Identification and Characterisation of Amylolytic Bacteria from Tuber and Cereal Processing Units and Dumpsites in Kumasi

Amylases are enzymes essential for commercial and industrial purposes in breaking down starch to soluble sugars. In Ghana, commercial amylases are absent though there is abundance of starchy materials in which amylase-producing bacteria inhabit. Therefore, this study was to identify and characterize amylolytic bacteria in cereal and tuber processing units and dumpsites in Kumasi using morphological and biochemical methods. Using a 3 x 3 Factorial experiment with three (3) replications using Completely Randomized Design (CRD), eighteen samples from three starchy sources, namely, cassava, maize, and rice were aseptically collected from three processing and waste dumpsites in Kumasi. Bacteria were morphologically and biochemically screened from the various substrates, rate of bacteria growth was determined and enzyme activities of the enzymes produced by the organisms were ascertained. Cluster analysis and multivariate analysis were conducted on the data obtained. Not all the substrates had the organisms, rice had highest while maize had the lowest making maize not suitable in producing amylase. A total of 50 bacteria isolates were identified which were grouped into 10 classes on the basis of the similarity in their qualitative characteristics where five were amylolytic and five were non-amylolytic. All bacteria were Gram positive and catalase positive. Across the three fermentation systems, only pH of substrate was significantly different (P < 0.05) whereas temperature and oxidation-reduction potential (ORP) were not. The pH of starch substrates ranged between 4.68 ± 0.58 and 6.45 ± 0.54, temperature ranged between 26.83 ± 0.93 and 27.67 ± 1.25 oC, and ORP ranged between 72.5 ± 113.20 mV and 134.5 ± 24.50 mV. A cluster analysis based on Dice similarity index grouped the five amylolytic populations into two large clusters, cluster I and cluster II (with sub clusters A, B, and C). The clusters were putatively identified as Staphylococcus spp. for cluster I and IIC, Bacillus spp. for cluster IIA, and Pseudomonas spp. and Staphylococcus spp. for cluster IIB. Mean ivzone of clearance across the four isolates was 5.39 ± 0.17 mm for 24-h incubation which increased to 7.44 ± 0.13 mm for 48 h of incubation. Significant growth of the bacteria cells were recorded for all isolates at 37 oC, pH 7.0, and 1.0% starch concentration with isolate IIA showing the highest growth across the various parameters. There were differences in the activities of the enzymes produced by the organisms, where Bacillus spp. had the highest followed by Pseudomonas spp. and Staphylococcus spp. Across the various isolates, optimum enzyme activity of 7.20 ± 0.30 to 12.60 ± 0.20 U/mL was exhibited at 75 oC whereas optimum activity of 5.55 ± 0.30 to 11.7 ± 0.20 U/mL was demonstrated at pH 7.0, 4.20 ± 0.30 to 9.30 ± 0.20 U/mL displayed at 1.0% substrate concentration, and 43.50 ± 4.00 to 88.50 ± 5.00 U/mL at 96 h of incubation. However, in an economic sense for industrial purposes, the 72 h incubation period can be used since enzyme activities at the said incubation time is not different from 96 h. These findings suggest that bacteria are good sources of amylase and good for industrial purposes. However, further studies are required to identify the species of the bacteria and its associated enzymatic properties such as thermostability. Moreover, the type of amylase produced needs to be ascertained.

Source: KNUST