The occurrence of copious animal populations at deep-sea vents indicates an effective microbial chemosynthetic biocatalysis of hydrothermal fluids on their emission into oxygenated ambient seawater. The large metabolic and physiological diversity of microbes found at these sites, including anaerobic and aerobic hyperthermophiles, reflects an even higher variety of biocatalytic or enzymatic reactions that greatly influence deep-sea hydrothermal geochemistry.

Introduction

The extent of biocatalysis in geochemical transformations is still an enigmatic issue. Although it is well understood that processes such as microbial photosynthesis, sulphate reduction, denitrification, etc., do not occur in the absence of the responsible organisms, geochemists generally are often unclear as to the effectiveness of biocatalytic transformations, where they occur, where they cannot occur, and how can they be predicted. This dilemma is due, in part, to an incompatibility between quantitative approaches in geochemical and microbiological studies. The unexpected discovery of high chemosynthetic bacterial production of biomass near deep-sea vents has resulted in studies that led to the following clarifying remarks for geochemists on biocatalytic transformation of hydrothermal emissions.

The observations contain that certain reduced inorganic compounds may serve as biocatalytically utilizable ‘sources of energy’ wherever they occur under conditions that allow the production of enzymes through microbial growth. During the Earth's history, biochemical-physiological evolution has resulted in large numbers of biogeochemical processes that are mediated by a large microbial and, thereby, biocatalytic diversity.