Download LECTURE 14 GRAM POSITIVE BACTERIA (cont.)

Bacillus thuringiensis - “Bt”
B. sphaericus
LECTURE 14
GRAM POSITIVE
BACTERIA (cont.)
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
Genes from Bt have been integrated into several
plant genomes to give plants permanent
resistance to pests:
“Bt” is a popular organic insecticide
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 Epulopiscium
is a bacteria, not a protozoan.
These bacteria are closely related to Clostridia
and Bacillus.
In 1997, off the coast of Namibia, an even larger
bacterium was discovered (See Perspective 1.1, pg. 14).
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.
It’s as big as the head of
a fruit fly!
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
Table 22.1. Note that the dominant organisms are adapted to
dry conditions.
• facultatively anaerobic, nonmotile, cocci
that form irregular clusters
Table 23.1
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.
Low GC Gm- cont.
The Nose and upper respiratory tract
Staphylococcus aureus and S. epidermidis
are the predominant bacteria in the nose.
See Table 23.1
20% (much higher % among hospital workers) of
humans carry S. aureus, an opportunistic
pathogen
Fig. 22.3. Boil or pimple formation caused by
coagulase-positive Staphylococcus aureus.
Lactic Acid Bacteria
Fig. 6.23. Fermentations
• produce lactic acid as fermentation
product
!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 fermentative
bacteria that can tolerate O2 but can't use
O2 in their metabolism (aerotolerant).
Live in rich environments (like your throat or
milk) and have lost the ability (through
evolutionary time) to synthesize many amino
acids and vitamins.
Such organisms are referred to as
fastidious.
• Common genera are:
Streptococcus, Enterococcus, Lactococcus,
and Lactobacillus.
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…).
• Don’t produce spores
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 caries
today (read pgs. 602-604)
Later in semester…
Strep Throat (Steptococcal Pharyngitis, pgs. 565-569) and
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).
A little bit about pneumonia (pgs. 576-579)
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 of
food 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
Fig. 30.4
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
making yogurt
Streptococcus thermophilus,
Lactobacillus bulgaricus (Lactobacillus delbruekii subsp. bulgaricus)
Natural successional processes can be
manipulated to enhance flavor and preserve
food….
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 grows
Example of yogurt and cheeses…….
And then a bit on wine and vinegar….
and produces lactic acid.
4. Cool when chunky - encourages L. delbrueckii (opt. = 37°C); grow producing
lactic acid and aromatic compounds (acetaldehyde) that contribute to the
yogurt flavor.
Lactobacilli are more acid tolerant than Streptococci. Therefore the
above 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
Table 32.2
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…..
Alcoholic Fermentation - 2 step process
PYRUVATE
ACETALDEHYDE
+
CO2
NADH
ETHANOL
NAD+
Used to make bread, wine, and beer.
Fig. 32.04
The difference between white and red wines has
mostly to do with how long the must is exposed to
the skins (where most of the pigments are) and the
occurrence of the malo-lactic fermentation. In both
white and red wines yeast (Saccharomyces
cerevisiae) are usually added to the wine to perform
the ethanol fermentation.
But, many red wine grapes are picked before they
are completely ripe and as a result there is an excess
of malic acid in the grapes (that would be converted
to sugar in ripe grapes). After the wine has set for a
while and most of the sugars are fermented, certain
lactic acid bacteria (e.g. Lactobacillius spp.) carry out
a fermentation that converts malic acid to lactic acid
and CO2.
The Malo-lactic fermentation (cont.)
Because malic is a dicarboxilic acid and lactic is a
monocarboxilic acid, this reaction can cut the acidity
of the wine by up to half - making for a more mellow wine.
COOH
COOH
HCOH
------> HCOH
+
CH2
CH3
COOH
Malic acid
Lactic acid
CO2
This step is absolutely essential for the production of
high quality red wines, especially in Burgundy and
Bordeaux, 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).