Microbio Lec 13 EXAM 3

Origin of Earth + Cellular Life

Origin of Earth

• is ~4.5 billion yrs old

• water appeared ~4.3billion

• cellular life MAY have originated @ hydrothermal systems on ocean floor

  • abundant supply of energy (H₂ and H_sS) prob found around these sites

  • geochemistry support abiotic prod of molecules req. for life (amino acids, lipids, sugars, + nucleotides)

Origin of Cellular Life

• life may have begun w/ RNA

  • RNA essential cofactors +molecules

  • can bind to small molecules

  • has catalytic activity → may have catalyzed its own synthesis

  • earliest virus may have evolved from RNA genome cell-like structures

• PROTEINS EVENTUALLY REPLACED RNA as catalysts

  • DNA became genome + template

  • earliest cells prob had DNA, RNA, protein, + membrane sys. for energy conservation

  • LUCA existed ~3.8-3.7 billion years ago then bacteria + archaea diverged

Metabolic Diversification: Consequences of Earth’s biosphere

Metabolism of primitive cells was EXCLUSIVIELY anaerobic

• obtained carbon from CO₂ (autotrophy) → eventually evolved ability to use N₂

• obtained energy from H₂; early chemolithotrophic metabolism would’ve supported prod. of large amnts of organic compounds

• phototrophs used energy from SUN to oxidize H₂S, H, + H₂O to syn. complex organic molecules

  • 1st phototroph were anoxygenic (EARTH was prev. anoxic)

• Cyanobacteria → O2 prod → oxygenic phototrophs evolved

  • phototrophic bacteria (cyanobacteria + chloroflexus) from modern stromatolites (ancient stromatolites contain fossils similar to modern phototrophic bacteria)

Photosynthesis + Oxidation of Earth

~2.5-3.3 billion years ago cyanobacteria evolved a photosystem that could use H₂O instead of H₂S making O₂

• allowed evolution life to exploit energy from O₂ respiration

  • respiring O₂ was energetically advantageous

• O₂ reacted spontaneously w/ reducing iron → formed iron oxide instead of accumulating

• GREAT OXIDATION EVENT → ~2.4 billion yrs ago

  • laminated sedimentary rocks → banded iron formations from precipitated iron oxide

  • atmosphere gradually became OXIC

• made ozone shield/ layer(O₃)

  • earth’s surface previously inhospitable

  • shield allowed organisms to expand range over surface

Living Fossils: DNA Records the History of Life

Phylogeny → evolutionary history of related DNA sequences

CARL WOESE → tree of life

• CREATED universal tree of life (PHYLOGENETIC TREE) based on nucleotide seq. similarity in ribosomal RNA (rRNA)

• established 3 domain of life (BAE)

• root rep. when all life shared LUCA (was likely prokaryotic w/ DNA genome + ability to transcribe + translate proteins)

• EX: 60+ genes shared by nearly all cells → must’ve been present in LUCA

• Divergence of Eukarya from archaea resulted in membrane enclosed nucleus → organelles gave rise to eukaryotic cell structures

Endosymbiosis Hypothesis

hypothesis for origins of Eukaryotic cells

• proposed a series of engulfment events where host cells engulf bacteria

• Focus on sequential organelle acquisition (metabolic dependency)

• Contend that mitochondria arose from stable incorporation of an aerobic respiring bacterium in the cytoplasm Of early eukaryotic cells

• Chloroplasts arose from incorporation of Cyanobacterium-like Cell into cytoplasm of Eukaryotic cell leading to Eukaryotic photosynthesis

• Oxygen spurred evolution of organelle containing eukaryotic organisms

• Genome structure of mitochondria and chloroplast supports endosymbiosis hypothesis

Formation of Eukaryotic Cell

Is chimeric and made of genes from both bacteria and archaea

Hypothesized Explaination:

• 1) Serial Endosymbiosis hypothesis → 1st began as nucleus-bearing lining that split from archaea then later acquired mitochondria and chloroplast from endosymbiosis

  • occurred when line engulfed a bacterial cell that survived and replicated

• 2) Symbiogenisis Hypothesis → arose from symbiotic relationship between archaea and bacteria; bacteria partner was engulfed to form mitochondria

  • Hydrogen hypothesis → arose from H2 prod. Bacterium and H2 consuming Achaea

  • Genes for lipid biosynthesis were transferred from bacterial symbiont to archaeal host

Phylogenetic Tree

Composition and construction that depicts evolutionary history and resembled family tree

• composed of nodes and branches

• Branch tips → species that exist today

• Nodes → ancestor diverged into 2 lineages

• Branch length → # of changes that have occurred along the branch

Taxonomic Methods in Systematics

Gene Sequence Analyses

• *****SSU rRNA is universal****

  • functionally constant

  • Highly conserve (meaning slow evolution)

  • Adequate length (not too long and short, making it good for study)

• SSU rRNA not always useful for distinguishing closely related species

• Other highly conservative genes (EX: recA and gyrB) useful for distinguishing at species level

MLST (multilocus Sequence typing)

• Another way to differentiate different organism that have similar genes

• Method in which several different "housekeeping genes" from an organism are sequenced

  • housekeeping genes = essential functioning genes

Genome Fingerprinting

• Ribotyping → method of identifying microbes from analyzing DNA fragments generated from restriction enzyme digestion of gene encoding SSU rRNA generating a pattern called a ribotype

  • used in bacterial identification in clinical diagnostics and microbial analyses of food, water, and beverages

Phenotypic Analysis

• EX: fatty acid analysis

  • Types and proportions of fatty acids in cytoplasmic membrane lipids

  • FAME (fatty acid methyl ester)

    • Widespread use in clinical, public health, and food/water inspection laboratories to identify pathogens

    • Relies on variation in composition of fatty acids in membrane lipids for specific prokaryotic groups

Classification and Nomenclature

Taxonomy → how organisms are classified and named

Classification → organization of organism into progressive more inclusive groups on the basis of either phenotypic similarity or evolutionary relationship

Species → 1 to several strains

Genus (genera) → group of several species

How Are Species Named

Prokaryotes given descriptive genus using binomial system of nomenclature used throughout biology

• Names for new species and higher groups of prokaryotes regulated by International Code of Nomenclature of Bacteria

• New isolates are examined to see if it’s sufficiently different to be a new taxon.

  • Requires detailed description of characteristics/traits and proposed name

  • At least 2 international culture collections

• IF organism is well-characterized BUT NOT yet cultured, provisional taxonomic name with Candidatus can be used

Bergey’s Manual of Systematic Bacteriology most widely accepted classification of prokayotes

• no official classification released yet

Culture Collections

National microbial culture collections are an important foundation.

• catalog and store

• protect diversity

• store viable cultures (frozen or free-dried)

• act as repositories for type strains