Optimization Of Growth Conditions Of Microcystis Aeruginosa Using Response Surface Methodology

According to the item named "China Lake Nutrient Criteria and Eutrophication Control Standard Research", the thesis took Microcystis aeruginosa as an example, and studied the relationship between 8 enviromental factors(including temperature, light intensity, pH, N, P, Fe, Mg and Ca) and cell growth using response surface methodology. Simultaneously the influence in different nitrogen forms (NO3--N and NH4+-N) was considered. This would be helpful for establishing reference conditions of lake nutrients.The main-effect factors were selected in accordance with two-level Plackett-Burman screening design. Four significant variables(NaNO3, K2HPO4, Fe·citrate·H2O, and temperature) were screened for optimized studies using NO3--N, in which temperature was the most significant factor with Etemperature= 3.9708. Higher concentration of K2HPO4 could inhibit the growth of microcystis aeruginosa, and other factors have positive effects to cell growth. When NH4+-N was used, cell growth was influenced by the factors with decreasing order of importance as temperature>light intensity>Fe·citrate·H2O>NH4Cl comparing the values of effects (Etemperature=2.7340,Elight int ensity=1.1465,EFe·citrate·H2O=0.9944, ENH4Cl=-0.8869), in which NH4Cl could inhibit Microcystis aeruginosa growth.After the main-effect factors were confirmed, three-level Box-Behnken design were used to optimize cell growth conditions. The results indicated that cell maximum biomass were influenced by main-effect factors individually in both NO3--N and NH4+-N. The interactions between main-effect factors were not as significant as their individual influences, but some of the interactions were relatively significant, such as interaction between NaNO3 and K2HPO4, and interaction between K2HPO4 and Fe-citrate-H2O using NO3--N; interaction between temperature and light intensity using NH4+-N. The results have also revealed that Microcystis aeruginosa was in optimum growth when the critical border values of the variables were determined as temperature 29℃, K2HPO4 0.057 mmol·L-1, NaNO3 1.059 mmol·L-1, Fe·citrate·H2O 0.024 mmol·L-1; similarly as NH4Cl 1.059 mmol·L-1, Fe·citrate·H2O 0.016 mmol·L-1, temperature 26℃, light intensity 71μmol·(m2·s)-1.3. The validated results of model indicated that the influences of environmental factors to growth of Microcystis aeruginosa were effectively and quickly revealed using statistical experimental design.