Details for uncultured Chloroflexus sp.

Chloroflexis and most other green non-sulfur bacteria are filimentous prokaryotes that form thick microbial mats in neutral to alkaline hot springs. Although an anoxygenic phototroph, Chloroflexus is a "hybrid" phototroph in the sense that its photosynthetic mechanism shows features characteristic of both purple bacteria and green sulfur bacteria. Like the latter, Chloroflexus contains bacteriochlorophyll c and chlorosomes. However, the bacteriochlorophyll a located in the cytoplasmic membrane of cells of Chloroflexus is arranged to form a photosynthetic reaction center structurally similar to those of purple bacteria (by contrast, the reaction center of green sulfur bacteria is structurally quite different). It has thus been proposed that modern Chloroflexus may be a vestige of a very early form of phototroph that perhaps first evolved a photosynthetic reaction center and then received chlorosome-specific genes by lateral transfer.

Physiologically, Chloroflexus resembles purple nonsulfur bacteria in that photoautotrophy can be supported by (H₂S + CO₂) or (H₂ + CO₂). However, in Chloroflexus, phototrophic growth is best with organic compounds as carbon sources (photoheterotrophy). Chloroflexus also grows well in the dark as a chemoorganotroph by aerobic respiration. Interstingly, and this should be considered in light of the evolutionary position of Chloroflexus as the most phylogenetically ancient of anoxygenic phototrophs, autotrophy in Chloroflexus is based on a CO₂ incorporation pathway, the hydroxypropionate cycle, unique to this organism.