Enhanced secretion and low temperature stabilization of a hyperthermostable and Ca2+‐independent α‐amylase of Geobacillus thermoleovorans by surfactants

Aims: Selection of suitable surfactants for enhancing and stabilizing α‐amylase of Geobacillus thermoleovorans. Methods and Results: Geobacillus thermoleovorans was cultivated in shake flasks containing 50 ml of starch‐yeast extract‐tryptone (SYT) medium with/without surfactants. Titres of the enzyme in media were monitored. The enzyme was also preserved at 4°C with/without surfactants and enzyme activities were determined. Among polyethylene glycol (PEGs) of different molecular weights, PEG 8000 (0·5%, w/v) caused a slight increase in the enzyme titre, while Tween‐20, Tween‐40 and Tween‐60 (0·03%, w/v) exerted a significant stimulatory effect on enzyme secretion. In the presence of SDS, Tween‐80 and cholic acid (0·03%, w/v), the enzyme production was nearly twofold higher than that in the control. The anionic (SDS, cholic acid) and non‐ionic (Tweens) detergents increased the cell membrane permeability, and thus, enhanced α‐amylase secretion. Furthermore, anionic surfactants exhibited stabilizing effect on the enzyme during preservation at 4°C. Conclusions: PEG 8000 and the ionic detergents (SDS, cholic acid and Tween‐80) were more effective in the solubilization of cell membrane components, and enhancing enzyme yields than the cationic detergents such as CTAB (N,Cetyl‐N,N,N‐trimethyl ammonium bromide). Further, these surfactants were found to stabilize the enzyme at 4°C. Significance and Impact of the Study: The secretion of Ca2+‐independent hyperthermostable α‐amylase was enhanced in the presence of certain anionic and non‐ionic detergents in the medium. Furthermore, the surfactants stabilized the enzyme during preservation at 4°C. The use of this enzyme in starch hydrolysis eliminates the addition of Ca2+ in starch liquefaction and its subsequent removal by ion exchange from sugar syrups.