NITROGEN-FIXATION BY THE BENTHIC FRESH-WATER CYANOBACTERIUM LYNGBYA-WOLLEI

The ability of the benthic cyanobacterium Lyngbya wollei to fix nitrogen was studied using field samples and axenic cultures. L. wollei was collected and isolated from Lake Okeechobee, Florida, where it forms extensive mats. Rates of acetylene reduction up to 39.1 nmol mg dry wt-1 h-1 were observed for field samples. The maximum observed rate of acetylene reduction in axenic laboratory cultures was 200 nmol mg dry wt-1 h-1. Aerobic conditions limited nitrogen fixation activity, but dark/light cycles promoted the development of activity. Reduced oxygen levels appeared to be required for the development of significant levels of nitrogenase activity. The level of irradiance also had a significant impact on the level of activity. The potential significance of nitrogen fixation to Lyngbya production is discussed.