Asgard archaea the closest prokaryotic relatives of eukaryotes

Abstract

Asgard arheje nastanjuju raznolika staništa najčešće anoksičnih uvjeta kao što su hidrotermalni izvori te sedimentni morski i slatkovodni ok oliši. U takvim okolišnim uvjetima česte su mikrobne interakcije koje su uočene i kod ove skupine, ali još nisu detaljnije istražene. Metabolizam Asgard arheja veoma je raznolik. Određena koljena sposobna su razgrađivati masne i druge organske kiseline, pr oteine i ugljikohidrate. Ovi organizmi često su fermentativni te tako ovisno o koljenu produciraju acetat, laktat ili etanol. Također, jednim od dvaju tipova Wood Ljungdahl (WL) puta reduciraju CO 2, dok su u nekih koljena zabilježena oba tipa. Posljednje o tkriveno koljeno Helarchaeota specifično je jer kodira za metil CoM enzime slične reduktazi (Mcr) te stoga ima potencijal za oksidaciju uglji kohidrata. U nekih koljena nađen je kompletan set gena za protein RuBisCo tip III i IV te su identificirani novi pi gmenti koje sadrže ove arheje heliorodopsin i schizorodopsin. Mogu sudjelovati i u kruženju dušika i sumpora. Većina ih je obligatno anaerobna, dok linija Heimdallarchei a ima potencijal fakultativno aerobnog metabolizma. U genomu Asgard arheja nađeno je mnogo proteina ESP s za koje se smatralo da postoje samo u eukariota. Najznačajniji su oni za citoskelet, primjerice homolozi aktina, tubulina i profilina te oni za membranski transportni sustav, primjerice male GTP aze i komponente vezikularnih omotača. N apredak u sekvenciranju molekule DNA te razvitak metagenomskih metoda pružaju podatke o novim arhealnim linijama. Novije filogenetske analize smještaju euk ariote unutar Asgard arheja, s koljenom Heimdallarchaeota kao najbližim eukariotskim srodnikom. Sve n avedeno pomaže razumijevanju eukariogeneze i postavljanju novih modela ovog ključnog evolucijskog događaja.Asgard archaea have been found in a diverse range of habitats, primarily in anoxic conditions, including hydrothermal vents, marine an d freshwater sediments. These conditions support microbial interactions that are also observed in Asgard superphylum but so far are unexplained. Metabolism of Asgard archeae is very versatile. Some phyla are capable of degradation of fatty and other organi c acids, proteins and carbohydrates. These organisms often ferment so that they can produce acetate, lactate or ethanol. Moreover, they reduce CO 2 via one of two Wood Ljungdahl (WL) pathways, while some use both of the m. The latest discovered phylum Helarc haeota has specific metabolism because it encodes for methyl CoM reductase like enzymes (Mcr) so it has potential for hydrocarbon oxidation. Some phyla were found to harbor complete set of genes for RuBisCo types III and IV. Recently, new Asgard archea pig ments are identified heliorhodopsin and schizorhodopsin. Some of the archea are also involved in nitrogen and sulfur cycling. Most of them are obligately anaerobic, while archaeal lineage Heimdallarchaeia has potentially facultative aerobic metabolism. A sgard archaea genome encoded for numerous eukaryotic signature proteins (ESPs) that were previously considered to be eukaryotic specific. The most significant ESPs are for cytoskeleton, such as actin, tubulin a nd profilin homologues and ESPs for membrane t rafficking system such as small GTPases and vesicle coat components. Developed DNA sequencing technologies and me tagenomic approaches provide us datasets about new archaeal lineages. New phylogenetic analysis place eukaryotes within the Asgard superphylum, more closely related to the phyllum Heimdalla rchaeota. All these discoveries help in understanding of eukaryogenesis and proposing new models for this key evolutionary event