Effects of different inoculation densities on growth and toxin production ofAlexandrium minutum

Effects of different inoculation densities on growth and toxin production of Alexandrium minutum were studied.Experiments were conducted under conditions of varying inoculation densities(0.05×10⁴,0.10×10⁴,0.15×10⁴,0.30×10⁴cells/mL).Higher inoculation densities always resulted in shorter lag phase of A.minutum,and an earlier setting in of the steady growth phase.However,the specific growth rate and maximum cell concentration of A.minutum decreased with increasing inoculation densities.The multiplication models developed correlated well with the observations,as the inoculation density increased,the initial-density dependent parameter a also deceased and the reduction of environmental capacity,instantaneous multiplication included.According to MBA analysis,toxicity of A.minutum is typically highest when cells are growing fast in early exponential phase and lowest as growth slows and eventually stops in plateau phase.The PSP-toxin congeners,GTX1(2.14 fmol/cell),GTX2(2.08 fmol/cell),GTX3(4.97 fmol/cell),GTX4(5.04 fmol/cell)were analysed by high-performance liquid chromatography with fluorescence diction(HPLC-FLD).Result of this study implied that toxin production of the dinoflagellate A.minutum is better in 0.10×10⁴-0.15×10⁴ cells/mL than other condition of inoculations densities.