Isolation and Characterization of Starch Degrading Rhizobacteria

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 indicia (DJUMC) respectively. Soil samples were serially diluted in sterilized peptone water; poured on sterilized starch agar plates, and incubated at 32ºC for 48h. The representative colonies shown 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 bacteria, rod shaped, while 15(28%) were Gram-negative rod shaped bacteria. Based on the biochemical tests, the results revealed that, the 38 isolates were belonging to the genera Bacillus while the remaining isolates were belonging to the genera Pseudomonas. All isolates were catalase positive and only 15 isolates (Pseudomonas) were KOH positive and were negative to grow at 80ºC, 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 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).