Seasonal variation in the bacterial microbiome of questing nymphal ticks in Missouri, United States.

Background: Seasonal environmental variation may influence the composition of tick-associated bacterial communities. This study assessed seasonal differences in the microbiome of questing nymphal ticks collected from Missouri, United States. Methods: Questing ticks were collected during early and late seasonal periods at a livestock-associated site in central Missouri. To minimize confounding by developmental stage, microbiome analyses were restricted to nymphal ticks. Bacterial communities were characterized using 16S rRNA gene sequencing. Alpha diversity (richness, Shannon, and Simpson indices), beta diversity (Jaccard and Bray-Curtis dissimilarities), and differential abundance analyses were performed. Community differences were evaluated using permutational multivariate analysis of variance (PERMANOVA). Results: Sequencing generated 984-101,293 reads per sample. Sequencing depth was strongly correlated with observed richness ( Conclusion: Seasonal differences in bacterial community composition were detected among nymphal ticks despite similar levels of microbial richness and alpha diversity. The enrichment of a Rickettsia-associated ASV in early-season ticks suggests that season may influence the occurrence of specific bacterial taxa within tick microbiomes. Further studies using higher-resolution sequencing and pathogen-specific approaches are needed to clarify the ecological significance of these seasonal patterns.