Marine Sponge Archaea Exhibit Metabolic Flexibility, Utilizing Both Amino Acids and Ammonia

Researchers from the University of Vienna, in collaboration with Australian partners, have found that the ammonia‑oxidizing archaea inhabiting marine sponges are not the narrow specialists once presumed. Instead, these microbes possess a wider metabolic toolkit, readily employing amino acids alongside their traditional ammonia substrate.

The project, led by microbiologists Bettina Glasl and Katharina Kitzinger, combined metagenomic sequencing, laboratory incubations and isotope tracing to follow the nutritional choices of the sponge‑associated archaea. The experiments demonstrated that when amino acids were supplied, the archaea incorporated them into their metabolism without abandoning their core ammonia‑oxidizing function.

This adaptability challenges the long‑standing view that ammonia‑oxidizing archaea (AOA) are strict chemolithoautotrophs dependent solely on inorganic nitrogen. Within the complex microenvironment of a sponge, where dissolved organic matter can vary, the ability to toggle between inorganic and organic nitrogen sources may grant a survival edge, allowing the symbionts to remain active under fluctuating conditions.

The results have broader implications for our understanding of nitrogen cycling in marine ecosystems. Sponges host dense microbial consortia that play a major role in converting nitrogen compounds in coastal waters. If a substantial portion of their AOA can also process organic nitrogen, the overall impact on nitrogen fluxes could be more nuanced than current models predict.

Future investigations will aim to quantify how widespread this “flexitarian” behavior is among different sponge species and other marine habitats. Pinpointing the genetic triggers that enable the switch between ammonia and amino‑acid utilization could also shed light on the evolutionary pressures shaping microbial symbioses. The study adds another layer to the picture of marine nitrogen dynamics and underscores the need to revisit assumptions about the metabolic rigidity of key microbial players.