Gut Microbes May Help an Alien Snail Settle Into East China

The decollate snail, Rumina decollata, is a Mediterranean species that humans have spread across North and South America, Africa and Asia, and it is considered invasive in several of those introduced regions. In eastern China, however, its populations are still formally regarded as alien rather than established invaders. A new study in the journal NeoBiota asked what might help this snail persist in unfamiliar surroundings, and it turned to an often-overlooked candidate: the community of bacteria and fungi living in the animal’s gut.

Researchers led an investigation in Nanjing, China, where Rumina decollata lives alongside two native terrestrial snails, Acusta ravida and Euphaedusa aculus. The team collected snails from three contrasting habitats: Pailou Lane, an urban residential quarter; the campus of Nanjing Forestry University; and Fangshan Park, a mountain park. Twelve individuals of the alien snail were gathered at each site. Because individual snail guts yield very little tissue, the midgut and hindgut of two snails from the same habitat were pooled into a single biological replicate, producing six replicates per habitat and eighteen in total for metagenomic sequencing.

The study combined two sequencing strategies. Shotgun metagenomics of the eighteen pooled gut samples catalogued the full functional potential of the microbial genes present, while amplicon sequencing of the bacterial 16S rRNA gene and the fungal internal transcribed spacer region compared the gut communities of all three snail species with the surrounding soil at the sympatric campus site. Before sequencing, all snails were starved for forty-eight hours in sterile containers to empty their guts and limit cross-contamination, and dissections were performed under sterile conditions.

The metagenomic results showed that the broad functional framework of the gut microbiome stayed largely conserved across habitats, but specific metabolic pathways shifted with location. Overall functional profiles differed significantly among the three sites, and pairwise comparisons showed that the mountain park population differed significantly from both the campus and the urban residential populations, while the campus and urban populations did not differ significantly from each other. Carbohydrate-active enzyme profiles, by contrast, showed substantial overlap among habitats and no statistically significant overall difference.

Within those broad patterns, targeted analyses revealed telling differences. Chitin-related functions were enriched in the mountain park population: the relative abundance of chitinase genes of the GH18 family was 5.72 percent there, compared with 4.74 percent at the campus and 5.32 percent at the urban site, and the chitin-binding module CBM14 followed the same trend. Chitin in terrestrial ecosystems can come from arthropod exoskeletons, fungal cell walls and other environmental sources, so this enrichment points to heightened microbial potential for processing chitin-containing substrates, although the authors caution that it does not directly identify what the snails actually eat.

The campus population, living in the most anthropogenically disturbed habitat, showed the opposite signature. Xenobiotic degradation pathways were most represented there, with the benzoate degradation pathway reaching 0.0375 percent of annotated abundance at the campus, versus 0.0158 percent at the urban site and 0.0092 percent at the mountain park. The campus microbiome also carried more pathways for environmental sensing and energy acquisition, including two-component systems and oxidative phosphorylation, along with membrane transport functions such as ATP-binding cassette transporters. The researchers interpret this as consistent with greater exposure to heterogeneous resources and chemical compounds in human-influenced environments, while stressing that contaminants were not directly measured, so the enrichment cannot be read as proof of pesticide exposure or adaptation to pollution.

The amplicon data told a complementary story about community composition. Bacterial and fungal communities were clearly separated by host species, and gut samples from all three snails clustered apart from the surrounding soil, indicating host-associated differentiation rather than simple pickup of environmental microbes. A permutational analysis of variance confirmed that group identity significantly explained variation in bacterial community composition, accounting for roughly 42 percent of the variation. The alien snail’s gut was dominated by genera such as Cutibacterium, Corynebacterium and Staphylococcus, and the fungal genus Malassezia was strongly enriched in its gut, patterns the authors suggest are consistent with stable host-associated assemblages rather than transient environmental contamination.

Notably, the gut microbiome of Rumina decollata partially overlapped with that of the native snail Acusta ravida, while Euphaedusa aculus stood further apart. The authors suggest this similarity may reflect shared ecological conditions or comparable plant-based resource use, since the decollate snail is described in earlier ecological work as a dietary generalist that can consume plant material, detritus, fungi and animal-derived resources, whereas the two native species are considered predominantly herbivorous or detritivorous. Rather than demonstrating complete ecological separation, the microbiome patterns are consistent with potential ecological differentiation that could help explain how the alien and native snails coexist in the same habitat.

A further layer of the analysis examined how bacteria and fungi relate to each other inside the gut. Although the two kingdoms coexist in the same organ, Procrustes analysis found no significant concordance between their overall community structures, suggesting their assembly is largely independent at the whole-community level. Yet cross-domain co-occurrence networks built from significant Spearman correlations revealed extensive positive associations between individual bacterial and fungal taxa, with more than 93 percent of significant correlations being positive. In the decollate snail’s own network, 157 nodes were connected by 874 edges organized into seven modules, and genera such as Staphylococcus, Malassezia and Aspergillus occupied highly connected positions. The authors interpret these patterns as co-occurrence rather than evidence of ecological interactions, since correlation-based analyses cannot establish biological mechanisms.

The study also screened for antibiotic resistance genes and virulence-associated functions, which had previously been reported in other invasive snails. Both were detected in the gut microbiome of Rumina decollata, although overall profiles of resistance genes and virulence factors did not differ significantly among the three habitats, with some individual resistance classes appearing at higher abundance in the campus group. The authors suggest this may reflect differences in environmental exposure rather than active host adaptation, and they flag these findings as warranting further investigation rather than drawing public health conclusions. They are equally candid about the study’s limits: environmental variables such as vegetation, soil properties and disturbance were not independently measured, host population structure was not assessed, and because no reference genome exists for Rumina decollata, host-read removal relied on the genome of the giant African snail as a surrogate, supplemented by conservative filtering against a microbial reference database. With those caveats in place, the work offers a microbiome-rooted perspective on invasion biology, portraying the gut community of this alien snail as functionally flexible across habitats yet taxonomically distinct from its surroundings, a combination the authors propose may be relevant to its persistence in East China.

Subject of Research: Gut microbiome variation in the alien snail Rumina decollata and its coexistence with native snails in East China

Article Title: Metagenomic and amplicon sequencing uncover adaptation and sympatric coexistence of the alien snail Rumina decollata (Linnaeus, 1758) ( Stylommatophora , Achatinidae ) with native terrestrial snails in East China

Article References: Xu, Y., Gao, M., Zhang, G., Li, Y., & Liu, H. (2026). Metagenomic and amplicon sequencing uncover adaptation and sympatric coexistence of the alien snail Rumina decollata (Linnaeus, 1758) (Stylommatophora, Achatinidae) with native terrestrial snails in East China. NeoBiota, 110, 21-41. https://doi.org/10.3897/neobiota.110.208923

Image Credits: AI Generated

DOI: 10.3897/neobiota.110.208923

Keywords: Rumina decollata, invasive species, gut microbiome, metagenomics, 16S rRNA, ITS amplicon sequencing, Nanjing, Acusta ravida, chitinase, xenobiotic degradation, antibiotic resistance genes, host-associated microbiota