Bacterial and Archaeal 16S rRNA communities were assessed in the walls and surrounding sediment of Hediste diversicolor, and compared to the transitory community found within the gut tracts of these individuals.. Variations in sediment microbial assemblages during deposit feeder gut transit

Invertebrate activities in sediments regulate the structure and function of associated microbial assemblages. Through ingestion, gut passage, and excretion of the sediment substrate, deposit-feeding invertebrates expose microbial assemblages to variations in organic matter and redox conditions. Currently, we only have a limited understanding of how gut passage affects the structure of these transitory assemblages, and how this might impact sediment functioning. Using high-throughput sequencing and quantitative PCR, we assessed how gut passage through the marine polychaete Hediste diversicolor affected bacterial and archaeal assemblage structure, and the abundance of nitrogen cycling taxa, by comparing samples taken from the sediment, external polychaete surface, and gut sediment contents. Overall, unique transitory assemblages were identified within the digestive tract which, during gut passage, became more similar to the surrounding sediment assemblage. As similar taxa were enriched in both the hindgut and burrow wall, these transitory assemblages may contribute to the composition of the wider sediment assemblage. The hindgut was also a ‘incubator’ of unique ammonia-oxidising archaeal taxa with potential implications for sediment nitrogen cycling. Polychaete gut passage may therefore play a significant role in regulating sediment microbial assemblage composition and biogeochemical functioning.