Deep subsurface microbial processes

Abstract

Information on the microbiology of the deep subsurface is necessary in order to understand the factors controlling the rate and extent of the microbially catalyzed redox reactions that influence the geophysical properties of these environments. Furthermore, there is an increasing threat that deep aquifers, an important drinking water resource, may be contaminated by man's activities, and there is a need to predict the extent to which microbial activity may remediate such contamination. Metabolically active microorganisms can be recovered from a diversity of deep subsurface environments. The available evidence suggests that these microorganisms are responsible for catalyzing the oxidation of organic matter coupled to a variety of electron acceptors just as microorganisms do in surface sediments, but at much slower rates. The technical difficulties in aseptically sampling deep subsurface sediments and the fact that microbial processes in laboratory incubations of deep subsurface material often do not mimic in situ processes fre-quently necessitate that microbial activity in the deep subsurface be inferred through nonmicrobiological analyses of ground water. These approaches include measurements of dissolved H2, which can predict the predominant microbially catalyzed redox reactions in aquifers, as well as geochemical and groundwater flow modeling, which can be used to estimate the rates of microbial processes. Microorganisms recovered from the deep subsurface have the potential to affect the fate of toxic organics and inorganic contaminants in groundwater. Microbial activity also greatly influences the chemistry of many pristine groundwaters and contributes to such phenomena as porosity development in carbonate aquifers, accumulation of undesirably high concentrations of dissolved iron, and production of methane and hydrogen sulfide. Although the last decade has seen a dramatic increase in interest in deep subsurface microbiology, in comparison with the study of other habitats, the study of deep subsurface microbiology is still in its infancy.However, it is becoming increasingly apparent that even in ancient, relatively nondynamic subsurface en-Copyright 1995 by the American Geophysical Union. 8755-1209/95/95 RG-01305 $15. O0 ß 365 ß Reviews of Geophysics, 33, 3 / August 1995 pages 365-381Paper number 95RG01305 366 ß Lovley and Chapelle-DEEP SURFACE MICROBIAL PROCESSES 33, 3 / REVIEWS OF GEOPHYSICS vironments, simplified nonbiological models do not accurately describe or predict important geochemical processes. For example, attempts to describe the distribution of redox reactions in groundwater with equilibrium thermodynamic models are generally unsuccessful [Fish, 1993;Hostettler, 1984; Lindberg and Runnells, 1984 ; Lovley et al., 1994, and references therein]. This is because most of these redox reactions do not take place spontaneously but require microorganisms to catalyze them. Microorganisms catalyze the redox reactions in order to gain energy for maintenance and growth. This requirement to conserve energy p...

Influence of dissimilatory metal reduction on fate of organic and metal contaminants in the subsurface

“…In general, the zone in which Fe(III) reduction predominates is found downgradient of zones of methane production and sulfate reduction, and upgradient of zones of nitrate and Mn(IV) reduction, as shown in Figure 1. The reason for this distribution is that methanogenesis and sulfate reduction can only become important TEAPs when microbial Fe(III) reduction becomes limited by the availability of Fe(III), whereas typically no net Fe(III) reduction occurs in the presence of Mn(IV) and nitrate (Lovley and Chapelle 1995).…”

“…Dissimilatory Fe(III) reduction significantly influences the fate of both organic and inorganic compounds in both pristine and contaminated subsurface environments. For example, in deep pristine aquifers Fe(III) reduction can be an important process for oxidation of organic matter, increasing the concentrations of dissolved inorganic carbon and dissolved Fe(II) while at the same time preventing the accumulation of sulfide Chapelle and Lovley 1992;Lovley and Chapelle 1995). These and other roles of dissimilatory Fe(III) reduction in pristine aquifers have recently been reviewed (Lovley and Chapelle 1995;Lovley 1997a) and are not discussed further here.…”

Microbial Fuel Cells, A Current Review

“…The oxidation and reduction process can be increased through the addition of Fe(III) chelators or electron shuttles [42][43][44] to promote increased transfer of electrons between cells and insoluble Fe(III) oxides. Contaminants often persist in the environment due to a lack of suitable electrons acceptors [45][46][47][48][49] and the addition of chelators, electron shuttles or other electron acceptors in the subsurface environment is not feasible. Pure cultures of Geobacter metallireducens are able to oxidize benzoate [1], and toluene [50] using an electrode as the final electron acceptor.…”

Laboratory evolution of Geobacter sulfurreducens for enhanced growth on lactate via a single-base-pair substitution in a transcriptional regulator

“…For example, lactate is a convenient electron donor for promoting anaerobic metabolism because it can be provided from onetime emplacements of slow-release formulations (Hazen and Tabak, 2005). In contrast to acetate, which is a major intermediate in carbon and electron flow in the subsurface, lactate is expected to be a minor constituent under conditions present during the stimulation of bioremediation in the subsurface (Lovley and Chapelle, 1995). Therefore, a consequence of adding high concentrations of this usually rare substrate may be an adaptive response to utilize lactate more effectively.…”