Fermentative, Iron-Reducing, and Nitrate-Reducing Microorganisms

Abstract

This chapter focuses on the microbiology of heterotrophic fermentative bacteria, some of which are able to grow by using various electron acceptors such as elemental sulfur, thiosulfate, iron, and nitrate. Clearly, the geochemistry of the reservoirs, together with the mineralogy and the physicochemical conditions of the oil field waters, selects for the presence of specific types of microorganisms. This is true for conditions in oil reservoirs where temperatures commonly between 60 and 80°C affect the survival and/or growth of thermophilic and hyperthermophilic fermentative microorganisms. Mesophilic, thermophilic, and hyperthermophilic fermentative bacteria constitute an important microbial community of the oil field environment. Its physiological and phylogenetic traits were unique among the oil field fermentative isolates, as it used protein extracts such as peptones and amino acids but was unable to ferment sugars. Nitrate-reducing microorganisms from oil reservoirs are of increased interest due to the in situ use of nitrate by oil companies to decrease sulfide concentrations in oil fields. In addition to sulfate-reducing bacteria (SRB) and Methanoarchaea, fermentative bacteria with various metabolic abilities were recovered from oil reservoirs. The presence of both hydrogen and acetate in deep reservoirs may explain survival and/or growth of some thermophilic heterotrophs. Through fermentative and oxidative processes, thermophiles appear metabolically adapted to participate in the energy and carbon cycles of deep reservoirs as proposed by the researchers.