Structural and functional characteristics of the microbial community emerging upon its contact with extruded polystyrene waste

Increasing plastic pollution is a serious environmental problem as widespread production and inadequate disposal of plastic materials lead to adverse impacts on ecosystems. The research investigated the structural and functional features of the anaerobic microbial community in contact with waste from extruded polystyrene (XPS) under methanogenic (MG), nitrate-(NR) and sulfate-reducing (SR) conditions. It has been shown that the presence of XPS in the microbial community does not have a negative effect on the processes of biogas formation, but, on the contrary, leads to an increase in the yield of methane and volatile fatty acids and a change in their ratio. Microparticles of different sizes were found in the culture fluid of variants with XPS: in NR conditions ‒ 2.4 × 106/ml, in SR conditions ‒ 1.2 × 106/ml and in MG conditions ‒ 0.4 × 106/ml, while in control variants microparticles was not found. Using scanning electron microscopy, it was revealed that in all experimental variants the surface of the polymer became looser, more textured, and irregularities, cracks and holes appeared. Increased diversity in the microbial community, associated with an increase in the number of microbial morphotypes, correlates with the results of high-throughput sequencing of the 16S rRNA gene. When XPS was introduced into an anaerobic community incubated in different donor-acceptor conditions, the number of groups of microorganisms included in it increased and the proportion of representatives of hydrolytic and acidogenic bacteria (Sedimentibacter, Lentimicrobium), acetogenic syntrophs (Syntrophomonas, Desulfovibrio, Geobacter) and methanogenic archaea (Methanosarcina, Methanobacterium) increased. Our study shows that waste from XPS is not inert for the microbial community and contact with it leads to significant changes in its structure and functioning. However, since the experiments were carried out using household XPS containing various fillers in addition to the main polymer, there is a possibility that, along with polystyrene, additional substances included in its composition (plasticizers, dyes, etc.) are also subject to degradation. The ability of microorganisms to destroy the polymer itself requires further research.