BIOLOGY 304FEVOLUTION OF PLANTS

Fall 2008

Lecture 4Thursday September 25, 2008Chapter 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 90-100+ 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

AncestralCyanobacterium

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. ActinomycetesFilamentous Gram+; abundant in soil; odour of fresh soil = geosmin; some cause plant diseases, many very important in producing antibiotics, including ant-associates; Frankia is a root-associate with many boreal shrubs, N2-fixing;

Bacterial Groups III

3. Purple and Green BacteriaPhotosynthesis 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 …

ARCHAEA1. 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.)