Effects of Different Types and Concentrations of Organic Carbon Sources on the Growth and Biochemical Composition of Nostoc sphaeroides

Organic carbon sources are essential nutrients for the growth and development of autotrophic microorganisms. To investigate the effects of different organic carbon sources on Nostoc sphaeroides, a 9-day cultivation experiment was conducted using four types of organic carbon sources (glucose, sucrose, sodium pyruvate, and sodium acetate) each at four concentrations (0.01, 0.1, 0.2, and 0.4 mol·L^-1). After the experiment, the relative growth rate (RGR) and the contents of four biochemical compositions (chlorophyll a, soluble sugars, soluble proteins, and phycocyanin) of N. sphaeroides were measured. The results showed that both the types and concentrations of organic carbon sources had significant influences on the growth and biochemical compositions of N. sphaeroides. Glucose and sucrose significantly promoted the growth of N. sphaeroides, with the highest RGR observed at a sucrose concentration of 0.2 mol·L^-1. The addition of glucose and sucrose also stimulated the accumulation of soluble sugar, and the contents increased with the increasing carbon source concentration. As sucrose concentration enhanced, the chlorophyll a content of N. sphaeroides initially rose and then declined, reaching its peak at 0.2 mol·L^-1. In contrast, high concentrations of sodium pyruvate and sodium acetate inhibited the growth of N. sphaeroides. Additionally, the highest content of soluble proteins was observed at 0.1 mol·L^-1 of sodium pyruvate while the highest phycocyanin content was detected at 0.2 mol·L^-1 of sodium acetate. These findings provided effective strategies and data for the appropriate organic carbon source supplementation of the artificial cultivation of N. sphaeroides.