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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.

A natural bacterial isolate that shows multiple plant growth-promoting activities was isolated from fermented panchagavya (a mixture of five indigenous cow products). It is a gram-positive, endospore-forming bacteria identified as Bacillus sp. PG-8 by 16S rRNA gene sequencing. The Bacillus sp. PG-8 have shown multiple plant growth-promoting activities as indole acetic acid (2.78 μg/ml), gibberellic acid (0.7 mg/ml), ammonia (6.51 μmol/ml), exopolysaccharide (2.6% w/v) production, and phosphate solubilization (198.27 μg/ml). The Bacillus sp. PG-8 has ability to survive under the abiotic stress conditions such as temperature (28–46°C), pH (5.0–12.0), salt (0.5–20.0% w/v NaCl), and osmotic resistance (1–10% w/v PEG-6000). Due to its diverse characteristics, the effect of Bacillus sp. PG-8 was tested on Arachis hypogea (groundnut). The seeds treated with Bacillus sp. PG-8 demonstrated a 70% germination rate with seedling vigor indexes of 154. In pot study, Arachis hypogea growth showed 1.38, 1.38, 1.32, 1.39, and 1.52 times increase in root hair number, leaf numbers, leaf width, leaf length, and leaf area, respectively. The addition of Bacillus sp. PG-8 culture to the Arachis hypogea plant resulted in a significant improvement in plant growth. Bacillus sp. PG-8 is a spore producer with stress tolerance and multiple plant growth-promoting properties, which makes it a potential liquid biofertilizer candidate.

Cyclodextrin glucanotransferase (CGTase, EC 2.4.1.19) production using new alkaliphile Microbacterium terrae KNR 9 was investigated by submerged fermentation. Statistical screening for components belonging to different categories, namely, soluble and raw starches as carbon sources, complex organic and inorganic nitrogen sources, minerals, a buffering agent, and a surfactant, has been carried out for CGTase production using Plackett-Burman factorial design. To screen out k (19), number of variables, k + 1 (20), number of experiments, were performed. Among the fourteen components screened, four components, namely, soluble starch, corn flour, yeast extract, and K2HPO4, were identified as significant with reference to their concentration effect and corresponding p value. Although soluble starch showed highest significance, comparable significance was also observed with corn flour and hence it was selected as a sole carbon source along with yeast extract and K2HPO4 for further media optimization studies. Using screened components, CGTase production was increased to 45% and 87% at shake flask level and laboratory scale fermenter, respectively, as compared to basal media.

Cyclodextrin glucanotransferase (CGTase, EC. 2.1.1.19) produced using new alkaliphile Microbacterium terrae KNR 9 has been purified to homogeneity in a single step by the starch adsorption method. The specific activity of the purified CGTase was 45 U/mg compared to crude 0.9 U/mg. This resulted in a 50-fold purification of the enzyme with 33 % yield. The molecular weight of the purified enzyme was found to be 27.72 kDa as determined by SDS-PAGE. Non-denaturing gel electrophoresis and activity staining confirmed the presence of CGTase in crude and the ammonium sulfate precipitate fraction. The purified CGTase has a pI value of 4.2. The optimum pH of 6.0 and 60 °C temperature were found to be the best for CGTase activity. Purified CGTase showed 5.18 kcal/mol activation energy (Ea). The CGTase activity was increased in the presence of metal ions (5 mM): Ca+2 (130 %), Mg+2 (123 %), Mn+2 (119 %) and Co+2 (116 %). The enzyme activity was strongly inhibited in the presence of Hg+2 (0.0 %), Cu+2 (0.0 %) and Fe+2 (3.8 %). Inhibitor N-bromosuccinimide (5 mM) showed the highest 96 % inhibition of CGTase activity. SDS and triton X-100 among different detergents and surfactants (1.0 %, w/v) tested showed 92 % inhibition. Among the organic solvents checked for their effect on enzyme activity, 5 % (v/v) toluene resulted in 48 % increased activity. Polyethylene glycol-6000 showed a 26 % increase in the CGTase activity. The kinetic parameters K m and V max were 10 mg/ml and 146 µmol/mg min, respectively, for purified CGTase.