnetite is an endproduct of dissimilatory Fe(III) reduction. This chapter describes the metabolism of these newly discovered dissimilatory Fe (II I)-reducing bacteria and discusses the implications of their metabolism for the formation and dissolution of magnetite in sedimentary environments.