Strain-level variability in growth and paralytic shellfish toxin content of Alexandrium catenella under different...

The growth and paralytic shellfish toxin (PST) contents of two Alexandrium catenella strains (CS-2412 and CS-2101) isolated from Jinhae-Masan Bay were examined under different combinations of temperature and salinity. The aim was to evaluate strain-specific physiological and toxicological responses under identical environmental conditions. Experiments were conducted in batch cultures with temperatures ranging from 15 to 30 °C and salinities from 15 to 35 psu. Both strains were completely inhibited at 30 °C at all salinity levels. Optimal growth occurred at 15-20 °C and 25-35 psu for both strains, but CS-2101 achieved a higher maximum growth rate and biomass than CS-2412. Toxin content patterns differed greatly between strains. CS-2412 exhibited a wide range of toxin contents (0.64-394 fmol cell^-1) and reached its maximum at 20 °C and 35 psu, where growth was low. CS-2101 maintained consistently lower toxin levels (16.5-94.2 fmol cell^-1), with the highest value at 15 °C and 30 psu, matching its optimal growth condition. These results demonstrate clear intra-species variability in growth and toxin responses to temperature and salinity. Such differences suggest that both genetic traits and nitrate utilization strategies may contribute to variability in PST synthesis. The findings highlight the importance of considering strain-level characteristics in ecological risk assessment and monitoring of harmful algal blooms.