Elsevier

Bioresource Technology

Volume 102, Issue 7, April 2011, Pages 4925-4929
Bioresource Technology

Short Communication
Optimization of culture conditions for Aspergillus sojae expressing an Aspergillus fumigatus α-galactosidase

https://doi.org/10.1016/j.biortech.2011.01.036Get rights and content

Abstract

Using Response Surface Methodology, carbon and nitrogen sources and agitation speed for cultivation of Aspergillus sojae expressing the α-galactosidase gene, aglB of Aspergillus fumigatus IMI 385708 were optimized. Compared to cultivation in modified YpSs medium, cultivation in 250-mL Erlenmeyer flasks agitated at 276 rpm and containing 100 mL of optimized medium consisting of 10.5% molasses (w/v) and 1.3% NH4NO3 (w/v), 0.1% K2HPO4, and 0.005% MgSO4·7H2O achieved a 4-fold increase in α-galactosidase production (10.4 U/mL). These results suggest the feasibility of industrial large scale production of an α-galactosidase known to be valuable in galactomannan modification.

Introduction

α-Galactosidase (α-d-galactoside galactohydrolase; EC 3.2.1.22) is an exoglycosidase found in many microorganisms, plants and animals (Dey and Pridham, 1972). The enzyme has technological applications including treatment of molasses to remove raffinose (Kobayashi and Suzuki, 1972), hydrolysis of galactooligosaccharides in legume based foods to improve their nutritional quality and modifications of guar-gum-based gels (Dey et al., 1993). Some α-galactosidases can catalyze transgalactosylation reactions, especially at a high substrate concentration (Hashimoto et al., 1995). The Aspergillus fumigatus IMI 385708 α-galactosidase catalyzes the efficient transgalactosylation of a variety of monosaccharides, disaccharides and oligosaccharides including maltooligosaccharides, cellooligosaccharides and mannooligosaccharides. (Puchart and Biely, 2005). The A. fumigatus α-galactosidase also has the ability to debranch polymeric legume seed galactomannans, and the degree of polymeric galactomannan degalactosylation was the highest among the microbial α-galactosidases and approached that of enzymes from plants (McCleary, 1979, McCleary, 1983).

Since A. fumigatus is an opportunistic pathogen (Martinez et al., 2000), its α-galactosidase was expressed in the GRAS organism, A. sojae and yields of 2.45 U/mL were achieved (Gurkok et al., 2010). To increase the yield of the enzyme, response surface methodology was employed to optimize three factors important to enzyme production, carbon and nitrogen source and agitation speed.

Section snippets

Strain, media, and cultivation

Aspergillus sojae ATCC11906 (pyrG-), kindly supplied by Dr. P.J. Punt (TNO Nutrition and Food Research, Department of Microbiology, The Netherlands), was grown on glucose-containing modified YpSs agar (Cooney and Emerson, 1964) with 10 mM uridine and 10 mM uracil supplementation. Modified YpSs broth (4 g/L yeast extract, 1 g/L K2HPO4, 0.5 g/L MgSO4·7H2O, and 20 g/L glucose) without uridine and uracil supplementation was used as the basal medium for the enzyme production by recombinant A. sojae (A.

Selection of best carbon and nitrogen sources

Maximal α-galactosidase production of 4.5 U/mL was obtained with molasses (p < 0.05) (Fig. 1) likely because of beneficial effects of the complex composition of this carbon source which contains trace elements such as, magnesium, potassium, sodium, calcium, iron, copper (El-Abyad et al., 1992) and trace amounts of other carbohydrates in addition to the sucrose as the major carbohydrate. Molasses was thus chosen as carbon source for media optimization.

The difference in α-galactosidase production in

Conclusion

In this study, the improvement of α-galactosidase production by A. sojae Ta1 has been reported. The individual and interactive roles of carbon and nitrogen sources and agitation speed on α-galactosidase and biomass production were investigated by RSM using Box-Behnken Design. The results revealed that, inexpensive and simple medium compositions under efficient cultivation conditions can be manipulated to increase the enzyme yield up to 4-fold and gave insight for further studies regarding large

Acknowledgements

This work was supported by grants from State Planning Agency of Turkey and Middle East Technical University.

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