title: A GROWTH ADVANTAGE FOR MICROCYSTIN PRODUCTION BY MICROCYSTIS PCC7806 UNDER HIGH LIGHT(1).
abstract: Batch cultures of both Microcystis PCC7806 and a mcyA(-) knockout mutant (MT) of PCC7806 were cultured at three different light intensities and five media treatments, so as to vary cellular N:C ratios and concentrations and sampled daily over 5 d for analysis of microcystin concentration, cell numbers, and residual nitrate in the growth medium. A competitive survival advantage was noted at a high-light level (37 μmol photons · m(-2 ) · s(-1) ), where the toxic strain survived while the nontoxic strain became chlorotic. A strong correlation (r(2)  = 0.91, P < 0.001, N = 22) between microcystin concentration and growth rate was observed at high-light conditions. No advantage was observed at optimal or low-light conditions, and media composition had no significant effect on the relationship between toxicity and survival at high-light conditions. These data suggest a possible role for microcystin in protection against photooxidation.
authors.affiliation: Department of Biochemistry and Microbiology, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth, 6031, South Africa.
authors.forename: Richard R
authors.initials: RR
authors.lastname: Phelan
authors.affiliation: Department of Biochemistry and Microbiology, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth, 6031, South Africa.
authors.forename: Timothy G
authors.initials: TG
authors.lastname: Downing
keywords: Microcystis PCC7806; growth advantage; light; microcystin