Summary: Four strains of the thermophilic phototrophic green bacterium Chloroflexus aurantiacus were tested for nitrogenase activity under a variety of nutritional conditions consistent with nitrogenase derepression in anoxygenic photosynthetic bacteria. Although all strains of C. aurantiacus could grow with various amino acids as sole nitrogen sources, no growth on N2 was observed; acetylene reduction was undetectable in cells grown under any nutritional conditions. The inability of Chloroflexus to fix N2 is discussed in connection with its thermophilic character.
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Heda et al. (1986) studied this question.