ABSTRACT
Various microorganisms, including prokaryotes and eukaryotes, contribute actively to certain geological processes, a fact that until not too long ago seems not always to have been suf- ciently appreciated by some microbiologists and geologists. Geomicrobially active prokaryotes
include members of the domain bacteria (formerly designated Eubacteria) and the domain archaea (formerly known as Archaebacteria and Archaeobacteria). Both bacteria and archaea are prokaryotes because they lack a true nucleus. Each has its genetic information encoded in a large circular polymeric molecule of deoxyribonucleic
7.1 Types of Geomicrobial Agents / 129 7.2 Geomicrobially Important Physiological Groups of Prokaryotes / 131 7.3Role of Microbes in Inorganic Conversions in the Lithosphere and Hydrosphere / 132 7.4Types of Microbial Activities Inuencing Geological Processes / 133 7.5Microbes as Catalysts of Geochemical Processes / 134
7.5.1Catabolic Reactions: Aerobic Respiration / 134 7.5.2Catabolic Reactions: Anaerobic Respiration / 137 7.5.3Catabolic Reactions: Respiration Involving Insoluble Inorganic Substrates as
Electron Donors or Acceptors / 138 7.5.4Catabolic Reactions: Fermentation / 140 7.5.5How Energy Is Generated by Aerobic and Anaerobic Respirers and by Fermenters
during Catabolism / 141 7.5.6How Chemolithoautotrophic bacteria (Chemosynthetic Autotrophs) Generate
Reducing Power for Assimilating CO2 and Converting It to Organic Carbon / 143 7.5.7 How Photosynthetic Microbes Generate Energy and Reducing Power / 144 7.5.8Anabolism: How Microbes Use Energy Trapped in High-Energy Bonds to Drive
Energy-Consuming Reactions / 145 7.5.9Carbon Assimilation by Mixotrophs, Photoheterotrophs, and Heterotrophs / 147
7.6Microbial Mineralization of Organic Matter / 147 7.7Microbial Products of Metabolism That Can Cause Geomicrobial Transformations / 149 7.8Physical Parameters That Inuence Geomicrobial Activity / 149 7.9Summary / 151 References / 151
acid (DNA). This structure is often called the bacterial chromosome, but unlike the chromosomes of eukaryotic cells, it does not contain structural protein such as histone, nor is it surrounded by a nuclear membrane. The molecular size of a prokaryotic chromosome measures on the order of 109 daltons (Da). Some genetic information in prokaryotes may also be located in one or more extrachromosomal circularized DNA molecules, called plasmids. The exact molecular size of different plasmids varies, depending on the amount of genetic information they carry, but generally ranges around 107 Da.
