Metabolic promiscuity from the deep subsurface: A story of Survival or Superiority

The Witwatersrand Supergroup is a 2.9-billion-year-old formation of low permeability sandstone and shale with minor volcanic units and conglomerates with an ambient rock temperature of approximately 60°C. Thermus scotoductus SA-01 was isolated from fissure water at a depth of 3.2 kmbls in a South African gold mine and it shows the ability to reduce a variety of heavy metals under anaerobic conditions. It has been postulated that such microorganisms could play an important role in nutrient and metal cycling within the subsurface. Recently, our studies indicate that the cycling of metals could also occur under aerobic conditions and not only by the action of redox active enzymes, but other diverse metabolic proteins as well. In this study the capability of specific proteins to interact with metals is elucidated. Using Thermus SA-01 and its now completed genome sequence, metal reduction is studied through classic proteomic- and genomic methods. Finally we identify thermostable enzymes responsible for the transformation of various metals (Iron, Chrome, Uranium, Gold, etc) and discuss that reduction occurs via the serendipitous action of enzymes with other primary physiological functions, some of which are classical catabolic enzymes and anabolic proteins. This paper discusses the use of a ubiquitous enzyme/protein performing more than one function, possibly detoxifying the environment and using moonlighting as resource to decrease cellular energy requirements rather than elaborate metabolism in the subsurface.