Background:

Sponges are increasingly recognised as key ecosystem engineers in many aquatic habitats. They play an important role in nutrient cycling due to their unrivalled capacity for processing both dissolved and particulate organic matter (DOM and POM) and the exceptional metabolic repertoire of their diverse and abundant microbial communities. Functional studies determining the role of host and microbiome in organic nutrient uptake and exchange, however, are limited. Therefore, we coupled pulse-chase isotopic tracer techniques with nanoscale secondary ion mass spectrometry (NanoSIMS) to visualise the uptake and translocation of ¹³C- and ¹⁵N-labelled dissolved and particulate organic food at subcellular level in the high microbial abundance sponge Plakortis angulospiculatus and the low microbial abundance sponge Halisarca caerulea.

Results:

The two sponge species showed significant enrichment of DOM- and POM-derived ¹³C and ¹⁵N into their tissue over time. Microbial symbionts were actively involved in the assimilation of DOM, but host filtering cells (choanocytes) appeared to be the primary site of DOM and POM uptake in both sponge species overall, via pinocytosis and phagocytosis, respectively. Translocation of carbon and nitrogen from choanocytes to microbial symbionts occurred over time, irrespective of microbial abundance, reflecting recycling of host waste products by the microbiome.

Conclusions:

Here, we provide empirical evidence indicating that the prokaryotic communities of a high and a low microbial abundance sponge obtain nutritional benefits from their host-associated lifestyle. The metabolic interaction between the highly efficient filter-feeding host and its microbial symbionts likely provides a competitive advantage to the sponge holobiont in the oligotrophic environments in which they thrive, by retaining and recycling limiting nutrients. Sponges present a unique model to link nutritional symbiotic interactions to holobiont function, and, via cascading effects, ecosystem functioning, in one of the earliest metazoan–microbe symbioses.

This dataset was collected in an experiment run between June and Juy 2018. It contains extracted values from NanoSIMS data, which gives the Atom% carbon and nitrogen from different cells of interest in sponge tissue over time. The last tab contains bulk stable isotope data (from EA-IRMS) from the sponges used in the experiment. Included are isotopic enrichment of sponge tissue in delta notation and carbon and nitrogen content (%) and dryweight of the sponge tissue. From these values, incoporation rates of dissolved and particulate organic matter are derived, which are provided in the main text and supplementary materials. 

There are no missing values.