Characterization of Low-Temperature Enzymatic Reactions through Heterologous Expression and Functional Analysis of Two Beta-Glucosidases from the Termite Symbiotic Bacterium Elizabethkingia miricola Strain BM10

Lower termites need symbiotic microbes for cellulose digestion. Elizabethkingia miricola strain BM10 has been proposed as a symbiotic microbe that assists in low-temperature digestion and metabolism of Reticulitermes speratus KMT1, a termite on Bukhan Mountain, Seoul, Korea. In E. miricola strain BM10, β -glucosidase genes expressed at 10℃ were identified, and the psychrophilic enzymatic characteristic was confirmed by heterogeneously expressed proteins. Crude β -glucosidase in the culture broth of E. miricola strain BM10 showed specific enzymatic properties, and its substrate affinity was 4.69 times higher than that of Cellic CTec2. Among the genes proposed as β -glucosidase, two genes, bglB_1 and bglA_2 , whose gene expression was more than doubled at 10℃ than at 30℃, were identified. They were heterogeneously expressed in Escherichia coli and identified as psychrophilic enzymes with an optimal reaction temperature of about 20℃–25℃. In this study, E. miricola strain BM10, a symbiotic bacterium of lower termites, produced psychrophilic β -glucosidases that contribute to the spread of the low-temperature habitat of a lower termite, R. speratus KMT1.