Characterization of a β-amylase from Propionicimonas sp. ENT-18 ectosymbiont of Acromyrmex subterraneus brunneus

Abstract

The last decade has seen an increase in the industrial use of amylase, mainly due to its role in the production of anhydrous ethanol through the hydrolysis of corn starch. Most amylases in use nowadays are isolated from microorganisms, indicating their potential as a source of amylases for industrial applications. Since most microbial diversity remains unknown, microbes associated with previously undiscovered niches can provide an untapped source of new molecules. We investigated the diversity of actinobacteria associated with an underexploited niche and have identified a number of rare actinobacteria. We further aimed to characterize the amylase produced by one such actinobacterium, Propionicimonas sp. ENT-18, an ectosymbiont associated with the integument of Acromyrmex subterraneus brunneus. Our data indicate that this actinobacterium produces a high-molecular-weight β-amylase (170.4 kDa), with maximum production at the end of the log phase (96 h at 28°C) when cultured in Starch-Czapek broth. The maximum specific activity (50 mU/mg protein) was obtained at pH 5.5 at 30°C. The β-amylase produced was partially purified by ice-cold acetone precipitation, with a recovery of 65% activity. Although this enzyme has not shown any special trait (e.g., thermal or pH stability) for industrial applications, this is the first report of a β-amylase-producing Propionicimonas. © 2011 Springer-Verlag and the University of Milan.