Marine Sponge Archaea Exhibit Metabolic Versatility, Utilizing Amino Acids Alongside Ammonia

A team from the University of Vienna, in partnership with colleagues in Australia, has found that the ammonia‑oxidizing archaea inhabiting marine sponges are not the limited specialists once thought. Rather, these microorganisms possess a wider metabolic toolkit, easily metabolizing amino acids in addition to their usual ammonia source.

Conducted by microbiologists Bettina Glasl and Katharina Kitzinger, the research combined metagenomic sequencing, lab incubations and isotope‑tracing techniques to track the feeding preferences of the sponge‑dwelling archaea. Results showed that, in the presence of amino acids, the archaea integrated these compounds into their metabolism while still maintaining their primary function of ammonia oxidation.

Such adaptability questions the traditional notion that ammonia‑oxidizing archaea (AOA) are obligate chemolithoautotrophs dependent exclusively on inorganic nitrogen. Within the intricate sponge microhabitat, where levels of dissolved organic matter vary, toggling between inorganic and organic nitrogen could grant the symbionts a competitive edge, sustaining their activity across shifting conditions.

These results carry wider significance for grasping nitrogen cycling in marine environments. Sponges harbor rich microbial communities that play a major role in converting nitrogen species in coastal seas. Should a notable share of their AOA also metabolize organic nitrogen, the overall impact on nitrogen fluxes might be more complex than present models suggest.

Upcoming studies will seek to measure the prevalence of this “flexitarian” trait across various sponge species and additional marine settings. Identifying the genetic mechanisms that permit the shift between ammonia and amino‑acid use may also illuminate the evolutionary forces driving microbial symbioses. This work adds another dimension to our understanding of marine nitrogen dynamics and highlights the need to re‑evaluate assumptions regarding the metabolic inflexibility of pivotal microbes.