Production of a high maltose-forming, hyperthermostable and Ca²⁺- independent amylopullulanase by an extreme thermophile <i style="">Geobacillus thermoleovorans</i> in submerged fermentation

Abstract

Production of a hyperthermostable, high maltose-forming and Ca²⁺-independent amylopullulanase by an extreme thermophile <i style="">Geobacillus thermoleovorans</i> was studied in submerged fermentation. Parametric optimization led to secretion of amylopullulanase (2850 U L^-1 of <img src='/image/spc_char/alpha.gif'> -amylase, 840 U L^-1 of pullulanase) in a starch-yeast extract medium (2% starch, 0.1% ammonium sulphate, 0.3% yeast extract, 0.1% K₂HPO₄, 0.1% NaCl, 0.01% MgSO₄.7H₂O and 0.1% Maltose) using 2% inoculum (12 h) at 70°C and 200 rpm in 20 h. The addition of trace elements, detergents, surfactants and additives did not stimulate growth or enzyme production. The hydrolysis of pullulan and starch yielded maltotriose, and maltose, maltotriose and maltotetraose as the major end products, respectively. The cultivation of the organism in a laboratory fermenter showed (i) abolition of the lag phase, (ii) a 2-fold increase in enzyme production (5880 U L^-1 of <img src='/image/spc_char/alpha.gif'> -amylase, 1900 U L^-1 of pullulanase) and (iii) a reduction in fermentation time to 7-8 h.