“Anoxygenic photot rophs are a widespread and metabolically diverse group of photosynthetic organisms which … anaerobic conditions for photosynthetic growth and development because synthesis of their pigments (bacteriochlorophylls and carotenoids ) (van Niel 1944; Pfennig and Truper 1977; Pfennig 1978), is strongly repressed by molecular oxygen (Cohen-Bazire et al. 1957).”