Functional Transcripts Indicate Phylogenetically Diverse Active Ammonia-Scavenging Microbiota in Sympatric Sponges

Symbiotic ammonia scavengers contribute to effective removal of ammonia in sponges. However, the phylogenetic diversity and in situ activity of ammonia-scavenging microbiota between different sponge species are poorly addressed. Here, transcribed ammonia monooxygenase genes (amoA), hydrazine synthase genes (hzsA), and glutamine synthetase genes (glnA) were analyzed to reveal the active ammonia-scavenging microbiota in the sympatric sponges Theonella swinhoei, Plakortis simplex, and Phakellia fusca, and seawater. Archaeal amoA and bacterial glnA transcripts rather than bacterial amoA, hzsA, and archaeal glnA transcripts were detected in the investigated sponges and seawater. The transcribed amoA genes were ascribed to two Thaumarchaeota ecotypes, while the transcribed glnA genes were interspersed among the lineages of Cyanobacteria, Tectomicrobia, Poribacteria, Alpha-, Beta-, Gamma-, and Epsilonproteobacteria. In addition, transcribed abundances of archaeal amoA and bacterial glnA genes in these sponges have been quantified, showing significant variation among the investigated sponges and seawater. The transcriptome-based qualitative and quantitative analyses clarified the different phylogenetic diversity and transcription expression of functional genes related to microbially mediated ammonia scavenging in different sympatric sponges, contributing to the understanding of in situ active ecological functions of sponge microbial symbionts in holobiont nitrogen cycling.