Microbiology, Lec 6.

sub-theme for the day: growth at environmental interfaces...

Gamma Proteobacteria (cont.)


Sulfur Oxidizers


Beggiatoa (gliding motility)

Thioploca large (15 - 40 Ám wide) relative of Beggiatoa that form huge mats off the coast of Chile (see Fossing et al. 1995. Nature vol. 374: 713 - 715)

Thiomicrospira - discuss transfer of H2S, O2 and CO2 to intracellular symbionts of tube worms.

Thiothrix (sheathed sulfur oxidizer)

discuss gradient cultures for Beggiatoa (see Hagen, K.D. and D.C. Nelson. 1996. Appl. Environ. Microbiol. 62: 947-953.)


Gamma Proteobacteria (cont.)

The Purple Sulfur Bacteria

Chromatium (See Figs. 22.18 and 41.14)

use H2, H2S or S as electron donor for photosynthesis (not H2O)

CO2 + 2 H2A ------> CH2O (cell material) + H2O + 2 A


Alpha Proteobacteria:

Rhizobium and Bradyrhizobium - Symbiotic N2 fixing partners of legumes (beans, peas, clovers etc.). (Figs. 22.8)

Chemical communication between plant and microbe (see Fig. 42.9)


Agrobacterium - tumor-like growths in plants (Fig. 22.9)

e.g. Crown Gall
transfer of bacterial DNA to the plant genome.....

Mitochondria - show tree.

rRNA of mitochondria from various Eucarya have been sequenced and the latest evidence I have seen indicates that they are alpha Proteobacteria most closely related to intra-cellular symbionts like Rhizobium and parasites like Agrobacterium and Rickettsia.
Acetic Acid Bacteria

(vinegar bacteria) - covert ethanol to acetic acid in the presence of O2.

ethanol ----> acetaldehyde -----> acetate
NADH re-generated by both steps.

Some Acetobacter spp. can produce cellulose fibers (See Figure 17.21 in Stanier).....why?

The vinegar from Chateau Schmidt is produced by an unknown strain of Acetic Acid Bacterium that forms a white crust on top of the old wine - (pass around a sample in class). A good lab project would be to identify this organism and see what makes it float...

Alpha Proteobacteria (cont.)

Prosthecate Bacteria (prosth = Gr. for appendage, addition)

These are gram - bacteria with weird shapes (that increase their surface area) that also have unusual life cycles (see Figures 22.4 - 22.7).

Caulobacter, Hyphomicrobium, Stella!


Delta Proteobacteria.

All are heterotrophs and many are predatory bacteria....

Bdellovibrio (bdell = Gr. for leech) were once thought to be viruses but they are just small bacteria that parasitize other gram negative bacteria (See Fig. 22.32)

Myxobacteria are gliding bacteria some of which feed on other microorganisms ("wolf packs"). They also can have complex life cycles that include macroscopic fruiting bodies (see Fig. 22.33 - 22.35).

Other Proteobacteria (from various proteo subgroups) that we don't have time to discuss or that we will discuss later: Legionnella, Neisseria, Rickettsia


Other Gram negative bacteria (Ch. 21)


discussed these guys in lec. 4

read pages 450 - 453.

many have never been cultured but they are found in many environments including our mouths


Spirochaeta(non-pathogens, anaerobic)
Borrelia (arthropod-borne diseases)
Cristispira (symbionts of molluscs, some very large)


Cyanobacteria (wait til lecture 13)


The Bacteroides and Cytophaga Group

contains all heterotrophs: many degrade complex organic substrates like cellulose, chitin, agar, keratin etc....

Cytophaga - Gliding motility, slime trails that stick them to the substrate. They release extracellular enzymes to release monomers from the polymers they are stuck to...

Bacteroides - One of the dominant genera in colons, rumens, cecums and other animal fermentation chambers. Approx 10 billion per g of human fecal material.


Planctomyces group and Chlamydia

Planctomyces are budding bacteria - many with unusual morphologies....

Chlamydia are intracellular, obligate parasites that cannot produce their own ATP. They are small (200 x 400 nm) and have a very reduced genome. They have a complex life cycle (Fig. 21.13). All known species are pathogens of humans or other animals...
C. Trachomatis causes trachoma and chlamydial venereal disease of humans.