LECTURE 14

GRAM POSITIVE

BACTERIA (cont.)

Bacillus thuringiensis - “Bt”

B. sphaericus

Both species form a parasporal body - a solid

protein crystal next to their spores.

These species of bacteria kill insects:

• B. thuringiensis - moth larvae

(caterpillars)

- beetle larvae

• B. sphaericus -

mosquito larvae

“Bt” is a popular organic insecticide

Genes from Bt have been integrated into several

plant genomes to give plants permanent

resistance to pests:

The Giant Bacterium - Epulopiscium

First isolated from a

surgeonfish

See Perspective 1.1, pg. 14

Assumed to be protozoa because of their size - up

to 600 uM

DNA sequencing showed however that Epulopisciumis a bacteria, not a protozoan.

These bacteria are closely related to Clostridia

and Bacillus.

In 1997, off the coast of Namibia, an even largerbacterium was discovered (See Perspective 1.1, pg. 14).

It’s as big as the head ofa fruit fly!

These bacteria, Thiomargarita namibiensis,

are not Gram + bacteria. Also giant

Beggiatoa-like Thioploca off the coast of Chile

These bacteria use H2S as an energy source and

nitrate as an electron acceptor.

Part of the reason that they’re so huge is that

as much as 98% of their cell is filled up with a

vacuole filled with nitrate.

Low GC Gm- cont.

Staphylococcaceae - Staphylococcus

• facultatively anaerobic, nonmotile, cocci

that form irregular clusters

Table 22.1. Note that the dominant organisms are adapted to

dry conditions.

Fig. 22.1. The skin as a complex landscape for

microbes. Note that High GC, Gm+ bacteria

dominate the deeper zones of the hair follicle.

These organisms produce fatty acids (e.g.

propionic acid) by fermenting oils from the

sebaceous gland.

Table 23.1

The Nose and upper respiratory tract

Staphylococcus aureus and S. epidermidisare the predominant bacteria in the nose.

See Table 23.1

20% (much higher % among hospital workers) ofhumans carry S. aureus, an opportunisticpathogen

Fig. 22.3. Boil or pimple formation caused by

coagulase-positive Staphylococcus aureus.

Low GC Gm- cont.

Lactic Acid Bacteria Fig. 6.23. Fermentations

• produce lactic acid as fermentationproduct

!Homolactic fermentation -only lactic acid (2 per sugar

fermented)

!Heterolactic fermentation -other things, too (usually 1 lactic

acid and 1 acetaldehyde or alcohol)

Table 32.1

Lactic acid bacteria are fermentativebacteria that can tolerate O2 but can't useO2 in their metabolism (aerotolerant).

Live in rich environments (like your throat or

milk) and have lost the ability (through

evolutionary time) to synthesize many aminoacids and vitamins.Such organisms are referred to asfastidious.

• Common genera are:

Streptococcus, Enterococcus, Lactococcus,

and Lactobacillus.

• Don’t produce spores

Streptococci (strept = Gr. for twisted)

• some are important pathogens (e.g. S.pneumoniae and S. mutans).

• very common inhabitants of the human body

and foods (will come back to in a few minutes…).

Homolactic fermentation (produce 2 lactic acid

for every glucose used in fermentation)

Fig. 11.3. Streptococcus spp.

Streptococcal Diseases

• various Streptococcus species

We will concentrate on tooth decay (dental cariestoday (read pgs. 602-604)

Later in semester…

Strep Throat (Steptococcal Pharyngitis, pgs. 565-569) and

A little bit about pneumonia (pgs. 576-579)

S. mutans is the primary cause of dental caries via an

plasmid-encoded enzyme dextransucrase which

catalyzes the following:

n sucrose ----> dextran + n fructose

Dextran is a sticky polymer (alpha-1,6 linkages) of

glucose molecules (we don’t have the enzyme to cleave that bond).

Remember S. mutans is also homofermntative so it also

converts every fructose from above to 2 lactic acids

n sucrose ----> dextran + 2n lactic acid

Caries are caused by this acid eating away at the

enamel….

Sucrose and S. mutans are needed

because S. mutans can’t cause caries without

sucrose…..

and S. mutans-free animals don’t get cavities even

in the presence of sucrose

Fig. 24.3. Dental Plaque. Many types

of Bacteria in a polysaccharide matrix.

Fig. 24.4 Increase in acidity after

sugar addition to dental plaque.

