Nitrogen-and Carbon-cycling Microbes With Transcription Activity In Sponge Holobionts

Sponges are the ancient multicellular organisms in the ocean.They are widespread in the tropical,temperate and polar sea areas,and are the critical components of oceanic ecosystems.Diverse and abundant microbes have been found in sponge holobionts,which are thought to be one of the main drivers in the nitrogen and carbon cycles in the ocean.However,the diversity and activity status of the active sponge functional symbionts in nitrogen and carbon cycling is scarcely explored.Since sponge symbionts are complex and difficult to be isolated or cultivated,culture-independent molecular techniques have been used to uncover the transcribed genes of sponge symbionts in nitrogen and carbon cycling.Such applications would help to illustrate the compostion,diversity and ecological roles of the active functional community within sponges,and to reveal the symbiosis and flexibility mechanisms between sponge and microbes.In this investigation,16S rRNA and functional gene analyses at the transcriptome level revealed the active archaeal and bacterial communities,especially the diversity and transcription abundance of the nitrifying population in the South China Sea model sponge Theonella swinhoei.Result showed that,the nitrifying population was consisted of the ammonia-oxidizing archaea?AOA?Nitrosopumilus and nitrite-oxidizing bacteria?NOB?Nitrospira lineages and higher abundance of transcribed Nitrosopumilus amoA than that of Nitrospira nxrB fragments in the T.swinhoei transcriptome.Analysis and comparison of the transcribed genes from ammonia-scavenging microflora in the sympatric sponges T.swinhoei,Plakortis simplex and Phakellia fusca showed that,ammonia-oxidation gene amoA belonged to the Thaumarchaeota lineage and ammonia-assimilation gene glnA belonged to the Cyanobacteria,Tectomicrobia,Poribacteria and Proteobacteria lineages.Active AOA and ammonia-assimilating bacteria groups varied significantly among different sponges and differed between sponges and seawater.Abundances of the transcribed archaeal amoA and bacterial glnA fragments showed distinct variations among these sponges and were higher than that in seawater.These findings implied that,the active ammonia-scavenging microflora would be influenced by sponge species and biotopes?sponge or seawater?.Besides that,16S rRNA pyrosequencing and functional genes analyses at the transcription level unraveled the active bacteria community,especially the active CO₂-assimilation and CO-oxidation bacteria in the sympatric sponges T.swinhoei,P.simplex,P.fusca and ambient seawater.Results demonstrated that,composition of the active bacterial community showed significant variations among the investigated sponges and differed from that in seawater.Some bacteria would assimilate CO₂ via the reductive pentose phosphate cycle and the biotin carboxylation reaction pathways,and some other bacteria could oxidize CO via aerobic CO dehydrogenase-mediated pathway.Community structure of the active CO₂-assimilating bacteria or CO-oxidizing bacteria was remarkably influenced by sponge species and differed from that in seawater.This study implied that,sponge species and biotopes?sponge or seawater?would influence the community composition and diversity of the active ammonia-scavenging microflora.This investigation disclosed the active functional community involving carbon and nitrogen cycling in sponges,and revealed the influence of sponge species and biotopes on the composition,diversity and transcriptional activity of the functional communities.These findings implied that,some ecological functions would be performed by phylogentically diverse yet functionally equal community in sponges.This study would enhance the knowledge of composition features,active status and ecological functions of sponge uncultivated symbionts,and strengthen our understanding of the sponge–microbe symbiosis.