Engineered Alcaligenes sp. by chemical mutagen produces thermostable and acido-alkalophilic endo-1,4-β-mannanases for improved industrial biocatalyst

Abstract

This study reported physicochemical properties of purified endo-1,4-β-mannanase from the wild type, Alcaligenes sp. and its most promising chemical mutant. The crude enzymes from fermentation of wild and mutant bacteria were purified by ammonium sulfate precipitation, ion exchange and gel-filtration chromatography followed by an investigation of the physicochemical properties of purified wild and mutant enzymes. β-mannanase from wild and mutant Alcaligenes sp. exhibited 1.75 and 1.6 purification-folds with percentage recoveries of 2.6 and 2.5% and molecular weights of 61.6 and 80 kDa respectively. The wild and mutant β-mannanase were most active at 40 and 50 °C with optimum pH 6.0 for both and were thermostable with very high percentage activity but the wild-type β-mannanase showed better stability over a broad pH activity. The β-mannanase activity from the parent strain was stimulated in the presence of Mn²⁺, Co²⁺, Zn²⁺, Mg²⁺ and Na⁺. V_max and K_m for the wild type and its mutant were found to be 0.747 U//mL/min and 5.2 × 10^-4 mg/mL, and 0.247 U/mL/min and 2.47 × 10^-4 mg/mL, respectively. Changes that occurred in the nucleotide sequences of the most improved mutant may be attributed to its thermo-stability, thermo-tolerant and high substrate affinity- desired properties for improved bioprocesses.

Keywords: chemical mutagenesis; kinetic parameters; metal ion tolerance; pH and thermostability; purification and characterization; β-mannanase.