Bacteria Helpful and harmful

Beneficial and Harmful
Bacteria break down large biological
molecules into more simple ones that can
be used by plants.
This is decay and can be harmful if what
is being broken down is food or
something that we do not want to see
Some bacteria can
change substances into
more useful forms.
Example: Nitrogen fixing
bacteria that live in the
roots of certain plants
called legumes (beans
and peas).
Bacteria can be used to
make vinegar (acetic acid
This is important is producing
sauerkraut, yogurt and
sourdough bread.
Some types of cloth need
bacteria to help in their
processing like linen and
Buttermilk and most
cheeses are made with
bacteria (some cheeses
are made with molds)
Bacteria are used to
make chemicals that
fight other bacteria
Some bacteria are used to kill insects
(bacillus thurigensis) BT
This cases a disease in caterpillars that
harm many important food plants.
Scientists have isolated the gene that
the bacteria use to produce a poison
that kills the insect larvae and inserted
it into the plant itself. Now the plant is
poisonous to the insects. BT corn and
Bt soybeans are banned in Europe.
They reduce butterfly populations.
Harmful effects and
how we fight them.
Food Spoilage - the bad side of decay bacteria
• Heating - kills bacteria
• Drying - no extra water to support bacteria. This is why
dried fruit and meat lasts so long.
• Salting - Kills many bacteria. They have trouble with
osmosis (remember that?)
• Smoking - keeps bacteria from growing. Many chemicals
that are in wood smoke kill bacteria. This is why ham was
• Cooling - this greatly slows down bacteria reproduction
rates. Why we have refrigerators.
•Pasteurization - controlled heating to destroy bacteria. usually
used in milk products
Bacteria cause direct harm to animals and plants by actively
living in them and casing disease or by producing chemicals
that are harmful.
Humans - many diseases. Strep throat, skin infections are
examples are examples of bacteria living on or in us. Some
bacteria produce toxins that are very dangerous. Clostridium
botulinum and Clostridium tetani are examples.
Animal diseases - Anthrax and cholera are examples.
Plant diseases - Blights and rots.

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