Microplastics exert minor influence on bacterial community succession during the aging of earthworm (Lumbricus terrestris) casts

• Published in: Soil biology & biochemistry Vol. 195; p. 109480
• Main Authors: Meng, Ke, Harkes, Paula, Huerta Lwanga, Esperanza, Geissen, Violette
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.08.2024
• Subjects: Active bacterial community; Cast aging; Cast physicochemical properties; Earthworm gut content; Lumbricus terrestris; Microplastics; Cast aging; Microplastics; Earthworm gut content; Active bacterial community; Cast physicochemical properties; Lumbricus terrestris
• ISSN: 0038-0717; 1879-3428
• DOI: 10.1016/j.soilbio.2024.109480

The soil microbiome, which is shaped by gut-related activities of earthworms, is affected by microplastic contamination. However, the influence of microplastics on earthworm gut and cast microbiomes has been poorly explored. Here, we investigated the influence of microplastics (1% in soil, w/w) on soil physicochemical properties and bacterial communities during gut passage and cast aging of Lumbricus terrestris. Microplastics used in agricultural film production were selected, i.e., low density polyethylene, polylactic acid and polybutylene adipate terephthalate (PBAT). Different niches, including pre-ingestion soil, gut content and aged casts (from 0 to 180 days), were studied. Results showed that microplastics possibly enhanced the gut passage-derived difference between pre-ingestion soil and fresh cast in terms of pH, ammonium, nitrate and nitrite, and dissolved organic carbon. But such effects mostly faded out after 180 days of aging. The composition, as well as the alpha and beta diversity of both the total (DNA) and active (RNA) bacterial communities were decisively shaped by their niche (R2: 0.22–0.63, p < 0.001, PERMANOVA), rather than the presence/absence or the types of MPs. Nevertheless, biomarkers indicative of PBAT treatment were identified, and functional prediction for the active community showed that bacterial communities of this treatment had higher potentials for hydrocarbon degradation (4.9–7.8 times that of the microplastic-free treatment in gut and aged casts). We also identified a “Soil-related core community” and a “Gut-related core community” (contributing to 39.2%–50.2% of the cast microbiome), which possibly neutralized microplastic impacts and maintained the structure and function of bacterial communities during the soil–gut–cast transit. Our findings indicate that the tested microplastics exerted a minor influence on the bacterial communities during the cast aging process, microplastics in aged casts might not necessarily have significant additional influence on the soil microbiome when they are incorporated into soils. Future studies testing different soils, polymers, and earthworm species, under field conditions are recommended to help enhance current knowledge of the influence of microplastics on earthworm cast microbiomes. [Display omitted] •Microplastics (MPs) influence on the aging of earthworm casts was studied.•MPs affected the physicochemical properties of fresh casts but not in the long term.•PBAT MPs had minor influence on the active community (RNA).•Soil- and Gut-related core communities were likely to buffer the impacts of MPs.•MP-containing casts may not cause additional effects on the soil microbiome.