The correlations of fermentation metabolites with sporulation capability and varieties of Rhizopus arrhizus

Abstract:

[Objective] In order to provide guidance for industrial production, this study investigated the diversity and correlation of metabolites among Rhizopus arrhizus strains in different ecological habitats, in different geographical locations, with different sporulation capacities, and of different taxonomic varieties.[Methods] Sixty-eight representative strains of R. arrhizus were inoculated in glutinous rice media for liquid fermentation, and the yields of secondary metabolites were determined by high-performance liquid chromatography. Pearson correlation coefficients between fermentation products were calculated. The correlation between strains and fermentation characteristics was assessed by multivariate analysis of variance and principal component analysis.[Results] A total of seven fermentation products were detected, including glucose (average yield in percentage:70.96%), ethanol (17.87%), lactic acid (6.63%), maltose (1.80%), malic acid (1.46%), fumaric acid (0.92%), and glycerin (0.36%). Maltose was metabolized independently, while the other six were divided into two groups with a negative inter-group correlation. The first group contained glucose, lactic acid, and glycerol, which were positively correlated with each other. The second group included ethanol, malic acid, and fumaric acid, also showing positive correlations. Fermentation characteristics were significantly correlated with sporulation capacities and taxonomic varieties, while slightly with ecological habitats and geographical locations. The strains not producing spores in synthetic mucor liquid medium had significantly stronger fermentation ability of than the SM spore-producing strains. In particular, strain XY01957 had the potential for industrial production since it could produce glucose at a yield as much as 138.30 g/L. The varieties arrhizus and tonkinensis had lower content of fumaric acid and malic acid while higher content of lactic acid and glycerin, whereas delemar was obviously opposite to the two varieties above with respect to all these components.[Conclusion] This study demonstrated high correlations among fermentation metabolites, sporulation capacities, and taxonomic varieties of R. arrhizus, laying a sound foundation for population genetic research. Some high-quality strains were screened out, providing solid support for the fermentation industry.