Green Nonsulfur Bacteria


Formerly known only as a group of gliding filamentous bacteria capable of anoxygenic photosynthesis, the green nonsulfur bacteria (phylum Chloroflexi) now are also known to comprise numerous chemotrophic bacteria of diverse ecophysiology and phylogeny. The most conspicuous representatives are the green‐ or orange‐coloured thermophilic bacteria which form dense microbial mats in hot springs. They are typical photoorganoheterotrophs and well adapted to their changing environment by their gliding motility, tactic responses and versatile physiology. Culture‐independent studies have revealed a plethora of novel, unknown 16S ribosomal ribonucleic acid (rRNA) gene sequence types, indicating that the diversity of these bacteria in the natural environment is only marginally understood. Nonphotosynthetic members of the Chloroflexi occur in freshwater, soil and decaying organic matter, as well as methanogenic granular sludge and other wastewater treatment systems where they seem to aid in granule formation and participate in carbohydrate turnover.

Keywords: Chloroflexi; anoxygenic photosynthesis; filamentous gliding bacteria; microbial mats; filamentous anoxygenic phototrophic bacteria

Figure 1.

(a, b) Overview of a typical hot spring habitat of phototrophic Chloroflexi located on the northern island of New Zealand. (c) Close up of orange‐coloured microbial mats of Chloroflexi. Bar, 10 cm. (d) Original site from which Roseiflexus castenholzii strain HLO8T was isolated. The red bacterial mat consisting of Roseiflexus castenholzii develops on a concrete wall in the outflow of Nakabusa hot spring (Nagano Prf., Japan). Dark green layers mainly consist of thermophilic cyanobacteria. Bar, 10 cm. (Photograph courtesy of Dr. Niels‐Ulrich Frigaard, University of Copenhagen.) (e) Straight and spiral multicellular filaments of Chloronema thriving in the chemocline of meromictic Mittlerer Buchensee (near Radolfzell, Southwestern Germany). Highly refractile inclusions in individual cells are accumulations of gas vesicles. The Chloronema filaments are accompanied by reddish cells of purple sulfur bacteria (Amoebobacter sp. and Lamprocystis sp.). Bar, 10 μm.

Figure 2.

Taxonomy and phylogenetic diversity of the phylum Chloroflexi. The taxonomic subdivisions are based on phylogenetic and chemotaxonomic considerations (compare Tables and ; Ribosomal Database Project II, 2008; Lee and Reichenbach, ; Hanada and Pierson, ) and include all recently and validly described strains. Numbers of not‐yet‐cultured and cultured phylotypes were obtained from RDP (Ribosomal Database Project II,



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Further Reading

Castenholz RW and Pierson BK (1995) Ecology of thermophilic anoxygenic phototrophs. In: Blankenship RE, Madigan MT and Bauer CE (eds) Anoxygenic Photosynthetic Bacteria, pp. 87–103. Dordrecht: Kluwer Academic Publishers.

Pierson BK and Castenholz RW (1974) A phototrophic gliding filamentous bacterium of hot springs, Chloroflexus aurantiacus, gen. and spec. nov. Archives of Microbiology 100: 5–24.

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How to Cite close
Overmann, Jörg(Sep 2008) Green Nonsulfur Bacteria. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0000457]