Taxonomy, Phylogeny, and General Ecology of Anoxygenic Phototrophic Bacteria

Abstract

Phototrophic bacteria, including oxygenic and anoxygenic phototrophic bacteria, can transform light energy into metabolically useful chemical energy by chlorophyll- or bacteriochlorophyll-mediated processes. Major differences between oxygenic and anoxygenic phototrophic bacteria relate to their photosynthetic pigments and the structure and complexity of the photosynthetic apparatus (Stanier et al., 1981). Photosynthesis in anoxygenic phototrophic bacteria depends on oxygen-deficient conditions, because synthesis of the photosynthetic pigments is repressed by oxygen (bacteria like Erythrobacter longus are exceptions to this rule); in contrast to photosynthesis in plants and cyanobacteria (including Prochloron and related forms), oxygen is not produced. Unlike the cyanobacteria and eukaryotic algae, anoxygenic phototrophic bacteria are unable to use water as an electron donor. Most characteristically, sulfide and other reduced sulfur compounds, but also hydrogen and a number of small organic molecules, are used as photosynthetic electron donors. [Anoxygenic photosynthesis with sulfide, an inhibitor of photosystem II, as electron donor is also carried out by some cyanobacteria using photosystem I only (Cohen et al., 1975; Garlick et al., 1977).] As a consequence, the ecological niches of anoxygenic phototrophic bacteria are anoxic parts of waters and sediments, which receive light of sufficient quantity and quality to allow phototrophic development. Representatives of this group are widely distributed in nature and found in freshwater, marine, and hypersaline environments, hot springs, and arctic lakes, as well as elsewhere. They live in all kinds of stagnant water bodies, in lakes, waste water ponds, coastal lagoons, stratified lakes, and other aquatic habitats, but also in marine coastal sediments, in moist soils, and in paddy fields.