Microbiology, Lec. 5

Announcement:

Please note that the next two lectures will cover parts of chapters 19 and 20.

Let's now discuss the major groups of microbes in more detail. We will discuss the major groups of Bacteria and Archaea and spend one lecture on a major group of the Eucarya, the Fungi (Lec. 8). Our purpose now is to expose you to these groups so you have a context to refer back to throughout the semester.

Let's start with the Gram-Negative Bacteria (Ch. 19 & 21). Chapter 19 covers the Proteobacteria and other heterotrophic gram-negative bacteria. Chapter 21 covers the photosynthetic and chemoautotrophic Bacteria (gram + and gram -). Our Basic outline for the gram negative bacteria will follow the book as closely as possible.....

Proteobacteria (= Purple Bacteria)

Heterotrophic Proteobacteria

Fermentative (facultative anaerobes)

Strict Aerobes

Other Proteobacteria

Prosthecate bacteria

Bdellovibrio

Myxobacteria

Cytophaga and Bacteroides Groups

Cytophaga

Bacteroides

Planctomyces group and Chlamydia

Spirochetes

Before we get too deeply into the groups of microbes let's review some physiological groupings that we will use in addition to our 16S phylogenies.

Heterotrophs - use organic carbon compounds as their carbon and energy sources (we are heterotrophs as are the fungi and many bacteria).

Autotrophs can fix carbon dioxide (CO2) from the air and turn it into organic molecules.

Photoautotrophs use light energy to do this (plants, cyanobacteria and many other bacteria are photoautotrophs).

Chemoautotrophs use chemical energy to fix CO2 (e.g. sulfur oxidizing bacteria and nitrifiers are chemoautotrophs).

GRAM - BACTERIA:

Proteobacteria (= Purple Bacteria)

The Proteobacteria are a huge group of organisms with as much metabolic diversity as the Plants and Animals combined. Taxonomy of this huge group is still in a state of flux so we will present them as functional groups with reference to phylogenetic groupings whenever possible. Appendix B in the book gives a fairly complete listing of the genera of the Proteobacteria and where each genus fits into the Alpha, Beta, Gamma, or Delta Proteobacteria.

Bacteria in this group include some of the most common human pathogens and bacteria of economic importance.

Let's start with the Proteobacteria that are facultative anaerobes

Fermentative Proteobacteria (facultative anaerobes)

Enteric Bacteria (all in the Gamma Proteobacteria). (enter = Gr. for gut), Table 19.2 shows some common genera of Enteric Bacteria. Note that the habitat for most of them is indeed in the intestines of some sort of animal.

Some Famous genera:

Salmonella (S. typhi causes typhoid fever)

Escherichia (E. coli)

Shigella (S. dysenteriae is closely related to E. coli)

Yersinia (Y. pestis causes plague)

Klebsiella (fixes N2 and can cause pneumonia)

Serratia

pErwinia

Table 19.5 shows some of the common tests for distinguishing between these and other enteric genera (you will do some of these tests in lab).

Other fermentative Gram negative bacteria include the genera Vibrio (vib = L. for whip mark), Photobacterium (bioluminescent) and Aeromonas (includes fish pathogens),.

One commonalty of most of the facultative anaerobes is that they are capable of living dual lives. For example, many bioluminescent bacteria can use their anaerobic capabilities to live in the guts of fish and their aerobic abilities to live in the light organs of fish or to survive in the aerobic waters of the open oceans.

Proteobacteria (cont.)

Strict Aerobes or oxidative Proteobacteria (can't ferment organic compounds)

We will discuss many bacteria in this group over the course of the semester. Important genera include:

Pseudomonas - polar flagella (Figure 19.6) and oxidase positive. A very large genus that is now being broken up into many different genera.

Alpha Proteobacteria:

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

Agrobacterium - tumor-like growths in plants

Acetic Acid Bacteria (vinegar bacteria) - covert ethanol to acetic acid. Some Acetobacter spp. can produce cellulose fibers (See Figure 17.21 in Stanier).

Prosthecate Bacteria (prosth = Gr. for appendage, addition) mostly members of the Alpha group of the Proteobacteria.

These are bacteria with weird shapes (that increase their surface area) and unusual life cycles (see Figures 19.18, 19.19, 19.20).

Finally, sequencing data also show that mitochondria from eucaryotic cells are most closely related to the alpha Proteobacteria. Two bacterial genera, Rickettsia and Ehrlichia, are especially closely related to mitochondria (see Figure 2 in Molecular Microbiology vol. 15(1), pg. 5). Both of these genera are obligate intra-cellular parasites of eukaryotes. Several members of the genus Rickettsia cause human diseases (e.g. Typhus and Rocky Mountain Spotted Fever) and the one described species of Ehrlichia, E. Chaffeensis, causes a tick-borne disease similar to Rocky Mountain Spotted Fever.

Sheathed Bacteria (Fig. 4.39) (Mostly Beta Proteobacteria)

e.g.

Sphaerotilus (Figs. 19.14, 19.15)

Leptothrix (Fig. 19.16)

Delta Proteobacteria:

Parasitic and predatory bacteria of the Delta Proteobacteria:

Bdellovibrio (bdell = Gr. for leech) were once thought to be viruses but they are just small bacteria that parasitize other gram negative bacteria (See Figure 19.28)

Myxobacteria are gliding bacteria some of which feed on other microorganisms. They also can have complex life cycles that include macroscopic fruiting bodies (see Figure 19.32).

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