Executive Summary : | Despite several efforts on identifying potent plastic-degrading microbes and -hydrolyzing enzymes from various impacted habitats, very few studies have been successful, and many have yielded inefficient results. One major barrier is microbe adaptation to plastic-impacted niches, evolution of efficient plastic degradative pathways, and targeted development of hydrolytic enzymes at impacted sites. Because plastic polymers are new to the environment and are resistant, non-reactive, highly hydrophobic, and non-biodegradable, they have not exerted enough selection pressure on natural communities to evolve efficient pathways and enzymes. As a result, finding potent plastic hydrolysing enzymes from any site that has not been subjected to long selection pressure or a long history of plastic pollution appears to be a difficult task. In addition, many plastic polymers are found to be inaccessible to enzyme (promiscuous) active sites because of thermodynamic constraints. For example, in polyethylene terephthalate (PET), the carbonyl group of carboxylic esters is contributed directly from aromatic ring and hence pose thermodynamic constraints for enzymes to hydrolyse the ester linkages. So, studies on screening plastic degrading microbes from landfill sites with long history of plastic waste dumping would help in rationalizing plans for discovering plastic hydrolysing microbes with efficient metabolic pathways and enzymes. In this context, landfill sites in Gujarat (Pirana, Ankhleswar, Bharuch, as major dumping yard since 1980s) over an area of ~ 118 ha with a total of ~5500 Mt solid waste disposed serves to be a rational and relevant site for exploring efficient plastic degrading microbes and their enzymes. Majority of the research on landfill microbiome conducted so far have focused primarily on cultivable communities, whereas integrated studies on site-specific microbial signatures including their metabolic and enzymatic potential are still limited. On the other hand, no such information is available on landfill site-specific plastic degrading enzymes at these dumpsites, demarcating it to be a major knowledge gap in terms of discovering novel plastic-hydrolysing enzymes for enhanced biodegradation. The current study aims to characterize polyethylene (PE) and polyethylene terephthalate (PET) [one of the major plastic waste, 40-50% of total waste] degrading indigenous microbial communities from three major landfill sites in Gujarat, with long history of plastic waste dumping (positive selection pressure). Since, phthalate isomers (isophthalate and terephthalate) are the structural constituent of PET polymer and have similar carboxyl-ester groups as that of PET polymer, these compounds would be used (as a direct proxy) for guiding evolution of PET-hydrolyzing enzymes by enriched community. Similarly, role of surfactants (Tween and SDS) are yet to be explored for enhancing the rate of polyethylene (PE) hydrolysis by PE-enriched community. |