Significance of polysaccharides in microbial physiology and the ecology of hydrothermal vent environments

Abstract

Hyperthermophilic microorganisms (those with maximum growth temperatures of 90°C and above) are known to inhabit deep-sea hydrothermal vent environments and are suspected of being present in the associated subsurface biosphere. One characteristic of the growth physiology of many heterotrophic hyperthermophiles is the capacity to use complex polysaccharides (e.g., α- and β-linked glucans as well as non-glucan hemicellulases) as carbon and energy sources. Polysaccharides may also play an important ecological role in the deep-sea subsurface biosphere as the structural elements of biofilms harboring both heterotrophic and chemolithotrophic microorganisms, representing a range of growth temperatures. Genome sequence analysis of several hyperthermophiles indicates that the enzymatic machinery to synthesize and hydrolyze polysaccharides is present in this group of microorganisms. This is supported by the biochemical characteristics of glycosidases from hyperthermophiles in addition to the observation that several hyperthermophiles form biofilms in pure and co-culture. It remains to be seen if biofilms form the basis for a subsurface biosphere but this possibility seems likely given the physiological characteristics of several hyperthermophiles and mesophiles, representative of microorganisms previously isolated from vent sites.