Occurrence of facultative anoxygenic photosynthesis among filamentous and unicellular cyanobacteria

Abstract

Eleven [Oscillatoria spp., O. limnetica, O. salina, Lyngbya spp., Aphanotheca halophytica, Microcoleus sp. and Phormidium spp.] of 21 cyanobacteria strains examined are capable of facultative anoxygenic photosynthesis, as shown by their ability to photoassimilate CO2 in the presence of Na2S, 3-(3,4-dichlorophenyl)-1,1-dimethylurea and 703-nm light. These include different cyanobacterial types (filamentous and unicellular) of different growth histories (aerobic, anaerobic, marine and freshwater). O. limnetica, A. halophytica (7418), and Lyngbya (7104) have different optimal concentrations of Na2S permitting CO2 photoassimilation, above which the rate decreases: 3.5, 0.7, and 0.1 mM, respectively. In A. halophytica, for each CO2 molecule photoassimilated 2 sulfide molecules are oxidized to elemental S, which is excreted from the cells. The ecological and evolutionary significance of anoxygenic photosynthesis in the cyanobacteria is discussed.