Microbiology of Environmental Engineering Systems

Abstract

Type of energy generation is the major feature in physiological classification of prokaryotes. Chemotrophs can be separated within four groups by the type of electron acceptor: (a) anaerobic fermenting prokaryotes, producing biologically available energy by intramolecular oxidation-reduction; (b) anaerobically respiring prokaryotes, using other than oxygen electron acceptors; (c) microaerophilic bacteria, producing energy by aerobic respiration at low concentration of oxygen; (d) obligate aerobes, producing biologically available energy with oxygen as electron acceptor. There are also intermediary subgroups, which are using different types of energy production, depending on conditions. Phototrophs also can be classified into related physiological groups by the type of electron donor: (a) electron donors are products of anaerobic fermentation (organic acids, alcohols, and H2); (b) electron donors are products of anaerobic respiration (H2S, Fe2+); (c) electron donors are products of microaerophilic respiration (S); (d) electron donors are products of aerobic respiration (H2O). To overcome contradiction between the physiological groups and rRNA gene sequencing-based phylogenetic groups, the periodic table of prokaryotes comprising and explaining the existence of all physiological groups of prokaryotes was proposed. The main feature of the periodic table of prokaryotes is three parallel phylogenetic lines: (a) prokaryotes with Gram-negative type cell wall, habiting mainly in aquatic systems with stable osmotic pressure; (b) prokaryotes with Gram-positive type cell wall, habiting mainly in terrestrial systems with varied osmotic pressure; (c) Archaea that lack conventional peptidoglycan and habiting mainly in extreme environments. There are four periods in the periodic table of prokaryotes: anaerobic fermentation, anaerobic respiration, microaerophilic respiration, and aerobic respiration. Three phylogenetic lines and four periods create 12 groups comprising all chemotrophic and phototrophic prokaryotes. Existence of Gram-positive phototrophic bacteria using products of anaerobic, microaerophilic, and aerobic respiration as electron donors was predicted using this periodic table of prokaryotes. Evolutionary parallelism in phylogenetic lines of prokaryotes could be hypothetically explained by synchronous evolution of aquatic, terrestrial, and extreme ecosystems and horizontal exchange of genes between these ecosystems. The periodic table of prokaryotes helps to understand microbial physiological diversity of environmental engineering systems and can be used in the design of environmental engineering processes.