Distinct bacterial communities affiliated with two types of shredder-produced particles in streams

Leaf litter decomposition is a vital ecosystem process in which macroinvertebrate-shredders produce substantial amounts of fine particulate organic matter (FPOM) via sloppy feeding and defecation, creating a substratum and substrate for microbial assemblages. However, microbial communities colonizing the shredder-produced FPOM are understudied compared to those in streams and on original leaves. Here, we investigated the bacterial community composition on shredder-produced FPOM in a laboratory experiment. We fed alder, beech, and maple leaves conditioned under oxic or anoxic conditions to Sericostoma (Insecta: Trichoptera) larvae. We collected shredded leaf particles and faecal pellets as shredder-produced FPOM at different times and examined their microbial communities using 16S rRNA amplicon sequencing. We hypothesized that shredder-produced FPOM types harbor diverse, distinct, and specialized microbial taxa in response to leaf species and conditioning. We found significantly higher alpha diversity on shredded leaves compared to faecal pellets. Microbial communities on faecal pellets differed from initial leaf communities and with anoxic and oxic conditioning. Bacterial communities developing on leaves were dominated by common leaf decomposers including Flavobacterium and Pseudomonas whereas faecal pellets harbored gut bacterial taxa including Acinetobacter and Carnobacterium. These results underline the importance of conditioning and shredder activity in shaping FPOM-attached bacterial communities, increasing bacterial diversity in stream ecosystems.