Complex nitrogen cycling in the sponge Geodia barretti

Area of Science:

• Marine Microbiology
• Biogeochemical Cycles
• Symbiotic Microbial Ecology

Background:

• Marine sponges host diverse microbial communities, crucial for nutrient cycling in ecosystems like coral reefs and deep-sea environments.
• Sponges regulate internal oxygen, creating niches for both aerobic and anaerobic microbes, yet their microbial processes remain poorly understood.
• The nitrogen cycle, particularly nitrification, denitrification, and anammox, is vital for marine nutrient dynamics.

Purpose of the Study:

• To quantify aerobic (nitrification) and anaerobic (denitrification, anammox) nitrogen cycling processes within the marine sponge Geodia barretti.
• To identify the microbial players involved in these nitrogen transformation processes using molecular techniques.
• To assess the role of sponges in marine nitrogen budgets and nutrient recirculation.

Main Methods:

• Quantification of nitrification rates by measuring nitrite and nitrate production.
• Stable isotope incubation experiments using (15)NO(3)(-) and (15)NH(4)(+) to determine denitrification and anammox rates.
• Molecular identification of microbes via amplification of specific genes (amoA, 16S rRNA, nirS).

Main Results:

• High nitrification rates (566 nmol N cm(-3) sponge day(-1)) were observed, with ammonia-oxidizing Archaea and Nitrospira detected.
• Significant denitrification rates (92 nmol N cm(-3) sponge day(-1)) and anammox rates (3 nmol N cm(-3) sponge day(-1)) were measured.
• Microbial communities included denitrifiers (Betaproteobacteria) and anammox bacteria (Candidatus Scalindua spp.).

Conclusions:

• This study provides the first evidence of both anammox and denitrification occurring simultaneously within a single sponge host.
• Marine sponges facilitate complex microbial interactions, efficiently utilizing and recirculating nutrients via coupled aerobic and anaerobic processes.
• Sponges act as significant, previously unrecognized nitrogen sinks in marine environments, potentially influencing ocean nutrient dynamics more than sediments.