Growth responses of a Cylindrotheca closterium strain from the Golden Horn Estuary to temperature, salinity and irradiance

The growth response of a diatom Cylindrotheca closterium strain (DEB132303) isolated from the Golden Horn Estuary (Sea of Marmara) was investigated under different environmental conditions. C. closterium cells were grown in a silica-enriched K-medium under various temperatures (11, 18, 25 and 32°C), salinities (6, 12, 18, 24, 30 and 36 psu) and irradiances (10, 20, 50 and 65 μmol photons m⁻² s⁻¹). By the end of the acclimatization period, no viable C. closterium cells were present at temperatures of 4°C and 32°C and salinities of 6 and 36 psu, which marked the upper and lower boundaries of its environmental tolerance. The maximum specific growth rates (µmax) were 1.45 d⁻¹ at temperature of 18°C (18 psu, 50 μmol photons m⁻² s⁻¹), 1.08 d⁻¹ at salinity of 24 psu ( 18°C, 50 μmol photons m⁻² s⁻¹) and 1.80 d⁻¹ at irradiance of 65 μmol photons m⁻² s⁻¹ (18°C, 18 psu), in temperature, salinity and light experiments, respectively. The maximum cell density (Dmax) was 5×10⁵ cells mL⁻¹ at temperature of 25°C, salinity of 18 psu and irradiance of 50 μmol photons m⁻² s⁻¹. Growth rate varied significantly among different temperature, salinity and irradiance treatments (ANOVA, p<0.001) and there was a positive correlation between growth rate and irradiance (r= 0.98, p<0.01). These results demonstrate that these environmental parameters affect significantly the growth of this C. closterium strain.