- Thijs J.G. Ettema (2)
- Jon Jerlström-Hultqvist (1)
- Anna Kokla (1)
- Jonathan Lombard (1)
- A.C. Smaal (1)
- Anja Spang (1)
- Staffan Svärd (1)
- Courtney W. Stairs (2)
- Ásgeir Ástvaldsson (1)
Proposal of the reverse flow model for the origin of the eukaryotic cell based on comparative analyses of Asgard archaeal metabolism
Spang, Anja ; Stairs, Courtney W. ; Dombrowski, Nina ; Eme, Laura ; Lombard, Jonathan ; Caceres, Eva F. ; Greening, Chris ; Baker, Brett J. ; Ettema, Thijs J.G. - \ 2019
Nature Microbiology 4 (2019). - ISSN 2058-5276 - p. 1138 - 1148.
The origin of eukaryotes represents an unresolved puzzle in evolutionary biology. Current research suggests that eukaryotes evolved from a merger between a host of archaeal descent and an alphaproteobacterial endosymbiont. The discovery of the Asgard archaea, a proposed archaeal superphylum that includes Lokiarchaeota, Thorarchaeota, Odinarchaeota and Heimdallarchaeota suggested to comprise the closest archaeal relatives of eukaryotes, has helped to elucidate the identity of the putative archaeal host. Whereas Lokiarchaeota are assumed to employ a hydrogen-dependent metabolism, little is known about the metabolic potential of other members of the Asgard superphylum. We infer the central metabolic pathways of Asgard archaea using comparative genomics and phylogenetics to be able to refine current models for the origin of eukaryotes. Our analyses indicate that Thorarchaeota and Lokiarchaeota encode proteins necessary for carbon fixation via the Wood–Ljungdahl pathway and for obtaining reducing equivalents from organic substrates. By contrast, Heimdallarchaeum LC2 and LC3 genomes encode enzymes potentially enabling the oxidation of organic substrates using nitrate or oxygen as electron acceptors. The gene repertoire of Heimdallarchaeum AB125 and Odinarchaeum indicates that these organisms can ferment organic substrates and conserve energy by coupling ferredoxin reoxidation to respiratory proton reduction. Altogether, our genome analyses suggest that Asgard representatives are primarily organoheterotrophs with variable capacity for hydrogen consumption and production. On this basis, we propose the ‘reverse flow model’, an updated symbiogenetic model for the origin of eukaryotes that involves electron or hydrogen flow from an organoheterotrophic archaeal host to a bacterial symbiont.
Oxygen induces the expression of invasion and stress response genes in the anaerobic salmon parasite Spironucleus salmonicida
Stairs, Courtney W. ; Kokla, Anna ; Ástvaldsson, Ásgeir ; Jerlström-Hultqvist, Jon ; Svärd, Staffan ; Ettema, Thijs J.G. - \ 2019
BMC Biology 17 (2019)1. - ISSN 1741-7007 - 1 p.
Anaerobiosis - Diplomonads - Giardia - Lateral gene transfer - Oxygen stress - Parasitology - Protist - RNAseq - Spironucleosis - Spironucleus
BACKGROUND: Spironucleus salmonicida is an anaerobic parasite that can cause systemic infections in Atlantic salmon. Unlike other diplomonad parasites, such as the human pathogen Giardia intestinalis, Spironucleus species can infiltrate the blood stream of their hosts eventually colonizing organs, skin and gills. How this presumed anaerobe can persist and invade oxygenated tissues, despite having a strictly anaerobic metabolism, remains elusive. RESULTS: To investigate how S. salmonicida response to oxygen stress, we performed RNAseq transcriptomic analyses of cells grown in the presence of oxygen or antioxidant-free medium. We found that over 20% of the transcriptome is differentially regulated in oxygen (1705 genes) and antioxidant-depleted (2280 genes) conditions. These differentially regulated transcripts encode proteins related to anaerobic metabolism, cysteine and Fe-S cluster biosynthesis, as well as a large number of proteins of unknown function. S. salmonicida does not encode genes involved in the classical elements of oxygen metabolism (e.g., catalases, superoxide dismutase, glutathione biosynthesis, oxidative phosphorylation). Instead, we found that genes encoding bacterial-like oxidoreductases were upregulated in response to oxygen stress. Phylogenetic analysis revealed some of these oxygen-responsive genes (e.g., nadh oxidase, rubrerythrin, superoxide reductase) are rare in eukaryotes and likely derived from lateral gene transfer (LGT) events into diplomonads from prokaryotes. Unexpectedly, we observed that many host evasion- and invasion-related genes were also upregulated under oxidative stress suggesting that oxygen might be an important signal for pathogenesis. CONCLUSION: While oxygen is toxic for related organisms, such as G. intestinalis, we find that oxygen is likely a gene induction signal for host invasion- and evasion-related pathways in S. salmonicida. These data provide the first molecular evidence for how S. salmonicida could tolerate oxic host environments and demonstrate how LGT can have a profound impact on the biology of anaerobic parasites.
Voorraad platte Zeeuwse oester staat er wonderwel bij: Rolls Royce onder de oesters lijkt Bonamia-ziekte te boven (interview met Aad Smaal)
Smaal, A.C. - \ 2012
Visserijnieuws 32 (2012)37. - ISSN 1380-5061 - p. 1 - 1.
european eels - palingen - ladders - trap - vismigratie - eels - stairs - fish migration
Voorzitter Alex Koelewijn van de Stichting Duurzame Palingsector Nederland presenteerde vorige week bij de start van het project ‘Paling over de dijk’ een aalladder. Via zulke kunststoftegels zou paling zelf ook goed stuwen en dijklichamen kunnen passeren. ,,Aal kan wel klimmen, maar niet springen. Het gros van de vistrappen helpt paling dus onvoldoende’’, aldus Koelewijn.