Microbial communities associated with plastic mulch debris in agricultural soils

Currently, plastic mulch debris represent one of the main sources of microplastic pollution in agricultural soils. However, there is still limited research on plastic and microorganisms' interaction in terrestrial agroecosystems as compared to marine ecosystems. In this study, we have characterized the microbial communities associated with agricultural plastic mulch debris by using culture-dependent, and culture-independent (i.e., high-throughput DNA sequencing) approaches. Weathered plastic mulch debris samples were collected from the topsoil of five agricultural fields in Baza, Granada province in southern Spain, characterized by intensive horticultural production over the last ten years. The bacterial communities from the plastisphere soil (soil tightly adhered to the plastic) as well as the community tightly attached to the plastic surface were assessed by estimating the culturable populations by dilution plating on general media and the total (culturable and non-culturable) populations by NGS analysis of 16S rRNA amplicons. Additionally, all the plastic samples were characterized by FTIR spectroscopy and identified as polyethylene. The results from the culturable approach showed a significantly higher number of colony-forming units in the plastisphere soil than on the plastic surface, revealing some differences among field plots. Furthermore, 16S rRNA amplicon sequencing showed that the bacterial alpha-diversity, as measured by Richness index was higher in the plastisphere soil. Beta diversity Weighted-UniFrac index indicated that the main significant differences in the bacterial communities occurred among field plots, which might be related to the soil type, and/or crop history, and a lower effect of the plastic niche sampled. Some genera such as Arthrobacter, Bacillus, Blastococcus, Kocuria, Nocardioides, Sphingomonas, and Streptomyces were present in high abundance on both plastisphere soil and plastic surface from all the assessed fields. Furthermore, in one of the fields, the genera Polycyclovorans and Bdellovibrio showed significantly higher abundance in the plastic surface than in the plastisphere soil, indicating in this case a selective effect of the plastic for specific bacterial genera. Further research is still needed to better understand the potential impacts of plastic pollution on terrestrial agroecosystems as well as the complex interaction between plastic and microorganisms.

“This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 955334 - SOPLAS.”