Isolation and identification of plastics-degrading microorganisms from soils of Morogoro, Tanzania

Abstract

Plastics, though widely used, have low biodegradability and hence are persistent in the environment, becoming a major source of pollution. The study herein was conducted to isolate, from soils, isolates of microorganisms capable of biodegradation of plastics. The soils were sampled from Morogoro Municipality in Tanzania. The pH of the soils ranged between 6.46 and 8.91. Organic carbon ranged from 0.20 and 1.23%, which was very low to low. Total nitrogen ranged from 0.01 and 0.09%, which was very low. Textures of the soils used were sandy, loamy sand and sandy clay loam. Isolation and the enumeration of bacteria, fungi and actinomycetes (Streptomyces) was done using nutrient agar, potato dextrose agar and starch casein agar, respectively. The total populations of microorganisms ranged from 1.60 x 104 to 1.57 x 105 CFU/g soil. The capability of microbial isolates to biodegrade ground polyethylene bags and bottles was tested using Bushnell and Haas agar. Many isolates were capable of degrading plastics as depicted by the diameters of clear zones around colonies, ranging between 1.0 and 66 mm for ground polyethylene bags and 1.0 to 73.7 mm for ground plastic bottles. Using molecular methods, identified bacterial isolates were Bacillus cereus and Cellulosimicrobium sp. Fungal isolates identified were Eupenicillium rubidurum, Phoma sp., Neosartorya fischeri, Aspergillus terreus, Talaromyces islandicus and Aspergillus sp. Actinomycetes were Streptomyces werraensis and Streptomyces rochei. Selected identified isolates showed significant (P≤0.05) differences in ability to degrade the plastics, with Bacillus cereus, Streptomyces rochei, and Phoma sp., being most efficient, with diameters of clear zones ranging, overall, from 30.0 to 66.0 mm for fungi and 19.3 to 47.5 mm for bacteria and actinomycetes. Further studies are needed to identify more isolates capable in degrading the different types of plastics which are routinely disposed of in the Tanzanian environment.