Exoteric and cryptic nitrogen, sulfur cycling in sponges along the oxic-anoxic continuum

Sponges are considered to be one of the most ancient lineages of metazoans and are believed to have emerged amongst these early branching animal lineages at a time before the oceans became fully oxic around the middle to late Neoproterozoic Era (850-542 Mya).

Sponges appear to retain some sort of ancestral memory of the hypoxic milieu from which they evolved and can still tolerate harsh hypoxic or anoxic conditions for relatively long periods.

They express specialized anaerobic pathways that have been mostly lost in higher order animals such as fish and mammals, and yet remnants of these pathways persist primarily in the way they use the endogenously generated gases hydrogen sulfide and nitric oxide (NO) as signaling molecules for cellular homeostasis or as key players in cytoprotection during periods of hypoxic stress.

Extensive sequencing of sponge microbiomes has primarily demonstrated the ubiquitous presence and expression of sponge symbiome pathways involved in NO generation via ammonia-oxidation and denitrification as well as the oxidation of reduced sulfur compounds, hinting at an active anaerobic lifestyle within sponges.

Experimental demonstrations of these processes are rare in sponge holobionts and lacking in sponges sensu stricto who also express the relevant anerobic energy metabolisms.

I will thus aim to demonstrate, disentangle, and integrate sponge holobiont metabolisms along the oxic-anoxic continuum by combining my expertise in sponge holobiont biogeochemistry and metabolic pathways with the expertise of the host in sponge physiology, nano-oxic O2 measurements at multiple spatial scales and dimensions, and advanced bioimaging techniques.

The proposed multimethod and interdisciplinary study will thus provide an unprecedented view of sponge holobiont metabolism at the thermodynamic limit of animal life thereby providing further insights into higher animal responses to hypoxia and the future of animal life on a planet experiencing ocean deoxygenation.