A Thermostable Extracellular α-amylase from Bacillus licheniformis Isolated from Cassava Steep Water

Screening and Characterization of Thermostable Amylase-Producing Bacteria Isolated from Soil Samples of Afdera, Afar Region, and Molecular Detection of Amylase-Coding Gene

Studying thermostable amylase-producing bacteria in extreme environments has a crucial role to overcome different industrial challenges. Afar Region is one of the hottest and salty areas, making it the home of extremophiles. This study aimed at screening and characterizing amylase-producing bacteria isolated from soil samples of Afdera, Afar Region, and detection of their amylase-coding genes. Thus, a total of 49 bacterial isolates were obtained from the collected soil samples. Out of these, three isolates (M2, M8, and M13) were selected on the basis of diameter of the average clear zone formation and time taken to decolorize iodine solution. Based on their morphological and biochemical characteristics, the isolates were identified as genus Bacillus. PCR amplification and detection of the amylase-coding gene confirmed the presence of the amylase gene in the three bacterial isolates. Optimum amylase production time for these isolates was 48 hrs (M13 and M8) and 72 hrs (M2) corresponding to the amylase activity of 0.67 U/mL for M13, 0.74 U/mL for M8, and 0.73 U/mL for M2 with an optimum temperature of 55°C. Studies on the effect of temperature revealed that the crude enzyme had a maximum activity and stability at 75°C, 70°C, and 65°C for isolates M13, M8, and M2, respectively. Additionally, amylase produced from all isolates retained more than 66.41% of their original activity after incubating them at a temperature range from 55 to 80°C for 50 min. Optimum pH for the activity of all crude amylases was in the range from 5 to 9 with a peak activity at pH 8. Their activity decreased significantly by the presence of Zn⁺² and Mg²⁺; however, their activity increased by the presence of Ca⁺². Moreover, the three crude amylases were stable (0–3 M) with NaCl concentration. Amylases of this finding with thermophilic and halophilic characteristics offer a wide range of applications in food, brewing, textile, starch, paper, and deterrent industries. Thus, identification of these Bacillus isolates at a molecular level and purification as well as detailed characterization of the types of amylases are recommended for effective utilization in different industries.

Purification and Characterization of Natural Solid-Substrate Degrading and Alcohol Producing Hyperthermostable Alkaline Amylase from Bacillus cereus (sm-sr14)

OBJECTIVE

Amylases enzymes hydrolyze starch molecules to produce diverse products including dextrins, and progressively smaller polymers. These include glucose units linked through α-1- 1, α-1-4, α-1-6, glycosidic bonds.

METHODS

This enzyme carrying an (α /β) 8 or TIM barrel structure is also produced containing the catalytic site residues. These groups of enzymes possess four conserved regions in their primary sequence. In the Carbohydrate-Degrading Enzyme (CAZy) database, α-amylases are classified into different Glycoside Hydrolase Families (GHF) based on their amino acid sequence. The present objective was to study one such enzyme based on its molecular characterization after purification in our laboratory. Its main property of solid-natural starch degradation was extensively investigated for its pharmaceutical/ industrial applications.

RESULTS

Amylase producing bacteria Bacillus cereus sm-sr14 (Accession no. KM251578.1) was purified to homogeneity on a Seralose 6B-150 gel-matrix and gave a single peak during HPLC. MALDITOF mass-spectrometry with bioinformatics studies revealed its significant similarity to α/β hydrolase family. The enzyme showed an efficient application; favourable Km, Vmax and Kcat during the catalysis of different natural solid starch materials. Analysis for hydrolytic product showed that this enzyme can be classified as the exo-amylase asit produced a significant amount of glucose.

CONCLUSION

Besides the purified enzyme, the present organism Bacillus cereus sm-sr14 could degrade natural solid starch materials like potato and rice up to the application level in the pharmaceutical/ industrial field for alcohol production.