Astrobiology Science Conference 2015 (2015) 7328.pdf AN ESTIMATE OF THE ELEMENTAL COMPOSITION OF LUCA. Aditya Chopra1 and Charles H. Lineweaver1, 1Planetary Science Institute, Research School of Earth Sciences and Research School of Astronomy and Astrophysics, Australian National University, [email protected], [email protected] A number of genomic and proteomic features of composition of life, we attempt to account for life on Earth, like the 16S ribosomal RNA gene, have differences in composition between species and other been highly conserved over billions of years. Genetic phylogenetic taxa (Fig. 2) by weighting datasets such and proteomic conservation translates to conservation that the result represents the root of prokaryotic life of metabolic pathways across taxa. It follows that the (LUCA). Variations in composition between data sets stoichiometry of the elements that make up some of that can be attributed to different growth stages or the biomolecules will be conserved. By extension, the environmental factors are used as estimates of the elemental make up of the whole organism is a uncertainty associated with the average abundances for relatively conserved feature of life on Earth [1,2]. each taxa. We describe how average bulk elemental Euryarchaeota 1a Methanococci, Methanobacteria, Methanopyri 7 Euryarchaeota 1b abundances in extant life can yield an indirect estimate 6 Thermoplasmata, Methanomicrobia, Halobacteria, Archaeoglobi Euryarchaeota 2 4 Thermococci of relative abundances of elements in the Last Crenarchaeota Sulfolobus, Thermoproteus ? Thaumarchaeota Universal Common Ancestor (LUCA). The results Cenarchaeum ? Korarchaeota ARMAN could give us important hints about the stoichiometry ? 2 Archaeal Richmond Mine Acidophilic Nanoorganisms Nanoarchaeota of the environment where LUCA existed and perhaps Archaea Terrabacteria clues to the processes involved in the origin and early Actinobacteria, Deinococcus-Thermus, 1 Cyanobacteria, Life Chloroflexi, 9 evolution of life [3]. Fermicutes Hydrobacteria Spirochaetes, Bacteroidetes, Epsilonproteobacteria Bacteria Planctomycetes, Chlorobi, We conducted a meta-analysis of historical and 8 Chlamydiae, Acidobacteria Deltaproteobacteria, Alphaproteobacteria 5 Betaproteobacteria, Gammaproteobacteria 3 recent studies which examined the elemental Fusobacteria Aquificae abundances in various taxa; for example, those Thermotogae t0 presented in [4,5]. Our compilation samples 4.5674.4 4.2 4.03.8 3.6 3.43.2 3.0 0 Heavy Bombardment Origin Moon eukaryotic, bacterial and archaeal taxa across the Present day of Solar forming Billion years ago extant tree of life. Based on the elemental abundances system impact therein and the phylogenetic relationship between the Fig. 2: The earliest divergences in the phylogenetic taxa, we derived our best estimate for the elemental tree of life used for weighting elemental abundances composition of LUCA (Fig. 1). by phylogeny. Overlapping relative uncertainties in emergence time of taxa are indicated by grey bars [7]. H Li B N F Na Al P Cl K Sc V Mn Co Cu Ga As Br Rb Y Nb Tc Rh Ag In Sb I Cs La Pr Pm Eu Tb Ho Tm Lu Ta Re Ir Au Tl Bi At Fr Ac Pa He Be C O Ne Mg Si S Ar Ca Ti Cr Fe Ni Zn Ge Se Kr Sr Zr Mo Ru Pd Cd Sn Te Xe Ba Ce Nd Sm Gd Dy Er Yb Hf W Os Pt Hg Pb Po Rn Ra Th U 103 H C 2 10 O N Cl K Ca 10 Si Over the past ~4 billion years, the habitats Na S Mg 1 Al P Fe Rb occupied by life forms have changed in composition as B Zn −1 10 Mn Br previously inhabited environments became colonized. −2 V Sr Pb F Ti 10 Cu Cr Ni −3 Zr The extent of conservation in the elemental 10 Co Cd Sn Te I Ba −4 As Mo 10 Ga Ag Li Se Y Nb U composition since LUCA, and how elemental Hg W −5 Nd Yb = 1 10 Sb Ce Ge DyHo P La abundances in life change in response to Sc Cs −6 Be 10 SmEu Ta In Tb LuHf Abundance (number of atoms) −7 Tl Bi Th environmental changes provide a means to study both 10 Au 10−8 the origin and evolution of life [8]. 10−9 −10 10 Pr Gd Er 10−11 References: [1] Williams R.J.P. & da Silva J.F. Tm 10−12 (2005) The Chemistry of Evolution, Elsevier [2] Elser 10−13 H Li B N F Na Al P Cl K Sc V Mn Co Cu Ga As Br Rb Y Nb Tc Rh Ag In Sb I Cs La Pr Pm Eu Tb Ho Tm Lu Ta Re Ir Au Tl Bi At Fr Ac Pa He Be C O Ne Mg Si S Ar Ca Ti Cr Fe Ni Zn Ge Se Kr Sr Zr Mo Ru Pd Cd Sn Te Xe Ba Ce Nd Sm Gd Dy Er Yb Hf W Os Pt Hg Pb Po Rn Ra Th U J.J. (2003) Biological stoichiometry, IJA, 2 , 185-193 [3] Chopra A. et al. (2010). In Proceedings from 9th Fig. 1: The bulk elemental composition of LUCA Australian. Space Science Conf. [4] Bowen H.J.M. estimated from abundances in extant taxa. (1979) Environmental chemistry of the elements, AP. [5] Li Y.-H. (2000) A Compendium of Geochemistry, Previous work dealt mostly with single species or PUP. [6] Chopra A. & Lineweaver C.H. (2009). In was limited in the breadth of elements considered [6]. Proceedings from 8th Australian Space Science Conf. We used abundances for almost all of the biologically [7] Lineweaver, C.H. & Chopra, A. (2012) What can relevant elements, including the major elements (H, O, Life on Earth Tell Us about Life in the Universe? In C, N, P, S) and minor elements (e.g. Na, K, Mg, Ca, Seckbach J. (Ed.), Genesis, 799-815 [8] Chopra A. & Fe, Cu, Zn). In establishing an average elemental Lineweaver C.H. (2015, in prep.) .