Preliminary Investigation On Marine Bacteroides Promoting Settlement And Metamorphosis Of Sponge Larvae

Marine sponges are ancient multicellular animals that has been interacted with microbes for more than 600 million years.As an important holobiont,sponge has become the typical animal to learn about interactions between marine microbes and their animal hosts.Larval settlement and metamorphosis is essential for the development of sponges and is the important stage related to the ontogeny and the distribution for sponge adults.As an important part of the sponge holobiont,the roles of microorganisms that played in larval development remain unknown.The previous research showed that the abundance of Bacteroides changed drastically from the planktonic stage to the settlement stage of the sponge.Therefore,this research focuses on interactions between Bacteroides species and sponge Tedania sp.during the process of swimming-settlement.Firstly,thirteen bacterial species(12 genera within 3 classes)isolated from marine sponge revealed a common ability to significantly promote larval settlement at rates 30.00-53.33%higher than control groups(p<0.05).Secondly,Bacteroidetes species evolved three effective strategies to promote larval settlement:(ⅰ)two strains formed biofilms enhancing the settlement rate to 56.67-63.33%within three days.(ⅱ)five strains secreted hydrosoluble molecules improving larval settlement,reaching 59.17%.(ⅲ)extracellular vesicles(EVs)produced by Bacteroidetes strains were effective structures that significantly improved settlement by up to 86.67%(p<0.05).Thirdly,the EVs marked by fluorescence under the confocal laser scanning microscope demonstrated that they initially attached to the larva and then transported from the surface into the inner layer of larvae from the planktonic to settlement stage.They then migrated together with cells to the outer layer,thereby contributing to metamorphosis.Finally,by metabonomic analysis of EVs and the joint analysis with sponge transcriptome,it was found that some neurotransmitter receptors were absent in sponges unlike other invertebrates with primary neural networks.And possibly the nitric oxide signal pathway was an important and ubiquitous pathway among the settlement process of marine sponge.EVs may promote larval settlement by transporting arginine,while the specific mechanism remains unknown.Generally,marine sponges specifically enrich Bacteroidetes species because of the important player in host development by forming biofilms,secreting chemical cues and producing EVs.The results would broaden the insight into the interaction between microbes and host in aspect of animal development,and establish the basis for reciprocal adaptive co-evolution between the microbial community and animals,evenincluding higher organisms.