AST 248, Lecture 12 - Stony Brook University · AST 248, Lecture 12 James Lattimer Department of Physics & Astronomy 449 ESS Bldg. Stony Brook University October 19, 2018 The Search

AST 248, Lecture 12

James Lattimer

Department of Physics & Astronomy449 ESS Bldg.

Stony Brook University

October 19, 2018

The Search for Intelligent Life in the [email protected]

James Lattimer AST 248, Lecture 12

Unity of LifeI All lifeforms on Earth have a common system. Examples:

I universal usage of DNA to store genetic informationI the ribosome technique of protein synthesisI proteins serve as enzymes and catalystsI the same 20 amino acids are always used, and only left-handed onesI a universal genetic codeI DNA triplets coding for same amino acidI the use of proteins and lipids to make membranesI the use of the ATP-ADP cycle for chemical energy.

I The subsystems of life are highly interlocked.

Proteins are needed to make enzymes, yet enzymes are needed to makeproteins. Nucleic acids are needed to make proteins, yet proteins areneeded to make nucleic acids.

I The common system is very complex.

It must have been the result of an extended evolution. In evolutionaryterms, it is very far from the original organisms.

I It is possible to construct detailed phylogenetic trees based either onmorphology or molecular (genetic) data.

Conclusion: It must be that all organisms on Earth are descended from a singlecommon ancestor.


Phylogeny and the Nature of the Common AncestorI Evolutionary distance = fractional genetic difference between organisms

I Phylogenetic tree = map of evolutionary diversification

I Three primary groupings or domains:I ArchaeaI BacteriaI Eucarya

I Most deeply diverging lineages in Bacteria and Archaea are thermophiles,suggesting that the common ancestor of all life was also.

I Metabolize compounds rich in H, Sand Fe

I Use anaerobic (sulfur) photosyn-thesis to synthesize carbohydrates

2H2S + CO2 → CH2O + 2S + H2O

and fermentation for respiration(energy release)

2(CH2O)n → nCH4 + nCO2 + energy

I Thrive in oxygen- and sunlight-free environments, likehydrothermal vents

Eric Gaba, NASA Astrobiology Institute


Extremophiles

Organisms (mostly micro-organisms) that require extreme environments forgrowth; “extreme” is a relative and anthropocentric term. Examples:

I Acidophile: optimal growth at pH values less than 3I Alkaliphile: optimal growth at pH values above 10I Endolith: live within rocks, or deep (a mile or more) underground;

antarctic lichensI Halophile: require high salt contentI Hyperthermophile: requires T > 80◦ C, up to 121◦ C; hydrothermal

vents, hot springs, volcanosI Hyper- or Hypo-baric: require high or low pressure; hydrothermal vents,

cold seeps, high-altitude bacteria, bacteria recovered from lunar SurveyorIII camera

I Lithoautotrophes: live in igneous rocks. utilize no organic products ofphotosynthesis or sunlight, need only CO2, H2O and H2 to survive

I Oligotrophe: optimal growth in limited nutrient conditionsI Psychrophile: optimimum T < 15◦ C, maximum of 20◦ CI Toxitolerant: can withstand high levels of benzene, radiation, etc.

Radio-resistant insects and bacteria, organisms living within metals orliquid hydrocarbons.

I Xerotolerant: capable of growth at low water activity, e.g., halophile orendolith; revived bacteria from stomachs of frozen mammoths and fromfossilized amber, plant seeds from tombs.


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Yellowstone hot springsWebshots channel: outdoors


Extremophiles

I Oyster’s early ancestors had brains, but discarded them throughevolution.

I 1/4 of world’s copper mining is done by microbes.

I Urban bio-mining could remediated brownfield sites and reducerecycling.

I The history of extremophile research is largely the history of foodpreservation. It’s a way to go beyond the limits of life by chemicallyor physically treating food so that nothing grows on it (hightemperatures, drying, pickling, salting, smoking, refrigeration, etc.)

I Many extremophiles have been discovered by studying foods thatspoil even when stored in hostile conditions. (Halophiles found whileinvestigating salt fish spoilage. Deinococcus radiodurans discoveredusing γ-radiation to sterilise canned food.)




Adaptations to ExtremesSpores Reproductive structures that permit dispersal and survival for

extended periods in unfavorable conditions. Form part of lifecycles of many plants, algae, fungi and single-celled eukaryotes.

