Co-metabolic breakdown of LDPE microplastics in PGPR-Assisted phytoremediation of hydrocarbon-contaminated soil

Abstract

A 90-day pot study investigated the effect of low-density polyethylene microplastics (LDPE MPs) on bioaugmented phytoremediation of crude oil-contaminated soil using lemongrass (Cymbopogon flexuosus) and Micrococcus luteus WN01 (PGPR). Plant growth, root morphology, root exudates, microbial population, dehydrogenase activity, residual TPH concentration, and LDPE MP degradation were evaluated. M. luteus significantly increased plant biomass and improved TPH degradation by 79.16% and 64.43%, which were 25.04% and 15.85% higher than uninoculated treatments. M. luteus inoculation still led to higher TPH removal compared to uninoculated treatments despite MP-induced alterations in plant biochemical and morphological traits. GC/MS analysis of lemongrass root exudates showed that M. luteus enriched plants with GABA-associated allelochemicals. FTIR analysis indicated accelerated oxidation of LDPE MPs in planted treatments compared to unplanted ones, evidenced by increased absorbance at characteristic peaks (3620.71 cm⁻¹ O-H stretching, 1651 cm⁻¹ C=O stretching, and 1031.10 cm⁻¹ C-O stretching). This strongly suggests a co-metabolic breakdown of LDPE MPs within the plant rhizosphere (a degradation hotspot). Lemongrass essential oil was not significantly affected by the contaminant or M. luteus. This study highlights the lemongrass-M. luteus association as a promising candidate for the remediation of both petroleum- and MP-contaminated soil, with the added benefit of essential oil production.