Bacteriome consistency in a parasitic worm: variation throughout the life cycle and across geographic space

Microbial communities within metazoans are increasingly linked with development, health and behaviour, possibly functioning as integrated evolutionary units with the animal in which they live. This would require microbial communities to show some consistency both ontogenetically, i.e. across all the animals life stages, and geographically among populations. Here, we characterise the bacteriome of the parasitic trematode Philophthalmus attenuatus, which undergoes major transitions throughout its life cycle, and test whether it is consistent on developmental and spatial scales. Based on sequencing the prokaryotic 16S SSU rRNA gene, we compared the parasite bacteriome across three life stages, i.e. rediae in snails, cercariae exiting snails, adults in birds in one locality, and among three geographic localities for the redial stage only. Knowledge of helminth microbiomes is still limited at present. However, microbes carried by parasites can influence parasite virulence and modulate host-parasite interactions, therefore elucidating their origins and the spatial and temporal variation in microbiome composition is of central importance for our understanding of disease dynamics and evolution.