Identification and characterization of thermophilic amylase producing bacterial isolates from the brick kiln soil

The present experiment was designed to isolate bacterial strains from the brick kiln soil and to check the activity and enzyme kinetics of amylase from these isolates. The bacterial colonies were isolated from soil samples through the serial dilution method. The bacterial isolates were identified through morphological, electron microscopic and molecular analysis. The 16S ribosomal RNA sequences of the isolates IR-1, IR-2, IR-3, IR-8, and IR-9 showed high similarities with Bacillus tequilensis, Bacillus paramycoides, Proteus alimentorum, Bacillus wiedmannii, and Pseudomonas aeruginosa, respectively. All of the bacterial isolates showed a positive catalase activity except IR-9. Furthermore, the isolates showed variable antagonistic effects against different bacterial pathogens. All of the strains produced indole acetic acid (IAA), and the concentrations increased in the presence of tryptophan application. The isolates showed the amylase enzyme activity and maximum activity of isolates was achieved in 4% starch concentration. The IR-9 isolate showed the highest amylase activity of 5.9 U/ml. The V-max values of the extracellular amylase from different bacterial isolates ranged between 12.90 and 50.00 IU ml(-1). The lowest K-m value of 6.33 mg starch was recorded for IR-8 and the maximum K-cat value of 2.50 min(-1) was observed for IR-3. The amylase activity of the isolates was significantly affected by a range of different incubation time, temperature, and pH values. Further tests are required before the potential utilization of these isolates for amylase production, and in the biopesticide and biofertilizer applications. (C) 2020 The Authors. Published by Elsevier B.V. on behalf of King Saud University.