Uncovering gut microbial diversity in Ligidium woodlice and its correlation with Rickettsiella.

BACKGROUND: Woodlice are a key group of macroarthropods in soil ecosystems, performing crucial ecological functions mediated by their microbiota. The gut microbial diversity has been investigated in several woodlice species, but the gut bacterial flora of the genus Ligidium remains unexplored. This study aims to characterize gut microbial diversity in Ligidium and its related influencing factors, thereby supporting their potential application as bioindicators for monitoring soil ecosystem health and enhancing bioremediation strategies. METHODS: The gut microbiota of 102 terrestrial isopod samples representing 12 Ligidium species was characterized by high-throughput sequencing of the 16 S rRNA V3–V4 region using the Illumina NovaSeq platform. Microbial community analyses were performed using QIIME2 (v.2022.11) based on SILVA Release 138 database. Statistical analyses (PERMANOVA, PERMDISP and Spearman correlations) were conducted to examine ecological patterns. RESULTS: Our analysis of intestinal contents from 102 Ligidium samples identified 2,781 amplicon sequence variants dominated by Actinomycetota (55.6%), Pseudomonadota (40.6%), and Bacillota (1.2%). The gut bacterial composition showed significant differences among Ligidium species. Host species was the primary driver shaping the gut microbial community structure in Ligidium, explaining 43.28% of variation. Geographic factors act as significant substantial variables, accounting for approximately 36.3% of the explained variation. The high abundance of Rickettsiella explained about 12.58% of community variation and emerged as the main source of intraspecific heterogeneity, as indicated by a 51.3% reduction in the PERMDISP F-value after it was removed. Furthermore, a significant negative correlation between the Rickettsiella relative abundance and the Shannon diversity index (Dataset 3: ρ =-0.2108, p < 0.05; dataset 4: ρ=-0.2648, p < 0.01), supporting the association of high Rickettsiella abundance with the reduced gut microbial diversity. CONCLUSION: As a key detritivorous isopod in undisturbed leaf litter ecosystems, Ligidium is anticipated to harbor exceptionally high gut microbial richness, reflecting its specialized saprophagous niche. This study presents the first comprehensive, multi-sample and multi‐species analysis of gut microbial diversity in Ligidium, revealing that host species is the primary determinant of microbial community structure, while geographical habitat and Rickettsiella significantly contribute to inter‐group variation. Spearman correlation analysis demonstrated a significant negative correlation between the Rickettsiella relative abundance and the Shannon diversity index. The high Rickettsiella abundance was associated with the reduced gut microbial diversity and altered the community composition.