Chapter 4:Dynamics ofProkaryotic

Growth

Important Point:

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Eac

h S

peci

es is

Uni

que Bacteria are incredibly diverse, but...

Each bacterial species can grow in only a limited set of environments.

Each bacterial species can grow only if presented with the right nutrients/conditions.

In addition, bacteria produce characteristic by-products (e.g., waste products).

We can take advantage of these growth characteristics to identify bacteria phenotypically.

To do these identifications we first have to get organisms in Pure Culture.

Unfortunately, only about 1% of microorganisms currently can be grown in pure culture.

Pur

e-C

ultu

re B

asic

s Sterile = completely free of microbes.

Aseptic Technique = procedures that minimize unintentional introduction of microorganisms to media (cultures) or from cultures to surrounding environment.

Solid media is usually employed to obtain pure cultures.

Agar is usually employed to make solid media.

Agar melts at 95°C and solidifies below 45°C.

Colony = pile of cells descended from single cell (or clump of cells).

Petri Dish = container to which agar is added to obtain pure culture.

Agar Plate (plate) = agar-containing petri dish.

(mostly) Isolated Colonies

Streak-Plate Method

Sto

ring

Pur

e C

ultu

res

Stored pure cultures are often called “Stock Cultures”

Stock cultures often are stored as/using: Frozen in glycerol solution Lyophilized = freeze drying On agar slants As stabs

Bin

ary

Fis

sion

This is how most bacteria undergo cell division (how they replicate).

The interval, division to division,

is called the Generation or

Doubling Time.

Note that not all daughter cells fully

separate after division, e.g.

streptococci, etc.

Env

ironm

enta

l Fac

tors

Opt

imum

Gro

wth

Tem

pera

ture

Growth temperature optimum.

Tem

pera

ture

Ran

ges

Max due to enzyme

denaturation.

Min due to enzyme & membrane

fluidity problems.

Psy

chot

roph

s

Important for food

spoilage.

Mes

ophi

les

Most human pathogens are mesophiles.

I.e., organisms adapted to growth at body

temperature.

The

rmop

hile

sImportant source of

heat-stable enzymes (e.g., Taq polymerase or

laundry detergent enzymes).

Oxygen Requirements: The Shake Tube

Oxygen Requirements: The Shake Tube

Note maximum growth nearer to surface (where oxygen is

plentiful; this is not shown well in image).

Don’t worry about enzyme names. Just recall “O2 (product)

detoxification”.

Aerotolerant Anaerobe!

Medically Important Examples

Pseudomonas spp. are obligate aerobes.

Enterics such as Escherichia coli are facultative anaerobes

E.g., Clostridium spp. such as C. botulinum.

Water AvailabilityPlasmolysis

Food preservation: jams, jellies, bacon, anchovies, etc.

Ter

ms

for

Nut

rient

Nee

ds Heterotrophs = require organic carbon (e.g.,

glucose).

Autotrophs convert CO2 to organic carbon.

Carbon fixation = conversion of CO2 to organic carbon.

Nitrogen fixation = conversion of N2 to non-gaseous form (i.e., ammonia).

Growth factors = small organic molecules (e.g., vitamins, amino acids) that must be provided for growth (some bacteria require no “exogenous” “growth factors”).

E.g., Neisseria spp. can require 40 growth factors to grow. We would describe such a bacterium as fastidious.

E. coli requires no growth factors. We would describe such a bacterium as non-fastidious.

Energy & Carbon Source Types

“Chemoautotroph” is good enough for

now.“Chemoheterotroph” is good enough for now.

Chemoheterotrophs differ in the number (and types) of organic compounds they can use. Some Pseudomonas species can utilize 80 different compounds. Other bacteria are limited to as little as only a single organic compound type.

Culture Media Types

Peptone = predigested protein

Culture Media Types

Note that, confusingly, many media are both selective and differential, e.g., MacConkey agar.

Enrichment Culture

Means of isolating rare organisms with specific

characteristics from heterogeneous

populations.

Direct Microscopic Count

Direct Microscopic Count

Requires relatively high bacterial densities.

Usually can’t distinguish living cells from dead cells.

Via

ble

Cou

nts:

Pla

te C

ount

s

Via

ble

Cou

nts:

Pla

te C

ount

sQuantifies number of

cells (CFUs) capable of replicating.

Note the enumeration

of colony-forming units

(CFUs).

Ser

ial D

ilutio

ns

Note Serial

Dilution.

Most Probable Number (MPN)

These are gas-filled tubes, an indication of bacterial growth

(fermentation).

Looking for sufficient dilution

that ~half of tubes show growth.

Reciprocal of that dilution

bacterial density.

Most Probable Number (MPN)

Useful particularly when enumerating

organisms that won’t grow on/in

agar media.

Durham tube.

Growth Curve

Growth Curve

Time of gearing up for division following change

in culture conditions.

Division at constant rate (exponential).

Death rate = Birth rate.

Constant per-capita death rate (exponential).

Phase of Prolonged Decline

Con

tinuo

us C

ultu

re, C

hem

osta

t

Chemostats are a means of keeping

a culture in log phase indefinitely.

Bio

film

s Biofilms are polysaccharide-encased bacterial

communities attached to environmental surfaces.

Biofilms include slippery rocks (in aquatic environments), slime coating sink drains, yuck yucking up what was once your clean toilet bowl, tarter on your teeth, etc.

“It is estimated that 65% of human bacterial infections involve biofilms.”

“Biofilms are particularly troublesome because they protect organisms against harmful chemicals such as disinfectants” and antibiotics.

They can accumulate on non-sterile medical devices kept in contact with patients over relatively long periods, e.g., on catheters.

Cha

pter

6 N

otes

Don’t worry too much about the details of Glycolysis, Cellular Respiration, or Photosynthesis onward.

These topics are covered on pp. 144-151 and pp. 156-163.

Note, however, that we will cover Glycolysis and Cellular Respiration in class at least from the perspectives of the importance of NAD+ regeneration.

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