Permeabilization and inhibition of the germination of spores of Aspergillus niger for gluconic acid production from glucose

Author

SumitraRamachandranaPierreFontanilleaAshokPandeybChristianLarrochea

a

Laboratoire de Génie Chimique et Biochimique (LGCB), Polytech’ Clermont-Ferrand, Université Blaise Pascal, 24, Avenue des Landais, B.P. 206, F- 63174 Aubière Cedex, France

b

Biotechnology Division, National Institute for Interdisciplinary Science and Technology (formerly Regional Research Laboratory), CSIR, Trivandrum 695 019, India

Received 2 December 2006, Revised 17 May 2007, Accepted 21 June 2007, Available online 21 September 2007.

Abstract

In this study, the role of citral to permeabilize the spores of Aspergillus niger and replace sodium azide in the bioconversion medium was studied. Further, characterization of glucose oxidase of spores was carried out by exposing both permeabilized and unpermeabilized spores to different pressures (1, 2, 2.7 kb) and temperatures (60, 70, 80, 90 °C). Unpermeabilized spores after exposure to high temperatures were permeabilized by freezing before using as catalyst in the bioconversion reaction. Results showed that citral permeabilized the spores and could inhibit spore germination in the bioconversion medium. Rate of reaction was significantly increased from 1.5 to 4.35 g/L h which was higher than the commercial glucose oxidase 2 g/L h). Glucose oxidase activity of A. niger was resistant to pressure. However, pressure treatment could not permeabilize them. Behaviour of fresh and permeabilized spores to temperature varied significantly. Glucose oxidase activity of fresh spores exposed to high temperature was unaffected at 70 °C till 15 min and 84% of relative activity was retained even after 1 h at 70 °C while permeabilized spore got inactivated at 70 °C for 15 min, which followed the same pattern as commercial glucose oxidase. Cellular membrane integrity was lost due to permeabilization by freezing which resulted in heat-inactivation of glucose oxidase when spores were permeabilized before heat treatment. Thus, glucose oxidase of spore remains heat stable when unpermeabilized and active while permeabilized and its reaction rate is higher than the commercial glucose oxidase.

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