Biosynthesis and physicochemical properties of low molecular weight gellan produced by a high-yield mutant of Sphingomonas paucimobilis ATCC 31461.

Gellan gum (GG) is used in many industries. Here, we obtained a low molecular weight GG (L-GG) directly produced by M155, the high-yield mutant strain of Sphingomonas paucimobilis ATCC 31461, which was selected using UV-ARTP combined mutagenesis. The molecular weight of L-GG was 44.6 % lesser than that of the initial GG (I-GG), and the GG yield increased by 24 %. The monosaccharide composition and Fourier transform-infrared spectroscopic patterns of L-GG were similar to those of I-GG, which indicated that the decrease in the molecular weight of L-GG was probably because of reduction in the degree of polymerization. In addition, microstructural analysis revealed that the surface of L-GG was rougher, with smaller pores and tighter network, than that of I-GG. L-GG showed low hardness, gumminess, and chewiness, which are indicative of better taste. The results of rheological analysis revealed that the L-GG solution is a typical non-Newtonian fluid with low viscoelasticity, which exhibited stable dynamic viscoelasticity within 20-65 °C. To the best of our knowledge, this is the first report of direct biosynthesis of low molecular weight GG during fermentation, which will reduce the manufacturing costs. Our observations provide a reference for precise and expanded applications of GG.

Rapid Screening of High-Yield Gellan Gum Mutants of Sphingomonas paucimobilis ATCC 31461 by Combining Atmospheric and Room Temperature Plasma Mutation with Near-Infrared Spectroscopy Monitoring.

In this study, an efficient mutagenesis and rapid screening method of high-yield gellan gum mutant by atmospheric and room temperature plasma (ARTP) treatment combined with Near-Infrared Spectroscopy (NIRS) was proposed. A NIRS model for the on-line detection of gellan gum yield was constructed by joint interval partial least squares (siPLS) regression on the basis of chemical determination and NIRS acquisition of gellan gum yield. Five genetically stable mutant strains were screened using the on-line NIRS detection of gellan gum yield in the fermentation from approximately 600 mutant strains induced by ARTP. Remarkably, compared with the original strain, the gellan gum yield of mutant strain 519 was 9.427 g/L (increased by 133.5%) under the optimal fermentation conditions, which was determined by single-factor and response surface optimization. Therefore, the method of ARTP mutation combined with the NIRS model can be used to screen high-yield mutant strains of gellan gum and other high-yield polysaccharide strains.

Effect of ultrasonication on the metabolome and transcriptome profile changes in the fermentation of Ganoderma lucidum.

Development of an efficient liquid fermentation method is helpful for food and pharmaceutical applications. This study investigated the effect of ultrasonication on the liquid fermentation of Ganoderma lucidum, a popular edible and medical fungi. Significant changes at both metabolic and transcriptional levels in mycelia were induced by ultrasound treatment. Compared with the control, 857 differential metabolites were identified (578 up- and 279 down-regulated metabolites), with more metabolites biosynthesis after sonication; 569 differentially expressed genes (DEGs) (267 up- and 302 down-) and 932 DEGs (378 up- and 554 down-) were identified in ultrasound-treated samples with recovery time of 0.5 and 3 h, respectively. Furthermore, 334 DEGs were continuously induced within the recovery time of 3 h, indicating the lasting influence of sonication on mycelia. The DEGs and differential metabolites were mainly involved in pathways of carbohydrate, energy metabolism, amino acids, terpenoids biosynthesis and metabolism and membrane transport, suggesting that ultrasound induced multifaceted effects on primary and secondary metabolism. Ultrasonication enhanced the triterpenoids production of G. lucidum (34.96 %) by up-regulating the expression of terpenoids synthase genes. This study shows that the application of ultrasound in liquid fermentation of G. lucidum is an efficient approach to produce more metabolites.