Acido- and Thermophilic Microorganisms: Their Features, and the Identification of Novel Enzymes or Pathways

Abstract

Although many types of acidophilic bacteria have been identified, most of these only grow at normal temperatures. Few bacterial species have been identified as the acido- and thermophilic microorganisms. By contrast, numerous Archaea, including the phyla Crenarchaeota and Euryarchaeota, have been identified, growing under acidic conditions at over 80 °C. As model microorganisms with acido- and thermophilic features, the genus Sulfolobus was chosen to describe characteristics of the organisms themselves and the features of their gene products. The features of Sulfolobus, including the nonphosphorylated Entner-Doudoroff pathway for metabolism of glucose and Sulfolobus-specific ATPase enzymes, are described in the second part of this chapter. The genomic data from Sulfolobus provide information on the unique features of these microorganisms that would be undetectable by direct observation, e.g., the tRNA system, repetitive sequences, and predicted sulfur metabolic enzymes, among others. However, many enzymes catalyzing reactions in the general model pathway are not detected in the genomic data from S. tokodaii, which means that, by itself, genomic data is not sufficient to fully understand all the features of those microorganisms. Thus, the functional analyses of each gene product are required to fully understand the whole microorganism. Several enzymes with carbohydrates metabolic activity are mentioned in the third part of this chapter as examples of novel enzymes identified through traditional purification from cells. Also discussed is detection of unexpected activities of gene products not predicted from the genomic data through activity analysis.