Effects of organic chemicals on growth of Methylosinus trichosporium OB3b

Effects of organic chemicals on the growth rate and cell density of Methylosinus trichosporium OB3b, a type II methanotroph, were studied. The examined organic chemicals were vitamins, amino acids and organic acids, including folic acid, riboflavin, tetrahydrofuran, cysteine, tyrosine, glycine, pyruvic acid, malate, maleic acid, and citrate. The results showed that M. trichosporium OB3b could not utilize the added organics as the sole carbon source for cell growth without the presence of methane. Riboflavin and organic acids such as malate, citrate, succinate and maleate could obviously improve the cell concentration of this strain. Among them, citrate exhibited the most significant effect on cell growth enhancement. When citrate was added at an optimal concentration of 0.015 mmol/L, the maximal cell concentration could reach 0.75 g dry cell weight/L, about 3.5 times that of the control without citrate addition. Furthermore, the improvement of the cell growth of M. trichosporium OB3b by the addition of citrate was confirmed in a bioreactor with a continuous supply of air and methane.