Cassini Spacecraft found older terrains and major fractures on moon Enceladus Course crystalline ice which will degrade over time. Must be < 1000 years old! Organic compounds found in the fractures. Must be heated - required T > 100K (-173˚C) Erupting jets of water observed. Cause of eruptions not known…. Mystery of Enceladus

Lecture 17. Why Do You Need to Construct a Tree for Prokaryotes? Trees as Frameworks

Drawing Trees Trees can be drawn in different ways. Trees are assumed to branch dichotomously (branch in two). Trees show relationships. Branch lengths proportional to the amount of evolutionary change/rate. Relationships are inferred based on the sequence data observed from extant organisms. Phylogenetic tree/Phylogeny shows evolutionary relationships. root

Unrooted tree using 16S ribosomal RNA. Most diversity is in the microbial world. Is an evolutionary framework - can map traits onto the tree Red lineages are thermophilic - all branch around the root so early life lived at high temperatures Independent lineages diverged into low temperatures (blue). Independent lineages able to do photosynthesis (green). Photosynthesis in Bacteria and Eukarya/Eucarya. Multicellular life arose late. Tree of Life

1.Develop well resolved phylogenetic trees = evolutionary framework 2.Map traits (metabolic, morphological, habitat) onto the tree 3.Identify clades (groups that share an ancestor) with traits of interest 4.Compare appearance of traits with the geologic record isotopic signatures, microfossils, etc. 5.Identify age constraints, determine which traits are ancient and derived ….Once you have one or two age constraints, a well-resolved tree will reveal additional age constraints for sister and nested clades! Mapping Traits Onto Trees no aerobic growth aerobic growth equivocal

OctSpA1-106 BH1 BH60 QL3-43 BH81 BH92 EM19 EM3 BH3 QL4-2 BSpN50 Aquifex Thermotoga Deinococcus Thermus 50 changes  -Proteobacteria    Gram Positives (Low G+C) Cyanobacteria Green Sulfurs Gram Positives (High G+C) Green Non-Sulfurs root to Archaea * * * * * * * * * Thermophilic Growth in Bacterial Domain

Euryarchaeota Crenarchaeota mesophilic thermophilic hyperthermophilic ≤2.35 Ga First: hyperthermophilic Thermophilic after 2.35 Ga (no cultured mesophiles) First: hyperthermophilic Thermophilic after 2.35 Ga Mesophilic growth after 2.52 Ga Thermophilic Growth in Archaeal Domain

Just How Ancient is Thermophily? 100˚C 0˚C Last sterilizing asteroid impact time (billion years) temperature hot origin of life cold origin of life prebiotic evolution prebiotic evolution Miller & Lazcano, The Origin of Life- Did It Occur at High Temperatures? J. Mol. Evol., 1995 Origin of life could have occurred at any temperature. Something happened and last common ancestor was a thermophile. -giant meteorite impact -random evolutionary accident -Panspermia -product of an early hot Earth

Reconstructing the Traits of Ancestors Can reconstruct the size of the ancestors of major groups of organisms. Modern cyanobacteria often have large cells - identifying feature in the fossil record. Start seeing large diameter fossils with sheaths at ~ 2.0  m. See fossil akinetes - resting stages typical of the Nostocales at 1.7 Ga. But early cyanobacteria all had cell diameters < 2.0  m, around ~1.0  m.

Can Reconstruct Ecology Early cyanobacteria are unicellular coccoids Filaments arose later Sheath has arisen multiple times independently Motility arose several times Conclusion: traits to make thick microbial mats not ancient.

Can Reconstruct Habitat Earliest Cyanobacteria evolved in a freshwater environment. Several lineages have freshwater ancestors that then colonized marine environments.

Traits that are NOT Old/Ancient in the Archaeal Domain ≤ 2.32 Ga d. NO 3 - reduction can’t reduce NO 3 - can reduce NO 3 - ≤ 2.32 Ga a. SO 4 2- reduction can’t reduce SO 4 2- can reduce SO 4 2- ≤ 2.32 Ga EuryarchaeotaCrenarchaeota

Traits that are NOT Old/Ancient in the Archaeal Domain, cont. EuryarchaeotaCrenarchaeota ≤ 2.32 Ga can’t oxidize S˚ can oxidize S˚ f. S˚ oxidation ≤ 2.32 Ga can’t oxidize sulfides can oxidize sulfides e. Sulfide oxidation ≤ 2.32 Ga

Traits that ARE Old/Ancient in the Archaeal Domain ≤ 2.32 Ga c. S˚ reduction can’t reduce S˚ can reduce S˚ ≤ 2.32 Ga g. H 2 oxidation can’t oxidize H 2 is a methanogen can oxidize H 2 ≤ 2.32 Ga EuryarchaeotaCrenarchaeota

Evolution of Habitat Traits in the Archaeal Domain terrestrial/freshwater marine Habitat ≤ 2.32 Ga Acidophily neutrophile (>pH 6) acidophile (pH 4-6) extreme (pH <4) acidophile ≤ 2.32 Ga EuryarchaeotaCrenarchaeota early: neutrophiles later: extreme acidophiles early: acidophiles later: extreme acidophiles later: neutrophiles early: marine later: terrestrial (freshwater) early: terrestrial later: marine

Summary of Reconstructed Ancient Habitats Euryarchaeota: Temperatures > 80˚C Neutral pH, marine environment Methanogen Crenarchaeota: Temperatures > 80˚C Slightly acidic, terrestrial environment Probably a sulfur reducer

LCA Crenarchaeota (terrestrial solfatara) Euryarchaeota (marine hydrothermal vent) Bacteria (terrestrial near-boiling silica depositing spring) We Have Three Major Microbial Lineages Because They All Trace Back To Three Hydrothermal Ecosystems

Power of Frameworks Not only reconstruct early traits of microorganisms. Can compare with the geologic record to identify when major groups of microbes arose. How did origin of new microbial groups change the chemistry of the early Earth, co-evolution of Earth and life.

Lecture 18. Diversity of Microbial Life. What Do Microbes Need to Survive? Energy and Metabolism. Extremophiles, Photosynthesis, and Chemosynthesis. reading: Chapter 6