Endospores A dormant, tough, non-reproductive structure produced bysome bacteria and archaea, whose primary purpose is to ensuresurvival through periods of environmental stress. The parentcell copies its DNA and encloses the copy into a little cell(daughter) that is then surrounded by the material used tomake cell walls, peptidoglycan. Another external sheath ofproteins protects it. Harsh conditionswither or blast away the surroundingparent cell, leaving the endospore.They are resistant to

I ultraviolet and gamma radiationI desiccation or extreme drynessI lysozyme, an enzyme that damages

bacterial cell wallsI temperatureI starvationI chemical toxins

Anthrax, botulism, tetanusExospores These form outside by growing or

budding out from one end of a cell.Cysts Thick-walled structures that protect

bacteria from harm, not as durable.


Technological ApplicationsSource Application

Psychrophilesalkaline phosphatase molecular biology

proteaeses, lipases, cellulases, amylases detergentslipases, proteases cheese manufacture, dairy products

polyunsaturated fatty acids food additives, dietary supplementsvarios enzymes modifying flavorsb-galactosidase lactose hydrolysis in milk products

ice-nucleating proteins artificial snow, ice creamice-minus microorganisms frost protectants for sensitive plants

various enzymes (e.g. dehydrogenases) biotransformationvarious enzymes (e.g. oxidases) bioremediation, environmental biosensors

methanogens methane productionHyperthermophiles

DNA polymerases DNA amplification by PCRproteases, amylases, a-glucosidase baking, brewing

pullulanase and xylose/glucose isomerases production from keratinalcohol dehydrogenase chemical synthesis

xylanases paper bleachinglenthionin pharmaceutical

s-layer proteins and lipids molecular sievesoil-degrading microorganisms surfactants for oil recovery

sulfur oxidizing microorganisms bioleaching, coal waste gas desulfurizationhyperthermophilic consortia waste treatment and methane production


Implications

I Extreme environments on present-day Earth were commonplace onthe early Earth.

I For the first billion or more years after life arose on the Earth, onlyextremophiles could have survived.

I Total mass of extremophiles may well exceed those of ordinarylifeforms today.

I Humans 100 MTI Domesticated animals 700 MTI Crops 2 BTI Bacteria 2 BTI Fish 1–2 BTI Archae 2+ BT

I Phylogenetic arguments reinforce the notion that extremophileorganisms are the most primitive; hence they did not adapt to theirpresent extreme environments, rather, ordinary life adapted orevolved from them.

I The fact that extremophiles can survive such a broad range ofconditions suggests life may be possible outside of the “habitablezone” commonly envisioned.


Earliest Geologic Records of Life

I 4.28 Gyrs (Huvvuagittuq Belt, Quebec) microfossils in hydrothermalvent precipitates

I 4.1 Gyrs (Jack Hills, Western Australia) chemofossils in flecks ofgraphite in zircon crystals

I 3.85 Gyrs (Akilia Island, Greenland) chemofossils, possiblystromatolites

I 3.48 Gyrs (North Pole and Onverwacht, Australia) bacteria-likemicrofossils in geyserite of apparently fossilized cells of filamentousorganisms

I 3.48 Gyrs (Western Australia) oldest fossilized remnants ofsingle-celled cyanobacterial microbial mats (stromatolites)

I 3.465 Gyrs (Australian Apex) microorganisms, earliest directevidence

I 3.2 Gyrs (Fig Tree, S. Africa)I 2.6–2.7 Gyrs (Eastern Transvaal, S. Africa) fossilized microbial mats

(stromatolites); oldest evidence of life on land, requiring ozone layerand O2 in atmosphere.


Carbon Isotopes

Isotopic evidence (chemofossils) may be more reliable indicators thanshape (microfossils), but are still controversial.

There are non-living ways of increasing the C12/C13 ratio. These include,for example, some rare types of meteorites have higher ratios thannormal, and the so-called Fischer-Tropsch reactions, in which carbon,oxygen, and hydrogen react with a catalyst like iron to form methane andother hydrocarbons. Such reactions probably occurred near hydrothermalvents in the Hadean Eon.

C12/C13 = 120 in fossilizedmaterial, same as in present-dayliving matter.

C12/C13 = 99 in non-livingterrestrial matter.

Jack Hills zircon crystal


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AST 248, Lecture 12 - Stony Brook University · AST 248, Lecture 12 James Lattimer Department of Physics & Astronomy 449 ESS Bldg. Stony Brook University October 19, 2018 The Search