Lecture 5: Growth of Microorganisms

Microbial growth is defined in terms of

Increase number of cells

True or false: Microbial growth is defined in terms of size.

False

List two ways bacteria divide.

1) binary fission

2) budding

binary fission

type of asexual reproduction in which an organism replicates its components and divides in half, producing two identical daughter cells

Binary fission steps

1. Cell elongates and DNA is replicated

2. DNA moves to oposite sides of the cell

3. Septum (partition) forms, completely separating the two DNA copies

4. Cells separate

Budding

List the phases of bacterial growth

four major phases:

1. lag phase

2. log (logarithmic) phase

3. stationary phase

4. decline phase or death phase

Define media.

a mixture of substances on or in which microorganisms grow

standard growth curve

A curve with four phases that represents the growth of a population of microorganisms grown in a closed culture

What occurs in the lag phase?

bacteria...

1) grow in size

2) synthesize enzymes

3) incorporate various molecules

from the medium

4) produce large quantities of energy in the form of ATP

True/false: Bacteria are metabolically active in the log phase.

True

Why do bacteria not significantly grow in size in the lag phase?

bacteria are adjusting to the new medium

What determines the length of the lag phase? (2)

1. type of bacterial species

2. conditions in the media

log phase

after bacteria adapt to media they experience logarithmic, or exponential, increase in population

generation time

the time it takes for a population to double

synchronous growth

Hypothetical pattern of growth during the log phase in which all the cells in a culture divide at the same time

appears as a stair-step line

asynchronous growth

all the cells in a culture divide at different times

appears as a smooth line

stationary phase

number of cells stays constant

cell division decreases to the point that new cells are produced at the same rate as old cells die

This phase of the standard bacterial growth curve is represented by a horizontal line.

stationary phase

Why is there not a significant amount of growth in the stationary phase?

1) medium contains low amount of nutrients

2) medium may contain toxic quantities

3) oxygen supply may become inadequate for aerobic bacteria and damaging pH changing may occur

Decline (death) phase

the number of live cells decreases at a logarithmic rate

This phase of the standard bacterial growth curve is represented by a straight downward-sloping diagonal line.

the decline (death) phase

involution

bacteria assume a variety of shapes under unfavorable conditions

Why do cells die in the decline phase?

conditions in the medium become less and less supportive of celldivision, many cells lose their ability to divide, and thus the cells die

True/False: In spore-forming organisms, more spores than vegetative cells survive during the decline phase.

True

Define colony

all the descendants of the original cell

Where on the solid media does the cells grow rapidly?

At the edges

Where on the solid media do the cells grow slowly?

Near the center of the media

Why do cells in the center of the media grow slowly?

they have smaller quantities of available nutrients and are exposed to more toxic waste products

Physical factors that affect bacterial growth (6)

•pH

•temperature

•oxygen concentration

•moisture

•hydrostatic pressure

•osmotic pressure

Nutritional (biochemical) factors that affect bacterial growth

•carbon

•nitrogen

•minerals (sulfur, phosphorus and other trace elements)

•vitamins

Define optimum pH.

the pH at which they grow best

List the classifications for pH.

-acidophiles

-neutrophiles

-alkaliphiles

True/False. Some bacteria can tolerate the full pH range.

False.

True/False. Many bacteria tolerate a pH that overlaps two categories.

True

Define acidophiles

acid-loving

grow best at a pH of 0.1 to 5.4

Give an example of an acidophile.

Lactobacillus, which produces lactic acid

Some bacteria that oxidize sulfur to sulfuric acid

Define Neutrophiles

exist from pH 5.4 to 8.0

Most of the bacteria that cause disease in humans are ___________ (pH classification )

Neutrophiles

Define Alkaliphiles

alkali-loving (base-loving) organisms, exist from pH 7.0 to 11.5

Give an example of an acidophile

Vibrio cholerae, the causative agent of the disease cholera, grows best at a pH of about 9.0.

