Effect of an inorganic nitrogen source (NH4)2SO4 on the production of welan gum from Sphingomonas sp. mutant obtained through UV-ARTP compound mutagenesis

Abstract

As one of the most expensive extracellular polysaccharides, welan gum is widely used in biomedicine, food products, and petroleum because of its unique structure and excellent rheological properties. To reduce the cost of welan gum fermentation, together with (NH4)2SO4, which served as the sole nitrogen source, a high-welan-gum-producing mutant, B-8, screened through UV-ARTP compound mutagenesis was used. Under optimum conditions (C:N ratio 25:1, sucrose 50 g/L, (NH4)2SO4 4 g/L, and adding 8 mM NaCl at 32 h fermentation), the yield of welan gum and sucrose conversion were 18.86 g/L and 0.38 g/g, respectively, which were 98.95% and 137.50% higher than those achieved with the parent strain FM01, respectively. After the same treatment process, IN-welan (obtained with (NH4)2SO4) consumed less 95% ethanol, had higher molecular weight, and exhibited better rheological properties than ON-welan (obtained with beef extract). Transcriptome analysis revealed that (NH4)2SO4 could affect the synthetic pathway and monosaccharide content of welan gum by increasing bacterial chemotaxis and the availability of key intermediates. The fermentation performance of Sphingomonas sp. mutants could further be improved by providing several target genes to the mutants through metabolic engineering.