Degradation of trehalose by rhizobia and characteristics of a trehalose-degrading enzyme isolated from Rhizobium species NGR234

AIMS: This study was designed to examine the breakdown of trehalose by rhizobia and to characterize the trehalose-degrading enzyme isolated from Rhizobium sp. NGR234. METHODS AND RESULTS: Rhizobium sp. NGR234, Rhizobium fredii USDA257, R. phaseoli RCR3622, R. tropici CIAT899 and R. etli CE3 showed good growth in the presence of carbohydrate. Validamycin A did not prevent the growth of NGR234 on trehalose. The expression of a trehalose-degrading enzyme by NGR234 was intracellular and inducible by trehalose. The isolated enzyme digested other disaccharides, p-nitrophenyl-alpha-d-glucopyranoside and the substrate. The enzyme showed optimum activities at pH 7.0 and 30 degrees C. Its pI was 4.75 and the V(max) of the enzyme occurred at 35.7 micromol s(-1) mg(-1) protein with the K(m) of 23 mmol when trehalose was hydrolysed. CONCLUSIONS: An enzyme capable of breaking down trehalose was produced. Some of the properties of the trehalose-degrading enzyme are similar to those isolated from other organisms but, this enzyme was validamycin resistant. These rhizobia like other trehalose-degrading microbes use trehalose by enzymatic catabolic action. SIGNIFICANCE AND IMPACT OF THE STUDY: Trehalose which accumulates during legume-rhizobia symbiosis is toxic to plants. Detoxification by trehalose-degrading enzymes is important for the progress of symbiosis.