Optimization of culture conditions of <italic>Isochrysis galbana</italic> by response surface method

Abstract

<italic>Isochrysis galbana</italic> has the advantages of small size and fast reproduction. It has become one of the main micro-algae with great potential for green sewage treatment technology under the new concept. Because of its high nutritional value, it is often used as bait in the artificial breeding of bivalve shellfish such as <italic>Meretrix meretrix</italic>, <italic>Solen grandis</italic>, <italic>Sinonovacula constricta</italic> and so on. Response surface method is a combination of statistics and mathematics. It not only has the interaction in the orthogonal experiment, but also can use the mathematical model to get the functional relationship between the response and each variable, so it is an effective method to further predict the combination of all variable factors and get the optimal response surface value to solve scientific and production problems. Specific growth rate refers to the increased biomass of single-celled organisms per unit mass per unit time, which is an important parameter reflecting the growth rate of single-celled organisms such as microalgae and bacteria. The specific growth rate can not only accurately reflect the specific growth rate of microalgae in a certain time period, but also can comprehensively reflect the dynamic changes of the balance between microalgae growth and mortality. In order to optimize the culture conditions of <italic>Isochrysis galbana</italic>, using the method of experimental ecology and response surface (Box-Behnken mode), different experimental groups with different temperatures, salinities and initial inoculation levels were set up. Single factor experiment and multifactor experiment (Box-Benhnken model) were constructed to obtain the specific growth rate of <italic>Isochrysis galbana</italic>. Results showed that: 1) In a certain range of temperature, salinity and initial inoculation level, the specific growth rate of <italic>Isochrysis galbana</italic> increased first and then decreased with the increase of various factors; 2) The optimization of culture conditions of <italic>Isochrysis galbana</italic> respectively were: temperature 26.38 ℃, salinity 26.61, and initial inoculation level 1.29×10⁶ cell·mL^-1,and the maximum specific growth rate of <italic>Isochrysis galbana</italic> was 0.44 d^-1. The model conclusion data is available and can be applied to the actual production process.Our results could provide scientific basis for laboratory culture and large-scale propagation of <italic>Isochrysis galbana</italic>.In this paper, taking the specific growth rate of <italic>Isochrysis galbana</italic> as an index, the optimum conditions of suitable temperature, salinity and initial inoculation level were optimized by response surface method to provide scientific basis for laboratory culture and large-scale breeding of <italic>Isochrysis galbana</italic>.