Transcript Aspergillus flavus

• Some grains are susceptible to spoilage.
– Aspergillus flavus produces aflatoxins that
accumulate in grains, nuts, and corn.
• Aflatoxins are linked to liver and colon cancers.
– Ergotism occurs when Claviceps purpurea
deposit toxins in rye, wheat and barley.
• They may induce convulsions and hallucinations.
• Milk and dairy products sometimes sour.
– Milk is an excellent source of nutrition for humans and
microbes.
– Milk sours when bacterial enzymes digest fats into fatty
acids.
– Curdling occurs when bacteria ferment lactose into:
• lactic acid,
• acetic acid.
– Some bacterial species cause curdling by breaking down
casein proteins
• This is a critical step in cheese production.
• Drying and osmotic pressure help preserve
foods.
– Dry foods cannot support microbial
growth.
– Lyophilization (freeze-drying) involves
deep-freezing then vacuum pumping off
water.
– Osmotic pressure causes water to
diffuse out of cells, causing dehydration
and death in highly salted or sugared
foods.
• Many milk products are the result of fermentation.
– Fermentation of lactose by bacteria makes:
• buttermilk.
• acidophilus milk.
• sour cream.
– Dry milk solids containing
active bacterial cultures are
added to boiled milk to form yogurt.
– Cheese production begins when casein curdles out of milk.
• The curd (unripened cheese) is sold as
– cottage cheese.
– pot cheese.
– cream cheese.
26.1 Water Pollution
• Unpolluted and polluted water contain different microbial
populations.
– Unpolluted water contains low organic nutrients, thus low
numbers of microbes.
– Water can be polluted with
• sewage.
• agricultural runoff.
• industrial pollutants.
– Polluted water is high in
• organic matter.
• coliform and noncoliform bacteria.
• Biofilms are prevalent in the environment.
– A biofilm is an immobilized population of microbes tangled
together in fibers adhering to a surface.
– Microbes in a biofilm work together for
• nutrient storage production
• predator protection
• communicate with each other by quorum sensing
– Biofilms are used in
bioremediation to
degrade toxic wastes.
– Biofilms can form in the
human body and on
medical instruments.
FIGURE 08: Biofilm contamination
Courtesy of Dr. Rodney M. Donlan and Janice Carr/CDC
• The bacteriological analysis of water tests for indicator organisms.
– Presence of indicator organisms shows that water has been
contaminated by feces.
– Coliform bacteria live in mammalian intestines but can survive
in water.
– The membrane filter technique and standard plate count (SPC)
are used to determine numbers of bacteria in a water sample.
– The most probable number (MPN) test determines number of
bacteria by observing carbon dioxide gas production.
• Nitrogen-fixing microbes live symbiotically with
legume roots.
– They provide the plant and surrounding soil with usable
nitrogen.
– Streptokinase breaks
down blood clots formed
during a heart attack.
– Hyaluronidase facilitates
absorption of fluids
injected under the skin.
– Lactones produced by
species of fungi are used
for flavor and aroma
enhancement.
© Maximilian Stock LTD/Phototake/Alamy Images
Figure 01B: A pharmaceutical
technician monitors a series of
fermentors.
27.3 Other Microbial Products
• Many antibiotics are the result of industrial
production.
– Penicillin was the first antibiotic to be produced on an
industrial scale.
– Antibiotic production can involve fermentation,
producing natural antibiotics or semisynthetic drugs.
– Bacillus thuringiensis produce a toxin (Bt-toxin) during
sporulation that is deposited on leaves.
• If ingested by caterpillars, the toxin lyses the gut wall causing
paralysis and bacterial invasion.
• It seems to be harmless to plants and humans.
• Through biotechnology cotton and corn plants
carrying the Bt-toxin gene have been
developed that kill only insects that eat them.
• Fungal organisms are also being commercially
developed.
– Yeast cells are grown in fermentors.
• They are sold as dry yeast or compressed yeast cakes.
– Many species of mushrooms are grown on farms.
• High humidity and cool temperatures are required for
mushroom growth.
FIGURE 08b:
A mushroom farm
© Mashkov Yuri, Itar-Tass/Landov
• Bioremediation helps
clean up pollution
naturally.
– Naturally occurring
Pseudomonas species can
be stimulated to degrade
oil in spills.
– Species of Arthrobacter
degrade oil and allow
plant growth in spill
regions.
FIGURE 09: The Exxon Valdez oil spill
Courtesy of the Exxon Valdez Oil Spill Trust Council/NOAA