• Lactobacillus used to make many foods -yogurt, sauerkraut, beer, wine, cheese,sour dough bread…

Usually rods (see Fig. 11.4)can live at lower pHs than Streptococcus spp.thus is important in later stages offood fermentations (e.g. in yogurt, sauerkraut).

Homo- or heterolactic fermentors.

Fig. 11.4. Lactobacillus sp. in yogurt. Note denatured proteins

(= curdled milk)

Table 32.1

Succession in microbial communities - applications to

food spoilage and enhancement…..

Succession in foods is often related to pH changes due

to lactic acid bacteria……

Start with food spoilage see figure 30.4

Fig. 30.4

Natural successional processes can be

manipulated to enhance flavor and preserve

food….

Example of yogurt and cheeses…….

And then a bit on wine and vinegar….

making yogurtStreptococcus thermophilus,Lactobacillus bulgaricus (Lactobacillus delbruekii subsp. bulgaricus)

1. Pasteurize milk - kills most of the organisms in the milk (but not S.thermophilus).

2. Inoculate with yogurt

3. Incubate at 45°C (optimum for S. thermophilus). S. thermophilus growsand produces lactic acid.

4. Cool when chunky - encourages L. delbrueckii (opt. = 37°C); grow producinglactic acid and aromatic compounds (acetaldehyde) that contribute to theyogurt flavor.

Lactobacilli are more acid tolerant than Streptococci. Therefore theabove steps enhance a natural successional process.

Other organisms are added to yogurt:

Lactobacillus acidophilus (acidophilus)Bifidobacterium bifidum (see next lecture)Both can colonize the human colon;have therapeutic value for recovery from diarrhea etc.

Cheese….

Curd = coagulated (denatured) milk proteins surrounding fat

etc… caused by lactic acid bacteria and

rennin = an acid protease from calf stomachs (or

fungal acid proteases)

Curds are then ripened - 3 main ways to ripen cheese:

1) Original bacteria in the cheese (e.g. Parmesan, cheddar, Gouda, Swiss)

2) Microbes injected inside the cheese (e.g. blue cheese injected with the

fungus Penicillium roquefortii)

3) Microbes that grow on the cheese (e.g. brie and Camembert are covered with

Penicillium camembertii)

Fig. 32.3

Table 32.3

Let’s look at Soy Sauce (Shoyu) in a little more detail -

a succession of microbes based on release of different

organic constituents over time…..

Table 32.2

PYRUVATE

Alcoholic Fermentation - 2 step process

ACETALDEHYDE CO2

ETHANOL

+

NADH

NAD+

Used to make bread, wine, and beer.

The difference between white and red wines hasmostly to do with how long the must is exposed tothe skins (where most of the pigments are) and theoccurrence of the malo-lactic fermentation. In bothwhite and red wines yeast (Saccharomycescerevisiae) are usually added to the wine to performthe ethanol fermentation.But, many red wine grapes are picked before theyare completely ripe and as a result there is an excessof malic acid in the grapes (that would be convertedto sugar in ripe grapes). After the wine has set for awhile and most of the sugars are fermented, certainlactic acid bacteria (e.g. Lactobacillius spp.) carry outa fermentation that converts malic acid to lactic acidand CO2.

Fig. 32.04

The Malo-lactic fermentation (cont.)

Because malic is a dicarboxilic acid and lactic is amonocarboxilic acid, this reaction can cut the acidityof the wine by up to half - making for a more mellow wine.

COOH COOH HCOH ------> HCOH + CO2

CH2 CH3

COOHMalic acid Lactic acid

This step is absolutely essential for the production ofhigh quality red wines, especially in Burgundy andBordeaux, where the growing season is short.

Vinegar production from wine…….

by Acetobacter aceti (an aerobic alpha Proteobacterium) and

related bacteria that oxidize ethanol to acetic acid…..

Colonies of Acetobacter aceti (an alpha Proteobacterium) on

calcium carbonate agar. Zone of clearing indicates acetic acid

production……

One last microbial food…. Edible cyanobacteria

Spirulina platensis is used directly as food in parts of Africa

and now in Europe…

Spirulina platensis is harvested from seasonally dry ponds near

Lake Chad… The mats of bacteria are cut into cakes called

Dihe. Very high protein content (65%) and very high yield of

protein per acre in France (10 tons protein per acre as

compared to 0.02 for beef and 0.2 tons per acre for wheat).