Class2 - Class #2 The Nature of the Microbial World...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Class #2 The Nature of the Microbial World Prokaryotes (Bacteria & Archaea) Eukaryotes .. .. The Nature of the Microbial World The diversity of microbes is enormous! .. Diversity of Life The greatest contribution to the Earth's biodiversity is made by... MICROORGANISMS Bacteria Archaea Fungi Protozoa Algae ACELLULAR MICROORGANISMS Viruses Viroids Prions DNA or RNA, + protein RNA Protein HIV, T4 phage Potato spindle tuber BSE (mad cow disease) How do we find order in the microbial world? The diversity of microbes is enormous! .. What defines life? Halmarks of life Information Processing Mechanical Functions How do we find order in the microbial world? Traditionally Taxonomy "Natural Order" or Evolutionary History Phylogeny Taxonomy classification uses established rules nomenclature binomial, genus + species e.g., Escherichia coli or E. coli identification assigning a name to an unknown organism to place it properly in the classification system --traditionally taxonomy has been based on readily observable characteristics, e.g. morphology, physiology; now taxonomy also relies on genomic traits and phylogeny How do we find order in the microbial world? Phylogeny Ordering of organisms based on evolutionary relationships "Natural Order" or Evolutionary History Phylogenetic "Trees" (Microbial "Family Trees") Darwin's Tree Microbial Family Tree PROBLEMS! How do we establish evolutionary relationships among microbes without an extensive fossil record? molecular phylogeny Molecular Phylogeny Concept developed by: Emile Zuckerkandl & Linus Pauling (1965) "Evolutionary distances between species can be measured by differences in the nucleic acid or amino acid sequence of homologous molecules." Molecule of choice: Ribosomal RNAs (rRNAs) Molecular Phylogeny Molecule of choice: ribosomal RNAs (rRNAs) Important features: 1) universally distributed 2) constant function 3) structure conserved 4) high information content 16S rRNA [Small Subunit (SSU) ribosomal RNA] -- molecule of choice for phylogenetic studies Molecular Phylogeny Methods: Sequence of 16S rRNA gene (16S rDNA) is obtained 16S rDNA sequences from different microbes are aligned & compared; differences are counted Corrections are made based on statistical considerations; various programs are used to order the sequences and present them as trees with more divergent sequences further apart Universal Tree of Life Universal Tree of Life Microbes! Universal Tree of Life Prokaryotes Universal Tree of Life Eukaryotes Universal Tree of Life Endosymbiont Hypothesis Symbiogenesis Revised Tree of Life showing lateral gene transfer W. F. Doolittle Evolutionary relationships (phylogeny) among all organisms have been determined by: sequencing membrane lipids comparing mitochondria sequencing 16S ribosomal RNA genes comparing chloroplasts ...
View Full Document

This note was uploaded on 04/18/2008 for the course MICROBIO 310 taught by Professor Dolan during the Spring '08 term at Univ. of Massachusetts Med. School.

Ask a homework question - tutors are online