THE EFFECTS OF INCUBATION-TIME, TEMPERATURE, LIGHT, SALINITY, AND PHOSPHORUS ON GROWTH AND HEPATOTOXIN PRODUCTION BY NODULARIA STRAINS

The effects of incubation time, temperature, light, salinity, and phos phorus on growth and nodularin production by two strains of Nodularia spumigena cyanobacteria (BY1 and HEM) and one strain of Nodularia spha eroscarpa (HKVV) were studied in the laboratory. All strains were isol ated from cyanobacterial water blooms in the Baltic Sea. Hepatotoxic s trains BY1 and HEM produced toxin under all growth conditions, while t he strain HKVV was always non-toxic. The non-toxic HKVV strain grew po orer than the toxic ones under all conditions except at the lowest tem perature and lowest phosphorus concentration tested. The cells of stra in BY1 contained twice as much toxin as those of strain HEM. Highest t oxin concentrations within cells were detected after incubation of 12 to 15 days, and after that concentrations decreased. Toxin concentrati ons in growth media increased during incubation. Temperature had a sta tistically significant effect on growth and toxin levels in media. Gro wth and toxin production were highest at 20-degrees-C. Differences in irridance had no statistically significant effect on growth or toxin p roduction at light intensities tested. Statistically, salinity had a s ignificant effect on dry weights and toxin concentrations in media. To xin production and growth of strain BY 1 were highest at 5 parts per t housand salinity, while salinity had no effect on toxin production by strain HEM. Strains HEM and HKVV tolerated higher salinities than stra in BY1. Phosphorus had a significant effect on growth. Growth and toxi n production by both toxic strains were lowest at the phosphorus conce ntration of 0.3mgl-1 and highest at 0.6mgl-1 (test range 0.3-1.0mgl-1) These results indicate that nodularin production is influenced by env ironmental factors.