Factors Controlling the Formation of Akinetes Adjacent to Heterocysts in the Cyanobacterium Cylindrospermum licheniforme Kutz.

Abstract

Summary: Substances which stimulate the formation of akinetes (spores) in Cylindrospermum licheniforme Kutz. are secreted into a phosphate-free sporulation medium by filaments of that cyanobacterium. One such substance, purified from the centrifugal supernatant fluid of sporulating cultures, initiated sporulation in a phosphate-containing culture medium. Certain amino acids, particularly tryptophan, and calcium glucuronate also strongly stimulated sporulation. Acetylene and ethylene were inhibitory. No significant effect of cyclic nucleotides was observed. The addition of 12.5 to 15 % (v/v) H2 stimulated sporulation in air or under CO2/O2/Ar (0.1:19.9:80, by vol.) by up to 2.5-fold, but did not significantly affect the reduction of acetylene by intact filaments. Thus, the stimulation of sporulation by hydrogen was not mediated by an effect on the fixation of nitrogen. Hydrogen uptake in a cell-free suspension derived from whole filaments was detected manometrically, with phenazine methosulphate as electron acceptor, at a rate of 5.8 μmol H2 (mg chlorophyll a)−1 h−1. The uptake hydrogenase activity derived from isolated heterocysts accounted for 84 × 2 % of the uptake hydrogenase activity from whole filaments, whereas no activity was detected in a fraction derived from the vegetative cells. The formation of the pattern consisting of spores contiguous with heterocysts may be controlled by either, or a combination of, (i) a sporulation-stimulatory substance, if that substance is synthesized solely in heterocysts, or (ii) some substance the concentration of which may be controlled by hydrogen assimilated by heterocysts.