LECTURE
1O &
The Earth is about 4.5 billion years old. Microorganisms have been around for about 4 billion years. The early Earth was anoxic and much hotter.
MICROBIAL EVOLUTION Classification
Fig. 10.14 Stromatolites
Fossilized, photosynthetic, microbial mats
The evidence suggests that biologically important molecules could be formed when gaseous mixtures like the primitive Earth are irradiated or shocked.
The earliest organisms probably did not have any DNA. They consisted of RNA and just a few, if any proteins. When self-replicating RNA molecules became enclosed in membranes, they became the first cellular life forms. Soon, proteins become main cellular enzymes.
Evolution of Life - a Time Scale
Using DNA as the genome likely resulted from the need to store genetic information in a more stable form.
What is the origin of eukaryotes? Many theories e.g.: 1) Archaea-like cells evolved a nucleus, endomembranes, and cytosketeton. 2) Endosymbiotic theory: Archaea like cell engulfed a Gram - bacterium = mitochondrion or a cyanobacterium = chloroplast See next slide and read Perspective 3.1 on page 76
The Evolution of Endosymbiosis
Classifying Microorganisms
The grouping of organisms according to distinguishing characteristics that they share.
Why is taxonomy and systemmatics important? 1) Allows information to be organized so it can be easily accessed by all in the scientific community. 2) By knowing properties and characteristics, we can make predictions about related organisms. (model organisms) 3) Allows for a common language. Enforces strict rules. 4) Essential to accurately identify organisms.
History of attempts to classify microbes..
A little after the time of Leeuwenhoek (lec. 2), Linnaeus tried to classify all living things 1759, named all known organisms using the binomial system (Genus species). divided the world into Animal, Vegetable and Mineral Not much was known about microbes at that time so Linnaeus gave up in frustration and put all microscopic life into one genus, Chaos!
Whittaker (1969) and others 5 kingdom system: Plants, Animals, Fungi, Protists and Bacteria 3 main modes of nutrition: photosynthesis, adsorption, and ingestion show foot tree (next slide) This tree of life has been widely accepted but it is not phylogenetically correct.
What is monophyly?
Not monophyletic
Monophyletic group
Archaea??
Not a monophyletic group
Fig. 10.1. The 3-Domain system used in modern biology
An aside on taxonomic ranks and the binomial system.
Table 10.01
The Binomial System
Systematics
The science of characterizing and organizing living things, hopefully in a phylogenetic (evolutionarily historical) way See Figure 10.18
Bacillus anthracis
Proteus vulgaris
B. Subtilis
Genus species names should be in italics or underlined E. coli or E. coli
Fig. 10.18. Example of a phylogenetic tree. Nodes are ancesteral branch points or points of common ancestors.
What are characters?
Fig. 10.18
The information used to compare organisms.. morphological characters metabolic characters molecular characters
G+C content of DNA - useful for grouping Bacteria
Molecular Systematics
Less ambiguous esp. for microbes
Fig. 10.16
G + C content may seem like a crude measure, but its proven to be quite valuable for microbial taxonomy. But, it still doesnt tell you anything about the sequence of the organisms DNA.
Molecular characters - II. DNA-DNA hybridization
Fig. 10.17. DNA-DNA hybriization
Fig. 10.17
Modern systematics is based on direct examination of the blue prints of life i.e. DNA and RNA sequences.. The most useful sequences for classifying all forms of life are ribosomal RNA because they are:
1)found in all forms of life 2)change slowly (over evolutionary time)
Figure 10.9
Molecular characters - III. Nucleic Acid Sequencing SSU Ribosomal RNA
Fig. 10.1
Bacteria
Archaea
Eukaryote
