© CNRS Photothèque/IGS/AMU The impressive number of genes in new giant viruses dubbed Pandoraviruses shows that they may be a kind of missing link between the other known viruses and eukaryotic cellular microorganisms. GENOMICS STR ANGE GIANT VIRUSES Is there no limit to the complexity of viruses? It would seem not, after the discovery by French researchers1 of two new giant viruses. One of them, dubbed Pandoravirus salinus, was found in 2012 off the coast of Chile. The other virus, Pandoravirus dulcis, was isolated the same year in the sediments of a fresh water pool in Australia. “The name Pandoravirus refers not only to the unusual amphora-like shape of these microorganisms but also to the fact that their genetic makeup is virtually unknown,” explains Jean- Michel Claverie of the Structural and Genomic Information Laboratory (IGS) in Marseille (south-east France). The detailed description of the first two members of the Pandoraviridae family is surprising, to say the least. To begin with, an indepth analysis of their genomes revealed that they have no genes able to make capsid proteins, the geometrical structure that usually forms the coat surrounding viruses. In addition, only 6% of the proteins coded for by the 2,500 genes of Pandoravirus salinus, the more complex of the two new giant viruses, have already been observed in viruses and cellular organisms. Despite their distinctive characteristics, Pandoraviruses are definitely viruses, with their typical absence of ribosomes, energy production and division. For the project coordinator Chantal Abergel, also at the IGS, the unusual nature of these microorganisms suggests that cellular life is more diverse than previously thought: “The fact that Pandoraviruses don't belong to any of the three domains of life—bacteria, eukaryotes and archaea—points to the existence of a fourth domain which may have appeared more than two billion years ago.” 1 Laboratoire Information Génomique et Structurale (CNRS/Aix-Marseille Université); Laboratoire Biologie à Grande Echelle (CEA/Inserm/Université Joseph Fourier Grenoble 1) Science July 2013 © Michael J. Kramer The giant moray eel (Gymnothorax javanicus) hunts at night in the labyrinth of coral reefs, helping to keep the ecosystem in good health. BIODIVERSITY RARE SPECIES PLAY A VALUABLE ROLE While their high extinction rates frequently put them in the spotlight, rare species are paradoxically thought to have a minor influence on ecosystem functioning. Now, for the first time, an international team1 has shown that some of these rare species actually play a unique ecological role, even in the most diverse ecosystems. To reach this conclusion, the scientists first identified the functional traits of 846 species of coral reef fish, 2,979 alpine plant species and 662 tropical trees. “This information, which includes details of their morphology, biological rhythms and diet, is used to determine their ecological functions,” explains David Mouillot of the Ecology of Coastal Marine Systems Research Unit in Montpellier. Within these three large systems, the researchers sought to establish whether the most unusual functions were characteristic of common or rare species. “For all these particularly rich ecosystems, our analysis shows that most unique roles are played by rare species, pointing to their usefulness for the long-term preservation of ecosystem functioning,” Mouillot points out. The example of the giant moray eel is a good illustration. This species feeds on dead and sick animals that it hunts in the tiniest nooks and crannies within the coral reef, thus speeding up nutrient recycling and helping to keep the ecosystem in good health. Because these key functions are essentially performed by rare—and therefore vulnerable— species, they are highly likely to disappear in the event of major environmental change. In this context, implementing nature conservation policies that take account of functional rarity would help preserve the full range of ecosystem functions, while limiting the impact of the disturbances that affect them. 1 Several laboratories and research units bringing together researchers from the CNRS, Université Montpellier 2, Inra, EPHE and IRD contributed to this study. Plos Biology May 2013 11 BEST OF SCIENCE
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