On the effect of abiotic environmental factors on production of bioactive oligopeptides in field populations of Planktothrix spp. (Cyanobacteria)

The variability in abundance of bioactive oligopeptides in Planktothrix spp. biomass in Lake Steinsfjorden, Norway, was examined for the period May 2003-August 2004, both temporally (over the year) and spatially (by depth). Of the 33 oligopeptides recorded, desmethyl-microcystin RR and LR, anabaenopeptin B, aeruginosin 583, oscillamide Y, oscillaginin B and oscillapeptin G were studied in detail. Of these desmethyl-microcystin RR had the highest average concentration (2.5 +/- 3.0 mu g L-1) and showed similar distributional patterns as the Planktothrix spp. biomass. Multivariate regression models, called generalized additive models (GAMs), were used to investigate the effect of temperature, irradiance, macronutrients, depth and date on the cellular oligopeptide content of Planktothrix spp. GAMs explained between 50 and 94% of the total variance in the abundance of oligopeptides per unit Planktothrix spp. biomass and also ranked parameters according to their contribution to this variance. Date was the most important contributor, linked to the waxing and waning of the four Planktothrix chemotypes found in Lake Steinsfjorden. There was an overall trend of increase in oligopeptide abundances per unit Planktothrix spp. biomass by depth. The factors affecting growth, temperature, irradiance and macronutrients had only a minor effect, explaining on average less than 10% of the variance included in the statistical models. The various classes of oligopeptides appeared to be influenced by environmental factors in a similar manner, suggesting that these oligopeptides may have a similar function in cyanobacteria.