The biotransformation of isonicotinamide was investigated using thermophilic intracellular amidase produced from Geobacillus subterraneus RL-2a. Various process parameters, including amount of biocatalyst, substrate feeding rate, enzyme-to-substrate ratio and operational thermostability were systematically examined with the aim of achieving complete substrate conversion and high productivity. In 1 L fed batch reaction containing 0.1 M isonicotinamide, in 0.2 M potassium phosphate buffer (pH 6.5, 200 rpm) and 8 U ml(-1) amidase activity (12.48 mg dcw ml(-1)) of whole cells of G. subterraneus RL-2a (as biocatalyst) resulted in a yield of 0.1 M of isonicotinic acid after 50 min reaction time at 70 degrees C and a total of 61.55 g isonicotinic acid was produced at a rate of 1.18 g h(-1) g(-1) dcw respectively. The volumetric productivity was 14.8 g h(-1)l(-1). (C) 2015 Elsevier Ltd. All rights reserved.