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

Abstract

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.

The Potential of AOP Pretreatment in the Biodegradation of PS and PVC Microplastics by Candida parapsilosis

“…It is expected that microorganisms inhabiting an MP-rich environment are already adapted to MPs and that they are more efficient in biodegrading plastic polymers than microorganisms that avoid such environments. The same report [47] shows that Candida parapsilosis has the highest potential for biodegrading PS and PVC MPs compared to other yeast cultures isolated from the same environment. The biodegradation experiments were carried out under conditions described as optimal in the same report.…”

“…For example, they have a much higher metabolic rate [45], and filamentous fungi can secrete specific proteins, so-called hydrophobins, which facilitate the adhesion of their hyphae to hydrophobic surfaces [46]. Regarding the biodegradation of PS MPs by fungi, we found, in one of our previous studies [47], that the yeast Candida parapsilosis has the potential to degrade PS and PVC MPs. As far as we know, there are no other reports in the literature on the treatment of PS MPs with yeasts, but only with molds and white-rot fungi [48][49][50][51][52][53][54][55].…”

“…The yeast Candida parapsilosis was selected for the biodegradation experiments. The yeast was isolated from an MP-rich environment and cultivated as described in detail in one of our previous reports [47]. It is expected that microorganisms inhabiting an MP-rich environment are already adapted to MPs and that they are more efficient in biodegrading plastic polymers than microorganisms that avoid such environments.…”

Evaluation of Fenton, Photo-Fenton and Fenton-like Processes in Degradation of PE, PP, and PVC Microplastics

“…The RSM approach involves a series of mathematical techniques aimed at building an empirical model that describes the relationship between the input variables (i.e., the independent variables) and one or more dependent variables (i.e., the response) [52]. Based on our experience in the field of optimization of pollutant degradation in the aquatic environment [53,54], we have assumed that a quadratic model represented by Equation (11) should be sufficient to describe the system with three independent variables and one dependent variable.…”

“…The model coefficients are denoted by a, while x 1 to x 3 represent the values of the three process parameters tested: pH, mass ratio of MPs to iron, and mass ratio of H 2 O 2 to iron. In addition to the linear (x 1 , x 2 , x 3 ) and quadratic (x 1 2 , x 2 2 , x 3 2 ) contributions, the model also includes the interaction terms (x 1 x 2 , x 1 x 3 , x 2 x 3 ) to cover the possible combined effects of the parameters tested, which, as we knew from experience [53][54][55][56][57], are not uncommon in such systems. The area of a broad FTIR band that occurred in the spectral range 3000-3600 cm −1 was used as the response, i.e., as the dependent variable y.…”