Assessment of the enzymatic and biodegradation potentials of polyethylene degrading microbes isolated from two composite sites

Abstract

This study investigated the viability of composting for actively breaking down synthetic polymer nylon by fungal and bacteria species. A total of thirty (30) samples were taken over the course of three months from two composting sites that contained different coloured polyethylene bags. The identification and characterization of isolates was done using morphological and biochemical techniques while the Analytical Profile Index (Biomeuriex API kit) was used to confirm the identities of the isolates. The overall load of heterotrophic bacteria varied between 3.30 x 10⁴ cfu/g to 1.50 x 10⁶ cfu/g, while that of fungi ranged from 1.02×10⁴sfu/g to 1.26×10⁶sfu/g. Pseudomonas sp. showed the highest prevalence (30%), followed by Staphylococcus sp. (16%). The least frequently occurring bacteria were Micrococcus varians and Proteus mirabilis (4% each). The most common species of fungi were Aspergillus niger (25%) and Fusarium sp. (23.33%), while Aspergillus candidus exhibited the lowest prevalence (3.33%). There was an increase in the temperature of the compost from 24° C to 29 °C in the two sites and an increase in the pH from 6.7 to 7.7. The percentage reduction in weight of white nylon is 6.7% in site 1 and 6.4 % in site 2, the blue nylon reduced by 9% in site 1 and 8.5% in site 2. There was 8.1% loss in weight in yellow nylon in site 1 and 7.5% weight loss in site 2. The black nylon reduced in weight by 8.7% in site 1 and 8.1% in site 2. The enzyme activity showed Fusarium sp. (++) and Aspergillus niger (++) having the highest cutinase activity while the lowest activity was observed in the bacteria. It can be concluded that the combined activity of microorganisms and their enzymes play a major role in the biodegradation of polyethylene which is a major nuisance in the environment.