Sediment trap preservative choice impacts particle‐associated microbial community composition

Abstract Understanding and quantifying the microbial contribution to particulate organic matter (POM) flux and carbon cycling in the ocean relies largely on the collection of sinking POM. A critical aspect of evaluating microbial communities on sediment trap‐collected POM is their preservation until recovery and sample processing. While RNA later has emerged as a recent preservative in sediment trap studies, no comparisons have been made between RNA later and the more established preservative, formalin, to determine their effectiveness in capturing POM‐attached microbial communities. Our work evaluates these preservatives through laboratory testing and sediment trap deployments (lasting days to months). Formalin‐fixed POM required decrosslinking (undoing bonds between DNA and proteins) to extract DNA. When decrosslinking was included, no community differences were observed from subsequent DNA extraction or amplification when preserved in the lab. However, when preservatives were deployed inside sediment traps, significant differences were observed among unpreserved, RNA later ‐preserved, and formalin‐preserved POM. In these samples, some copiotrophs, such as Gammaproteobacteria, Verrucomicrobiae, and Flavobacteria, demonstrated greater relative abundances in RNA later , and the overall magnitude of these differences was greater for RNA later ‐preserved vs. formalin‐fixed POM, indicating differing abilities of each preservative to halt microbial activity, contributing to the overrepresentation of some taxa. Together, these results suggest that formalin preservation is the best option for use in sediment traps, especially for long‐term deployments (> 5 d), common for moored sediment trap timeseries studies. A skewed view of microbial community structure on POM has implications for our understanding of the taxa and metabolisms contributing to carbon turnover in the ocean.