Two cyanobacteria isolated from marine microbial mats metabolized endogenous carbon reserves anaerobically in the dark. Microcoleus chthonoplastes reduced elemental sulfur to sulfide and Oscillatoria sp. additionally produced lactate in the absence of elemental sulfur. Under nitrogen fixing conditions, however, no sulfur reduction occurs. Lactate fermentation appeared to be the mechanism of anaerobic carbon degradation under these conditions. With a nitrogenase-reducible substrate, e.g. acetylene, added, lactate fermentation as well as sulfur reduction stops in cultures of Oscillatoria containing nitrogenase. In this case only ethylene production was observed. These cyanobacteria seem to possess the capability to carry out anaerobic dark metabolism... |