Biodegradation of polyethylene by thermophilic bacteria Bacillus licheniformis and Streptomyces spp

Abstract

Plastic and polyethylene waste accumulating in the environment are posing an ever increasing ecological threat. The plastic sheets or bags do not allow water and air to go into earth, which causes infertility of soil, preventing degradation of other normal substances and danger to animal life. One of the most problematic plastics in this regard is polyethylene (PE). Isolation, screening and identification of the most efficient bacteria (Streptomyces spp. and Bacillus licheniformis) degrading linear low density polyethylene were obtained in the previous study. However, the factors that affect the degradation rate of PE were studied in this work. The selected isolates that can degrade polyethylene were found to degrade PE at pH 7-7.5. However, the optimum temperature was at 50 ﹾC and optimum agitation was at 150 rpm. The degree of polyethylene degradation was increased when Streptomyces spp. and Bacillus licheniformis were combined together. The activity of the bacterial biofilm could be measured by hydrolysis of fluorescein diacetate (FDA). It was found that Bacillus licheniformis colonized PE surface and formed a massive biofilm on it, thus the biofilm formation increased the biodegradability of the isolated Bacillus licheniformis than Streptomyces spp.