Extractive fermentation for enhanced gellan-hydrolysing enzyme production by Bacillus thuringiensis H14

Abstract

A new extractive fermentation process using PEG and potassium phosphate aqueous two-phase system (ATPS) was developed for enhanced production of gellan-hydrolysing enzyme by Bacillus thuringiensis H14. Five different Bacillus sp. were tested for their ability to synthesize gellan-hydrolysing enzyme. Bacillus thuringiensis H14 was found to be the best organism for gellan-hydrolysing enzyme production. The enzyme showed maximum activity at pH 7.5 and 40°C. The partition studies of gellan-hydrolysing enzyme in the system using PEG X (X = 9000, 6000, 4000) and potassium phosphate-water and PEG-sodium citrate-water system indicated that PEG (4000)-potassium phosphate-water is the best system for partitioning of gellan-hydrolysing enzyme into the PEG phase (K = 4.99). Gellan-hydrolysing enzyme production by Bacillus thuringiensis H14 was studied in ATPSs composed of PEG X (X = 9000, 6000, 4000) and potassium phosphate. The top phase is continuous and rich in PEG while the bottom phase is dispersed and is rich in phosphate, microbial cells being mainly retained in the bottom phase. The gellan-hydrolysing enzyme produced during fermentation partitioned into the upper PEG phase and total gellan-hydrolysing enzyme produced was 2.12, 2.29 and 2.40 times higher than that of homogeneous fermentation when the fermentations were carried out using PEG 9000-potassium phosphate-water, PEG 6000-potassium phosphate-water, PEG 4000-potassium phosphate-water systems respectively.