Bacterial Growth and
Reproduction

If bacteria are capable of dividing every
20 minutes, and if environmental
conditions are favorable, how many would
we have after just 48 hours?
Rate of Bacterial Growth and
Reproduction

If bacteria are capable of dividing every
20 minutes, and if environmental
conditions are favorable, how many would
we have after just 48 hours?
◦ 4000 times the mass of the Earth!
Rate of Bacterial Growth and
Reproduction
Thankfully this situation does not happen
in real life.
 What are two main factors that serve to
keep the reproduction of bacteria in
check?

◦ 1. The availability of food.
◦ 2. The production of waste products.
Rate of Bacterial Growth and
Reproduction

Binary Fission:
◦ Bacteria divide by binary fission when they
(approximately) double in size.
◦ Their surface area to volume ratio gets to be
too low.
Methods of Reproduction

Binary fission is a form of asexual
reproduction because:
◦ It involves no recombination of genetic
material, so daughter cells are clones of parent
cells.
◦ There is one parent only, no fusion of gametes
to produce a daughter cell.
Methods of Reproduction
(Pinching)
Methods of Reproduction

Conjugation:
◦ Some bacteria reproduce by a form of sexual
reproduction called conjugation.
◦ After conjugation is complete the bacteria will
divide by binary fission as usual.
◦ During conjugation:
 Bacteria transfer genetic material from one
cell to another along a protein bridge.
 Donor  Recipient (F+  F-)
Methods of Reproduction
Methods of Reproduction

Spore Formation:
◦ This involves the formation of endospores.
◦ This can happen when growth or environmental
conditions become unfavorable.
◦ An endospore has a thick internal wall that
encloses the DNA and part of the cytoplasm.
Methods of Reproduction

Spore formation helps the species survive,
but it is not actually a form of
reproduction because the endospore does
not reproduce, it just remains dormant for
a certain period then opens up and the
bacteria begin to grow again.


No reproduction takes place.
Methods of Reproduction

Foods:
◦ Beverages, cheese, yogurt, buttermilk, sour
cream, pickles, vinegar, sauerkraut…
Importance of Bacteria

Industrial Uses:
◦ Clean up oil spills, mining of minerals from the
ground, remove wastes and poisons from
water…
Importance of Bacteria

A symbiotic relationship is one in which
two organisms live together and one or
both benefit from the partnership.

Bacteria and humans have a “win-win”
symbiotic relationship:
◦ With E. coli?
Importance of Bacteria
The E. coli bacteria live in the colon.
 They are provided with warmth, shelter
and food from the large intestine of
humans.
 Humans get the production of vitamins
and the breakdown of waste material
from the bacteria.

Importance of Bacteria

Cattle also have a symbiotic relationship
with bacteria.
◦ They do not produce the enzymes (neither do
we) necessary to break down cellulose (the
main carbohydrate) in grass and hay.
◦ Bacteria in their intestines can make these
enzymes allowing that digestion of the food!
Importance of Bacteria
Bacteria are essential to life on Earth.
 Without them, plants and animals would
use up all of the essential minerals
needed for life.


Bacteria break down, decompose and
recycle dead material and return
usable minerals back into the ground
and enrich the soil.
Bacteria in the Environment

Many bacteria are heterotrophic
saprophytes:
◦ These are bacteria that do not make their own
food.
◦ They get their nutrition from the
molecules of once living things (a.k.a. dead
organisms).
Bacteria in the Environment

So far we have seen a few different ways
to identify different bacteria:
◦ 1. Carbohydrates in cell walls: Gram+ = 1
layer, Gram- = 2 layers
◦ 2. Shape: round, rod, spiral
◦ 3. Grouping: chains (strepto), clusters
(staphylo)
◦ 4. Flagella: none, 1, 2, etc.
◦ 5. Colony or colour on a streak plate
Energy in Bacteria

We can also identify bacteria by the
lifestyle they lead:
◦ Today we will look at how they obtain food.
Energy in Bacteria

Phototrophic Autotrophs:
◦ They use photosynthesis to make food from
sunlight.
◦ i.e. blue/green algae or cyanobacteria
Food for Bacteria: Autotrophs

Chemotrophic Autotrophs:
◦ They make food from inorganic molecules like
sulfur, iron, oxygen and ammonia.
◦ They live in harsh environments.
◦ i.e. archaebacteria
Food for Bacteria: Autotrophs

Phototrophic Heterotrophs:
◦ They use sunlight for energy, but they also
need organic molecules for nutrition.
Food for Bacteria: Heterotrophs

Chemotrophic Heterotrophs:
◦ They get their food from obtaining organic
molecules then breaking them down and
absorbing them.
◦ Things that do this:
 Salmonella, humans, animals…
◦ They compete with us for food, but produce
toxins that give us food poisoning.
Food for Bacteria: Heterotrophs

There are two ways that bacteria can get
the energy out of the food:
◦ Respiration
◦ Fermentation
Energy from Food

Respiration
◦ Uses oxygen to get energy from food.
◦ This is the more efficient way compared to
anaerobic.

Obligate Aerobes
◦ These are strictly aerobes
◦ They need to live in O2
◦ Most eubacteria fit here
Energy from Food

Fermentation
◦ They get energy from food without using
oxygen.

Obligate Anaerobes
◦
◦
◦
◦
◦
They are strictly anaerobes
They must live in the absence of oxygen
They are poisoned by oxygen
They live in the soil or deep in the Earth
Ex. Botulism, tetanus and most
arachaebacteria
Energy from Food

There are also Facultative Anaerobes:
◦ They do not need air, but they can use it, and
most actually prefer it.
◦ They are not poisoned by oxygen
◦ Ex. E. coli, Listeria
Energy from Food
Energy from Food