Microbiology,

Lec. 11, Energy-Yielding (Catabolic) Pathways (cont.)

Fermentations.

Fermentation =

Organic compounds are e- donors and organic intermediates (= breakdown products) are e- acceptors. Because part of the original substrate acts as the e- dump, fermentations yield many fewer ATPs than respiration. see Fig. 9.13. All ATP production is via substrate-level phosphorylation

In nature one can find fermentative microbes wherever there is a paucity of terminal e- acceptors. Many microbes can also switch from respiration to fermentation in their own metabolisms; remember Enteric and other fermentative Gamma Proteobacteria, Lecture 5. As another example, when yeast cells are added to fruit juice they initially carry out aerobic respiration (sugars are e- donor, O2 is e- acceptor) and then switch to fermentation as the O2 runs out.

The diversity of fermentations

Fermentation of sugar to ethanol: Draw on Board (or fill in blanks in Fig. 9.13)

Other Fermentations

Show figure "fate of pyruvate" (Fig. 9.14)

point out industrial products (read box 9.1, pg. 177) and some of the fermentations that we already talked about when we discussed Propionibacterium, Bifidobacterium, and the lactic acid bacteria etc. See lecture Lecture 7.....

Many fermentations don't involve sugars.... show Table.....

Examine a few fermentations in a little more detail...
some are quite complex:

Figure 9.14

Show Figure for conversion of lactic acid to propionic acid by some Propionibacterium spp. and other pathways for propionate production in other Propionibacterium spp. (e.g. Fig. 9.14 #3). Note CO2 production.

A neat variation on the theme of e- flow in fermentations is the "Stickland Reaction" as carried out by members of the genus Clostridium...(pg. 493)
overall rxn.:
2 glycine + alanine + ADP + Pi ----> 3 acetate + 3 NH4+ +ATP
show Figure

Anabolic processes (Chapter 11)

Anabolic reactions in cells are almost always linked to catabolic reactions (via ATP, reducing power and common pathways). We will not spend a lot of time memorizing individual pathways, but I'd like you to understand the overview of how anabolic and catabolic pathways are linked.

Figure in the book gives an overview of this linkage in autotrophs and heterotrophs. Remember that ATP and NADH are also needed to build macromolecules.

Figure ?? gives a global overview of anabolic reactions in a typical bacterium (E. coli).