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Cyclodextrin glycosyltransferase (CGTase) is a significant extracellular enzyme with diverse functions. CGTase is widely used in production of cyclic α-(1,4)-linked oligosaccharides (cyclodextrins) from starch via transglycosylation reaction. Recent discoveries of novel CGTases from different microorganisms have expanded its applications but natural CGTase have lower yield, leading to heterologous expression for increased production to meet various needs. Moreover, significant advancements in directed evolution approach have been explored to alter the molecular structure of CGTase to enhance its performance. This review comprehensively summarizes the strategies employed in heterologous expression to boost CGTase production and secretion in various host. It also outlines molecular engineering approaches aimed to improving CGTase properties, including product and substrate specificity, catalytic efficiency, and thermal stability. Additionally, a considerable stability against changes in temperature and organic solvents can be obtained by immobilization.

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Cyclodextrin glucanotransferase (CGTase) is an extracellular enzyme of the GH13 α-amylase family that catalyzes a unique intramolecular reaction known as cyclization to transform α-1, 4-glucans and similar starches into cyclodextrins. They also catalyze intermolecular transglycosylation reactions namely coupling, disproportionation, and some hydrolyzing effects on starch. The monomeric structures of the CGTase exhibit five domains (A, B, C, D, and E domains) with different molecular weights and amino acid sequences depending on the source. Among bacteria, Bacillus genus covers approximately 90% of the CGTase producers, while other genera like Klebsiella, Paenibacillus, and Thermoanaerobacter also shown decent contributions in recent studies. CGTase production is highly supported by alkaliphilic bacteria under submerged fermentation rather than solid-state fermentation. The bacterial sources, biochemical properties, production conditions, and structure of CGTases are compiled in this review. Cyclodextrins have the unique property of making inclusion complexes with various compounds, hence widely used in the food, pharmaceutical, cosmetics, laundry, and chemical sectors. This review presents a comprehensive view of CGTase produced by Bacillus spp., and other bacterial genera like Klebsiella, Paenibacillus, and Microbacterium. It also gives insight of the properties and recent biotechnological applications of cyclodextrins. KEY POINTS: • Transglycosylation reactions catalyzed by CGTase and their structural properties. • Comparative data of CGTase production by various genera and Bacillus spp. • Structures, properties, and applications of different cyclodextrins.

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Microbial surfactants are amphiphilic surface-active substances aid to reduce surface and interfacial tensions by accumulating between two fluid phases. They can be generically classified as low or high molecular weight biosurfactants based on their molecular weight, whilst overall chemical makeup determines whether they are neutral or anionic molecules. They demonstrate a variety of fundamental characteristics, including the lowering of surface tension, emulsification, adsorption, micelle formation, etc. Microbial genera like Bacillus spp., Pseudomonas spp., Candida spp., and Pseudozyma spp. are studied extensively for their production. The type of biosurfactant produced is reliant on the substrate utilized and the pathway pursued by the generating microorganisms. Some advantages of biosurfactants over synthetic surfactants comprise biodegradability, low toxicity, bioavailability, specificity of action, structural diversity, and effectiveness in harsh environments. Biosurfactants are physiologically crucial molecules for producing microorganisms which help the cells to grasp substrates in adverse conditions and also have antimicrobial, anti-adhesive, and antioxidant properties. Biosurfactants are in high demand as a potential product in industries like petroleum, cosmetics, detergents, agriculture, medicine, and food due to their beneficial properties. Biosurfactants are the significant natural biodegradable substances employed to replace the chemical surfactants on a global scale in order to make a cleaner and more sustainable environment.

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Biosurfactant production by Pseudomonas guguanensis D30 was reported using mineral oil in submerged condition. Twelve medium components were tested at two levels by Plackett-Burman design, among them, mineral oil, yeast extract, peptone, MgSO4, and CaCl2 found significant on the basis of emulsification index. These five significant components were further optimized through central composite design (CCD). The experimental design was successfully used for regression analysis and the significant model suggested the solution of 10% (v/v) mineral oil, 3.0 g/L (w/v) yeast extract and 0.2 g/L (w/v) peptone for 13.14 g/L predicted biosurfactant production. We kept the suggested concentrations of medium components and got 13.34 ± 0.08 g/L biosurfactant production, which is almost double the conventional one-factor-at-a-time production (7.126 ± 0.12 g/L). It reduced the surface tension of the medium up to 28 ± 1.2 mN/m. We found ethyl acetate a suitable solvent for biosurfactant extraction amongst methanol, chloroform, and methanol:chloroform. The partially purified biosurfactant was chemically characterized as lipopeptide by Fourier transform infrared spectroscopy (FT-IR).

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