Research progress in productions of gellan gum by fermentation of microorganism

Gellan is used in the food, pharmaceutical and industries and produced by Sphingomonas paucimobilis. Fermentation is the optimal production of gellan gum.The gellan biosynthetic pathway consists of three sequential steps:intracellular synthesis of sugar-activated precursors, assembly of the tetrasaccharide repeat units linked to the inner membrane, and translocation of the repeat united to the periplasmic space followed by their polymerization and export through the outer membrane.Some enzymes, such as UDP-glucose pyrophosphorylase (UGP) , TDP-glucose pyrophosphorylase (TGP) and UDP-glucose dehydrogenase (UGD) , are critical for gellan gum biosynthesis.Strains used for gellan gum production could be acquired by mutagenesis, gene recombining and gene knockout.Some new technologies, such as the optimal carbon and nitrogen sources and C/N, the optimal fermentation temperature and dissolved oxygen control, the fermentation kinetics model and response surface experimental design methods, were being used in gellan gum production gradually.In this paper, the research progress related to biosynthesis pathway of gellan and biosynthetic enzymes in microorganisms were reviewed, and the latest research of gellan producing strains was summarized. At last, we concluded an outlook for research directions in building gellan genetically engineered strains.