Seawater is a dense microbial suspension with >106 prokaryotic and >104 eukaryotic propagules per milliliter. Hence, submerged surfaces get immediately covered by biofilm-forming colonizers upon contact with sea...Seawater is a dense microbial suspension with >106 prokaryotic and >104 eukaryotic propagules per milliliter. Hence, submerged surfaces get immediately covered by biofilm-forming colonizers upon contact with seawater. Since biofilms may reduce individual fitness through decreasing motility and attractiveness or increasing shearing stress by water currents and infection risk by pathogens, marine organisms have evolved countermeasures to regulate the number of surface-colonizers;alternatively they tolerate settlement and biofilm-formation. Antimicrobial defense mechanisms co-evolved with potentially colonizing microbes. By contrast, non-native animals (neozoa) are confronted with novel microbial colonizers upon colonizing a new habitat, and are expected to be less well protected against surface-colonization. Here we present results of a thorough screening of the epithelial surface of the ctenophore Mnemiopsis leidyi, being non-native in European marine environments, for epithelial bacteria and archaea. Neither light- and electron-microscopic inspection nor PCR-screening for bacterial and archaeal DNA of 134 adult specimens from different collection sites in the Western Baltic revealed any presence of prokaryotes on the surface epithelium of comb jellies in a recently invaded environment. A limited number of bacterial associates became evident from whole-body extracts of both juvenile and adult comb jellies. Their taxonomic diversity, however, was significantly lower in adult than in juvenile specimens, suggesting a maturation of anti-microbial defense upon ontogenetic development. The mechanisms underlying the effective defense of Mnemiopsisagainst microbial colonization, however, remain unknown. Based on our findings, we propose 1) to make use of invasion events as natural space-for-time experiments on how symbiotic interactions change upon environmental change;and 2) to study basal metazoan animals, such as ctenophores, to understand the evolutionary basics of symbiont-host interactions.展开更多
The Ediacaran Dickinsonia is well-known for being the only fossil to be assigned to many phyla, ranging from lichens, Cnidaria, Piatyheiminthes, Annelida, and a phylum of its own to a nonmetazoan kingdom. A new specim...The Ediacaran Dickinsonia is well-known for being the only fossil to be assigned to many phyla, ranging from lichens, Cnidaria, Piatyheiminthes, Annelida, and a phylum of its own to a nonmetazoan kingdom. A new specimen from the Ediacaran fine-grained sandstone on the Winter Coast of the White Sea in northern Russia, which has an age of -555 million years ago, preserved convincing internal anatomies of definite animals, comparable with meridionai canals of extant ctenophores （comb jellies）. Additionally, we reconsidered Dickinsonia as a biradiaily symmetrical animal rather than a bilateral one as previously thought. The animal nature of Dickinsonia is, thus, well established and its affinities are most probably allied to ctenophores. This research is not only removing Dickinsonia from Vendobionta, but also bringing the fossil record of ctenophores forward to 20 million years before the Cambrian ＂explosion＂.展开更多
文摘Seawater is a dense microbial suspension with >106 prokaryotic and >104 eukaryotic propagules per milliliter. Hence, submerged surfaces get immediately covered by biofilm-forming colonizers upon contact with seawater. Since biofilms may reduce individual fitness through decreasing motility and attractiveness or increasing shearing stress by water currents and infection risk by pathogens, marine organisms have evolved countermeasures to regulate the number of surface-colonizers;alternatively they tolerate settlement and biofilm-formation. Antimicrobial defense mechanisms co-evolved with potentially colonizing microbes. By contrast, non-native animals (neozoa) are confronted with novel microbial colonizers upon colonizing a new habitat, and are expected to be less well protected against surface-colonization. Here we present results of a thorough screening of the epithelial surface of the ctenophore Mnemiopsis leidyi, being non-native in European marine environments, for epithelial bacteria and archaea. Neither light- and electron-microscopic inspection nor PCR-screening for bacterial and archaeal DNA of 134 adult specimens from different collection sites in the Western Baltic revealed any presence of prokaryotes on the surface epithelium of comb jellies in a recently invaded environment. A limited number of bacterial associates became evident from whole-body extracts of both juvenile and adult comb jellies. Their taxonomic diversity, however, was significantly lower in adult than in juvenile specimens, suggesting a maturation of anti-microbial defense upon ontogenetic development. The mechanisms underlying the effective defense of Mnemiopsisagainst microbial colonization, however, remain unknown. Based on our findings, we propose 1) to make use of invasion events as natural space-for-time experiments on how symbiotic interactions change upon environmental change;and 2) to study basal metazoan animals, such as ctenophores, to understand the evolutionary basics of symbiont-host interactions.
基金Zhang Xingliang gratefully acknowledges the financial support by the National Natural Science Foundation of China(Grant NSFC 40402005)the Program for New Century Excellent Talents(NCET)+1 种基金the Program for Changjiang Scholars and Innovative Research Team in Universities(PCSIRT)Joachim Reitner thanks the Deutsche Forschungsgemeinschaft for finacial support(Leibniz award,Re 665/12-1).
文摘The Ediacaran Dickinsonia is well-known for being the only fossil to be assigned to many phyla, ranging from lichens, Cnidaria, Piatyheiminthes, Annelida, and a phylum of its own to a nonmetazoan kingdom. A new specimen from the Ediacaran fine-grained sandstone on the Winter Coast of the White Sea in northern Russia, which has an age of -555 million years ago, preserved convincing internal anatomies of definite animals, comparable with meridionai canals of extant ctenophores （comb jellies）. Additionally, we reconsidered Dickinsonia as a biradiaily symmetrical animal rather than a bilateral one as previously thought. The animal nature of Dickinsonia is, thus, well established and its affinities are most probably allied to ctenophores. This research is not only removing Dickinsonia from Vendobionta, but also bringing the fossil record of ctenophores forward to 20 million years before the Cambrian ＂explosion＂.
