Bacteria and Yeasts Isolated from the Environment in Biodegradation of PS and PVC Microplastics: Screening and Treatment Optimization

Biodegradation is the most environmentally friendly and, at the same time, economically acceptable approach to removing various pollutants from the environment. However, its efficiency in removing microplastics (MPs) from the environment is generally low. The successful biodegradation of MPs requires microorganisms capable of producing enzymes that degrade MP polymers into compounds that the microorganisms can use as a source of carbon and energy. Therefore, scientists are screening and characterizing microorganisms that can degrade MPs more efficiently. These microorganisms are often isolated from sites contaminated with MPs because the microorganisms living there are adapted to these pollutants and should be able to better degrade MPs. In this study, five bacterial strains and five yeast strains were isolated from various environmental samples including activated sludge, compost, river sediment, and biowaste. Among them, screening was performed for bacteria and yeasts with the highest potential for the biodegradation of polystyrene (PS) and polyvinyl chloride (PVC) MPs, and the bacterium Delftia acidovorans and the yeast Candida parapsilosis were identified as the best candidates. Optimization of biodegradation of the selected MPs by each of these two microorganisms was performed, focusing on the influence of cell density, agitation speed and pH of the medium. It was found that within the selected experimental ranges, high values of cell density, low agitation speed, and a slightly basic medium favored the biodegradation of PS and PVC MPs by Delftia acidovorans. In the case of Candida parapsilosis, favorable conditions also included high cell density followed by a slightly higher, but not maximum, agitation speed and a weakly acidic medium. Broad spectroscopic and imaging methods indicated that Delftia acidovorans and Candida parapsilosis better adapt to PVC MPs to use it as a carbon and energy source.