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Abstract
The need for an alternative to inorganic fertilizer is on the increase owing to the drawbacks associated with inorganic fertilizers. This study was therefore carried out to evaluate the bacteriological profile of digestates from different waste streams and the ability of the isolates to promote the growth of plants. Standard bacteriological methods were used to analyze digestates from different waste streams. Total heterotrophic bacterial count was obtained using pour plate method. The cultural, morphological and biochemical characteristics of the bacterial isolates were evaluated using standard differential media along with appropriate reagents. Plant growth promoting capacity of the isolates were evaluated using standard protocols for nitrogen fixation, phosphate solubilization, indole acetic acid and ammonia production. The results obtained from this study revealed that the total heterotrophic bacterial count (Log10 cfu/g) of digestate from different waste streams had values, which ranged from 4.91±0.02 for cattle rumen digestate to 4.41±0.03 for a combination of cattle rumen fruit and food waste digestate. The cultural, morphological and biochemical characteristics of bacterial isolates revealed the presence of Enterobacter cloacae, Escherichia coli, Pseudomonas aeruginosa, Salmonella enterica, Proteus mirabilis and Bacillus cereus. The distribution of bacterial isolates in the different waste streams revealed that E. coli was present in all digestates obtained from different waste streams. All bacterial isolates were found to possess plant growth promoting properties with 100 % capacity for nitrogen fixation and phosphate solubilization. While 66.7 % of the isolates had the ability to produce ammonia and indole acetic acid. The phosphate solubilization index of the isolates revealed that E. coli (5.97) and P. aeruginosa (5.76) had the highest solarization index amongst all tested bacteria in the study
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