Isolation and characterization of starch degrading rhizobacteria from soil of Jimma University Main Campus, Ethiopia

Starch degrading bacteria are important for different industries such as food, fermentation, textile, and paper. The aim of this study is to isolate and characterize bacteria able to degrade starch from the rhizospheres of various plants at four sites located in Jimma University main campus. Collected soil samples were labeled as kobo (AJUMC), Avocado (BJUMC), Banana (CJUMC), and Cana indica (DJUMC) respectively. Soil samples were serially diluted in sterilized peptone water, poured on sterilized starch agar plates, and incubated at 32ºC for 48 h. The representative colonies showing different morphology was randomly picked up using the streaking method on nutrient agar. A total of 53 bacterial isolates were obtained from the soils rhizospheres. Microscopic characteristics showed that among the 53 isolates, 38 (72%) were Gram-positive rod shaped bacteria, while 15 (28%) were Gram-negative rod shaped bacteria. Based on the biochemical tests, the results revealed that the 38 isolates belonged to the genera Bacillus while the remaining isolates belonged to the genera Pseudomonas. All isolates were catalase positive and only 15 isolates (Pseudomonas) were KOH positive with negative growth at 80°C, while the 38 (Bacillus) isolates have positive growth at 80ºC. The highest values of starch degrading index were the Gram positive bacteria isolates. The amylase activity was also carried out with respect to time, temperature and pH of the media. The maximum activity of amylase at different temperatures from 35 to 45°C was recorded at 35°C (0.94 U/ml) within 24 h, while maximum activity at different pH from 5 to 9 was recorded at pH 7 (1 U/ml).