The Biodegradation of Polystyrene by Soil Bacteria

Abstract

The myriad of useful applications of plastic are ubiquitous across every aspect of modern life. Resistance to degradation, the hallmark property of many plastics including polystyrene, is paradoxically one of plasticâs greatest threats to the environment. This study will focus on polystyrene, a plastic used in many private and commercial applications as a foam or solid. Studies dating back to the 1970âs indicate polystyrene does not easily degrade naturally; thus polystyrene waste swept into the sea, found discarded within terrestrial ecosystems, or deposited in landfills persists in these environments for innumerable years impacting delicate ecosystems. In this study, soil bacteria species were screened for polystyrene degradation activity in order to reveal potential pollution intervention approaches. Soil microbes were recovered directly and by enrichment growth on Styrofoam packing peanuts. After single colony isolation on yeast extract peptone glucose (YEPG) agar, candidate microbes were grown in liquid carbon-free phosphate minimal medium (PMM) upon ninety-six well polystyrene plates for three weeks. Potential degrader status was assigned to isolates growing on polystyrene plastic dishes, (e.g. the sole carbon source), using a metabolic indicator dye that oxidizes a colorless substrate to a yellow color, water soluble tetrazolium (WST-1). Several intrinsic factors complicated the interpretation of this strategy including bacterial spore formation, stored carbon within polysaccharides, and metabolism of trace materials impregnated in polystyrene during manufacture. Mixed bacterial isolates were examined for sustained metabolic activity. Additional metabolic assessments included a candidate microbeâs (2C73) use of monomeric styrene as a carbon source, and the influence of plant root exudates on metabolism and growth. A direct screening for survival and replication of 2C73 growing onStyrofoam packing peanuts was conducted, with subsequent foam mass reduction noted. We isolated and characterized several rhizosphere bacteria from a residential site and an industrial site in terms of survival and growth on a polystyrene petri-dish (the sole carbon source). Candidates were characterized using WST-1, and colony forming units present after incubation in polystyrene as the only carbon source. 16S rDNA sequence analysis was utilized to determine genus. In summary: These results suggest some soil-borne bacteria have potential to motivate soil-born polystyrene degradation.