Biophysicochemical Characterization of an Alkaline Protease from Beauveria sp. MTCC 5184 with Multiple Applications

Biochemical characterization of a semi-purified aspartic protease from sea catfish Bagre panamensis with milk-clotting activity

Pepsin from stomach of Bagre panamensis was semi-purified and biochemically characterized. The acid proteolytic activity and purification fold were 3875 U/mg protein and 91.85, respectively, after purification process. The optimum pH and temperature for semi-purified protease were 2-3 and 65 °C, respectively. The enzyme activity was stable after heating proteases at 50 °C for 120 min, but only 30% residual activity was detected after heating at 65 °C for 30 min. SDS-PAGE analysis showed two proteins bands after dialysis (26.1 and 38.6 kDa). Only the band of 38.6 kDa had proteolytic activity, which was inhibited using pepstatin A. Organic solvents, surfactants and reducing agents affect the proteolytic activity at different extent; however, metal ions or EDTA have no impact on protease activity. The semi-purified protease exhibited milk coagulant activity, with a maximum activity at 45 °C. The obtained results highlight the potential biotechnological use of B. panamensis pepsin.

The Beauveria bassiana Gas3 β-Glucanosyltransferase Contributes to Fungal Adaptation to Extreme Alkaline Conditions

Fungal β-1,3-glucanosyltransferases are cell wall-remodeling enzymes implicated in stress response, cell wall integrity, and virulence, with most fungal genomes containing multiple members. The insect-pathogenic fungus Beauveria bassiana displays robust growth over a wide pH range (pH 4 to 10). A random insertion mutant library screening for increased sensitivity to alkaline (pH 10) growth conditions resulted in the identification and mapping of a mutant to a β-1,3-glucanosyltransferase gene (Bbgas3). Bbgas3 expression was pH dependent and regulated by the PacC transcription factor, which activates genes in response to neutral/alkaline growth conditions. Targeted gene knockout of Bbgas3 resulted in reduced growth under alkaline conditions, with only minor effects of increased sensitivity to cell wall stress (Congo red and calcofluor white) and no significant effects on fungal sensitivity to oxidative or osmotic stress. The cell walls of ΔBbgas3 aerial conidia were thinner than those of the wild-type and complemented strains in response to alkaline conditions, and β-1,3-glucan antibody and lectin staining revealed alterations in cell surface carbohydrate epitopes. The ΔBbgas3 mutant displayed alterations in cell wall chitin and carbohydrate content in response to alkaline pH. Insect bioassays revealed impaired virulence for the ΔBbgas3 mutant depending upon the pH of the media on which the conidia were grown and harvested. Unexpectedly, a decreased median lethal time to kill (LT50, i.e., increased virulence) was seen for the mutant using intrahemocoel injection assays using conidia grown at acidic pH (5.6). These data show that BbGas3 acts as a pH-responsive cell wall-remodeling enzyme involved in resistance to extreme pH (>9).IMPORTANCE Little is known about adaptations required for growth at high (>9) pH. Here, we show that a specific fungal membrane-remodeling β-1,3-glucanosyltransferase gene (Bbgas3) regulated by the pH-responsive PacC transcription factor forms a critical aspect of the ability of the insect-pathogenic fungus Beauveria bassiana to grow at extreme pH. The loss of Bbgas3 resulted in a unique decreased ability to grow at high pH, with little to no effects seen with respect to other stress conditions, i.e., cell wall integrity and osmotic and oxidative stress. However, pH-dependent alternations in cell wall properties and virulence were noted for the ΔBbgas3 mutant. These data provide a mechanistic insight into the importance of the specific cell wall structure required to stabilize the cell at high pH and link it to the PacC/Pal/Rim pH-sensing and regulatory system.

Response surface methodology for production, characterization and application of solvent, salt and alkali-tolerant alkaline protease from isolated fungal strain Aspergillus niger WA 2017

Isolated strain Aspergillus niger WA 2017 was selected as potential protease producer and was identified on the basis of 18S rDNA gene homology. Optimization of protease production conditions was performed using statistical methodology. The most significant factors were identified by Plackett-Burman design (PB) and were optimized by Central Composite design (CCD). The enzyme production was increased by 3.6-fold with statistically optimized medium when compared to the basal medium. Based on the protease activity, 25-50% ethanol fraction exhibited the highest specific activity. The partially purified enzyme showed its highest activity (4.7-fold) after 10 min incubation at pH 10.0 and 60 °C. The enzyme was stable over a wide range of pH (7-11) and salt concentration (up to 20%). Kinetic parameters Michaelis constant (K_m) and maximum velocity (V_max) were calculated at varying casein concentrations. Additionally, thermal stability of the enzyme was substantially improved by NaCl. The enzyme showed excellent stability and compatibility in presence of organic solvents and detergents retaining 115.3 and 114.5% of its activity in presence of ethanol and Tide, respectively at 40 °C for 1 h. The results revealed that the produced enzyme was able to recover silver from used X-ray film under optimized condition using statistical methodology (CCD).

Charge-switchable gold nanoparticles for enhanced enzymatic thermostability

Zwitterionic amino acids allow the synthesis of charge-switchable metal nanoparticles, which support efficient immobilization of enzymes on nanoparticles, leading to high thermal stability and enzymatic efficiency.