Effect of EDTA additions on natural Trichodesmium spp. (Cyanophyta) populations

Despite nearly two decades of intensive research, many questions regarding the physiology and ecology of the marine, non-heterocystous cyanobacterium, Trichodesmium, remain unresolved. We note here the effect of EDTA (ethylenediaminetetraacetate) on N₂ fixation by Trichodesmium, and the use of EDTA as a means of extending the viability of natural Trichodesmium spp. populations. We examined nitrogenase activity (NA) as a function of EDTA concentration, time of collection, light level, and iron addition. Samples collected early in the day and treated with EDTA maintain a steady rate of activity for hours longer than controls. Furthermore, samples preincubated through the night with EDTA were active the next morning, compared with controls that were inactive. The discovery that (10-50 μM) low concentrations of EDTA prolong the duration of NA of Trichodesmium during experimental manipulations without affecting the rate of acetylene reduction allows for longer term manipulative experiments to be conducted.