Transcript Lecture 1 Thursday Jan. 4, 2001

BIOLOGY 304F
EVOLUTION OF PLANTS
Fall 2008
Lecture 4
Thursday September 25, 2008
Chapter 13, Prokaryotes and Viruses
Microbiology in One Lecture
• Whole courses at UWO on prokaryotes and viruses, or
even groups of them or their physiology, ecology or
impacts (e.g., microbial ecology, human diseases) – we
will cover them today as part of the evolution leading
to plants.
• Text covers them well at an appropriate level in just 25
pp. Be sure to know the “Checkpoints” (1st page) and
“Summary” plus “Selected Key Terms” (last 3 pages).
Some statistics:
• 3000 or so described species of prokaryotes (all
treated under the Bacterial Code)
• In the open ocean, make up 90% total biomass
• On land, there may be in the order of 1-10 x 109
cells per gram dry weight of soil, and these may
represent 4000 or more “species” based on DNA
re-association experiments.
• 1 x 1010 to 1012 cells per gram in your guts!
Bacterial Origins
• Oldest known fossils are 3.5 BYA, suspected to
be ancient cyanobacteria, but possibly not; first
forms were almost undoubtedly heterotrophs,
not autotrophs.
• Arguments now about whether first cells
developed in super-hot environments such as
hot springs or deep-sea thermal vents at 90100+ C, or in more moderate conditions at the
edges of seas or lakes. Archaea are probably not
the oldest group, despite their name.
Bacterial Evolution
• Review tree of life and a Woese tree
Bacterial Structure and Parts
• Review bacterial cell structure, and cell walls of
Gram+ and G• Not all bacteria have flagella (vs. subheading p.
284)
• Fimbriae and sex pili, endospores
Ancestral
Cyanobacterium
Ancestral Purple Non-Sulfur Bacterium
Bacterial Shapes and Terms
• Rods, cocci, spirilla and filamentous
[many, but by no means all, human
pathogens are cocci, whereas nearly all
plant paths are G- rods]
• aerobes and anaerobes
• thermophiles, psychrophiles, halophiles;
extreme, facultative and obligate
Bacteria are Not all Single-Celled
• There are colonial bacteria in a true sense –
cooperation among individuals in a colony; and
many “single-celled” forms have colonial
communication such as quorum-sensing and
chemotaxis.
Methods of Genetic
Recombination in Bacteria
• Conjugation via pilus (pl. pili)
• transformation [DNA outside of cells is
frequently stabilized for years to centuries
by adsorption to soil colloids or organic
compounds; however, this also is the basis
for “cloning”]
• transduction [also used as a technique in
cloning to get desired DNA into a cell]
Selected Groups of Bacteria,
and their Importance*
1. Cyanobacteria
Fall within G+ group, have chlorophyll a,
carotenoids, and two phycobilins:
phycocyanin and phycoerythrin (bluish and
reddish); heterocysts (N2-fixation) and
akinetes (resistant “spores”); possible
endosymbiont of red algal chloroplasts
Bacterial Groups II
2. Actinomycetes
Filamentous Gram+; abundant in soil;
odour of fresh soil = geosmin; some cause
plant diseases, many very important in
producing antibiotics, including antassociates; Frankia is a root-associate
with many boreal shrubs, N2-fixing;
Bacterial Groups III
3. Purple and Green Bacteria
Photosynthesis without evolution of O2! Strict
anaerobes. Some use sulfur (see formula for
photosynthesis reaction in PSB), others use organic
compounds as electron donors. Ancestor or relative of
PNSB thought to be origin of mitochondria; P&GBs
have photosystems that appear ancestral to exisiting
photosystems I and II in green plants.
Bacterial Groups IV
4. Proteobacteria – majority of well-known
G- rods (Pseudomonas, Escherichia)
5. And many others …
ARCHAEA
1. Extreme halophiles (heterotrophs and a few are
photoheterotrophs: Halabacterium, using
bacteriorhodopsin as light receptor)
2. Extreme thermophiles (mostly anaerobes,
many also chemoautotrophs)
3. Methanogens (moderate, but anaerobic
environments; generate CH4 fromH2 and CO2 chemoautotrophs)
VIRUSES
• Nucleic acid (ds or ss DNA or RNA – i.e., 4 main
types) surrounded by a protein capsid
• Those that attack bacteria are called bacteriophages or
just phages
• Submicroscopic – can’t usually be seen with light
microscope at 1000x
• Main shapes are rods, bullets, polyhedrons, filaments
• Replicate using the host machinery, either by
incorporation into genomic DNA or piracy of it from
outside
Viruses
• Viruses are non-living entities according to
most definitions of life (e.g., being
composed of cells; reproducing and
metabolizing by themselves) and since they
are (now) dependent on other organisms
must (?) logically have come after the first
true life, which appears to have been
prokaryotes.
Viroids & Prions
• VIROIDS are infectious ssRNA
• PRIONS are infectious proteins (Mad Cow,
etc.)