Bacterial Growth and Reproduction

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?


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!


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.

Methods of 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.


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.


(Pinching)


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-)


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.


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.

Importance of Bacteria

Foods:◦Beverages, cheese, yogurt, buttermilk, sour

cream, pickles, vinegar, sauerkraut…


Industrial Uses:◦Clean up oil spills, mining of minerals from the

ground, remove wastes and poisons from water…


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?


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.


Cattle also have a symbiotic relationship with bacteria.

◦They do no 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!

Bacteria in the Environment

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).

Energy in Bacteria

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.

Food for Bacteria: Autotrophs

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: Heterotrophs

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.

Energy from Food

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

Bacterial Growth and Reproduction

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