Microplastics are increasingly polluting our environments. Yet, we still need to better understand their impact on the ecosystems and their inhabitants. The study “The effect of microplastic pollution on the gut microbiome of anecic and endogeic earthworms” in FEMS Microbiology Letters explores how plastic particles influence the growth and gut microbiomes of different earthworm species, as explained by Christina Papazlatani. #FascinatingMicrobes
Microplastic – the emerging pollution of soil ecosystems
Used plastics commonly end up in terrestrial and aquatic systems where they break down into small fragments (<5 mm), known as microplastics. Even though the effect of microplastic pollution has been extensively studied in marine ecosystems, their impact on terrestrial ecosystems remains largely underexplored, despite the fact that agricultural land may contain more microplastics than oceans.
One soil health indicator is the populations and diversity of earthworms as they participate in ecosystem services such as soil formation, water regulation, nutrient cycling and organic matter decomposition. Hence, these so-called soil ecosystem engineers impact the growth and productivity of other soil (micro)organisms and plants.
Based on their lifestyles, earthworms are categorized into three groups: epigeic worms live in the soil surface and feed from litter, while endogeic worms live inside the soil, produce horizontal burrows and feed on mineral soil, and anecic worms move between soil layers by creating vertical burrows, thus feeding on litter that they drag into their tunnels.
For the health and metabolism of earthworms, the worm’s gut microbiome is crucial as it helps digest food, hence material from the soil. The worm’s feces, the so-called cast, also plays an important role in soil ecosystem functions.
The earthworm lifestyle shapes its gut microbiome
Similar to the microbial communities of other hosts, the composition of the earthworms’ gut microbiome is affected by its environment and food intake. Especially soil pollutants and microplastic consumption were shown to impact gut microbial communities of epigeic earthworms. However, it is not clear how the gut microbiomes of anecic and endogeic earthworms are affected by plastic.
That’s why the study “The effect of microplastic pollution on the gut microbiome of anecic and endogeic earthworms” in FEMS Microbiology Letters aimed to understand how microplastics impact their lifestyles. For this purpose, the endogeic grey worm Apporectodea caliginosa and the anecic common earthworm Lumbricus terrestris were incubated in soils with and without low-density polyethylene microplastics for 55 days. At the end of the incubation period, the gut microbiome composition was analysed.
The two earthworm species had distinct gut microbiomes. The endogeic Apporectodea caliginosa hosted plentiful and diverse bacterial communities that mostly comprised of the phyla Firmicutes, Actinobacteriota and Proteobacteria accounting for 90.4% of the total microbial community. On the family level, Bacillaceae and Micrococcaceae were highly abundant.
On the contrary, Lumbricus terrestris’ gut was dominated by the Firmicutes phylum which comprised of about 70% of the total microbial community. Contrary to endogeic earthworms, the Peptostreptococcaceae, Clostridiaceae and Enterobacteriaceae families were dominating.
Microplastics affect earthworms’ gut microbiomes
The microplastics did not seem to impact the growth and survival of either tested earthworm. Nevertheless, their gut microbiomes showed clear shifts in the presence of microplastics.
In Lumbricus terrestris, microplastics induced higher abundance of 7 bacterial strains belonging to Firmicutes phylum and Clostridiaceae, Peptostreptococcaceae and Lachnospiraceae families. In contrast, in Apporectodea caliginosa, 9 bacterial strains were abundant in the presence of microplastics belonging to diverse families of the phyla Proteobacteria, Plactomycetota, Actinobacteriota and Nitrospirota.
In both cases, bacterial phyla of potential plastic degraders were enriched. Notably, Firmicutes and Actinobacteria were previously shown to degrade low density polyethylene microplastics.
Previous research on the effects of microplastics on earthworms’ gut microbiomes have so far been contradictory, with some reporting strong effects and others none. Therefore, this helped elucidate how microplastic pollution impacts the gut microbiome and overall performance of earthworms. Moreover, it offered a prospective source of potential plastic degraders which could be a useful tool to confront microplastic pollution in soil ecosystems.
- Read the article “ Effect of microplastics pollution on the gut microbiome of anecic and endogeic earthworms” by Papazlatani et al. in FEMS Microbiology Letters (2024).
Christina Papazlatani is Postdoctoral fellow at the department of Microbial Ecology in the Netherlands Institute of Ecology (NIOO). Ever curious about the effect of microbial interactions on the macrocosm, she decided from early on to pursue an academic researcher career. She is currently a member of Dr. Paolina Garbeva’s group where she studies sustainable approaches to control plant pathogenic fungi by employing the indigenous soil microbial community. Her research interests revolve around sustainable agriculture and reducing the effect of anthropogenic pollutants in terrestrial ecosystems.
About this blog section
The section #FascinatingMicrobes for the #FEMSmicroBlog explains the science behind a paper and highlights the significance and broader context of a recent finding. One of the main goals is to share the fascinating spectrum of microbes across all fields of microbiology.
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