Cyclodextrin Glucanotransferase Activity of Microbial Strains Isolated from Yam-Cultivation Soils in Northwestern Benin

β-Cyclodextrin, an industrially important oligosaccharide, is produced by microbial enzymes such as cyclodextrin glucanotransferase (CGTase). This study investigated ways to optimize the enzymatic activity of CGTase from Bacillus cereus, Bacillus pumilus, Bacillus brevis, and Bacillus subtilis strains isolated from soils in north-western Benin. Cyclization activity of CGTase and the influence of pH, temperature, and metal ions were assessed using conventional assays, together with bioconversion kinetics and cyclodextrin yield. The results revealed several optimal conditions for enhancing β-cyclodextrin biosynthesis, with strong strain-and substrate-dependent variations. Bacillus pumilus, Bacillus brevis, and Bacillus subtilis showed stable activity irrespective of the substrate used, whereas Bacillus cereus proved more sensitive to the type of starch. Bacillus brevis remained active under acidic conditions (pH 5-6), whereas Bacillus cereus, Bacillus pumilus, and Bacillus subtilis showed optimal activity at neutral to alkaline pH (7-10). All CGTases were active between 37°C and 60°C but became inactive at 70°C. Magnesium stimulated enzymatic activity, while copper inhibited the enzyme at concentrations above 5 mM. β-cyclodextrin biosynthesis was detected after 8 hours of incubation, with higher yields obtained on potato starch. Peak β-cyclodextrin production was achieved with Bacillus brevis on potato starch (0.546±0.022 mM), versus 0.043±0.003 mM on soluble starch. For Bacillus cereus and Bacillus pumilus, potato starch also significantly increased β-Cyclodextrin yields (0.251±0.006 mM and 0.195±0.009 mM, respectively), whereas no significant substrate effect was observed for Bacillus subtilis. Optimizing β-cyclodextrin production therefore requires prior knowledge of the pH, temperature, substrate, and metal-ion conditions best suited to the selected strain for efficient CGTase production.