Delayed preservation of marine invertebrates during field sampling may impact microbiome characterization. Here, we show that a 3-h preservation delay decreased microbiome richness in the ascidian Trididemnum solidum; however, menthol addition mitigated diversity loss and overall microbiome composition was not significantly altered, as dominant taxa remained intact. Thus, we report minimal impacts of short-term preservation delay on ascidian microbiomes and show that the common practice of menthol treatment before preservation can counteract minor microbiome shifts associated with processing delays.

Obligate symbioses present challenges for functional genetic analysis. This study shows that antisense inhibition cannot be used to investigate gene functions in the aquatic symbiosis between Bodo saltans and its bacterial symbiont. Our work stresses the importance of the development of alternative protocols to study the biology of both the microeukaryote and the associated bacterium.