Agrobacterium (soil bacterium) grows in alkaline soil of pH 12.0.

What component is incorporated into growth media to maintain proper pH levels?

Phosphate salts (buffer)

Buffer

A solution that minimizes changes in pH when extraneous acids or bases are added to the solution.

Why is a buffer (phosphate salts) required for growth media?

Bacteria produce large amounts of acid during metabolism causing changes in the pH of the medium

Changes in pH impact the growth of the bacteria

How are bacteria classified based on their temperature requirements?

-psychrophiles

-mesophiles

-thermophiles.

Obligate

the organism must have the specified environmental condition.

Facultative

the organism is able to adjust to and tolerate the environmental condition, but it can also live in other conditions.

Psychrophiles

cold loving, grow best at 15° to 20°C

mostly live in cold water and soil

Mesophiles

which include most bacteria, grow best at temperatures between 25° and 40°C

What temperature do most human pathogens grow at?

37C

Define obligate psychrophiles

Cannot grow above 20°C

Define falcultative psychrophiles

which grows best below 20°C but also can grow above that temperature

Define thermoduric organisms

mesophiles that can withstand short periods of exposure to high temperatures

Example of thermoduric organisms

Inadequate heating during canning or in pasteurization may leave thermoduric organisms alive and therefore able to spoil food

Define thermophiles.

or heat-loving organisms, grow best at temperatures from 50° to 60°C

Found in compost heaps and tolerate up to 110°C in boiling hot springs.

obligate thermophiles

grow only at temperatures above 37°C

facultative thermophiles

which can grow both above and below 37°C

What determines the optimum temperature in which an organism grows?

Enzymes within the organism

List the 3 critical temperature ranges of an organism.

1. Minimum growth temperature

2. Maximum growth temperature

3. Optimum growth temperature

Define minimum growth temperature.

the lowest temperature at which cells divide

Define maximum growth temperature.

the highest temperature at which growth is possible

Define maximum growth temperature.

the temperature at which cells divide most rapidly (shortest generation time)

Enzyme activity doubles for every _____ C rise in temperature until the high temperature begins to denature the enzymes.

10C

Give an example on how temperature can prevent bacterial growth.

Refrigeration of found at 4C to reduce growth of psychrophiles

True/False: Enzymes only denature by heat never extreme cold conditions.

True

What categories can further divide heterophiles?

Aerobes and anaerobes

Define obligate anaerobe

Organisms that can't live in the presence of oxygen.

Ex: Pseudomonas

Define obligate aerobe

Killed by free oxygen

Ex. Clostridium botulinum

C.tetani and bactericides

Which bacteria type grows near the surface of the nutrient broth?

Obligate aerobe

Which bacteria type grows near the bottom of the tube

Obligate anaerobe

Define microaerophiles

grow best in the presence of a small amount of free oxygen

Define facultative anaerobe

can survive with or without oxygen

True or false: All actively metabolizing cells generally require a water environment

True

dormant state

waiting for proper conditions to begin growth

Define hydrostatic pressure

pressure exerted by standing water,

define barophiles

pressure-loving" bacteria that live at high pressures, but die if left at standard atmospheric pressure for only a few hours

What happens to cells in hyper osmotic environments?

Cells lose water and undergo plasmolysis or shrinking of the cell

Define plasmolysis

the process in which cells lose water and shrinks in a hypertonic environment

Define halophiles

salt loving require moderate to large quantities of salt (sodium chloride

Where are halophiles found?

In the ocean where the salt concentration is around 3.5%

Extreme halophiles require salt concentrations between ____% and ___%

20%-30%

Define Fastidious

have complex nutritional requirement that is difficult to meet in the laboratory

Give an example of a fastidious bacteria.

microorganisms that cause Gonorrhea

List the two categories for bacteria based on carbon and nitrogen requirement.

1. Autotrophs

2. Heterotrophs

True/False. Fastidous organisms have all 20 acidic acids they require to grow.

False. Certain fastidious organisms require all

List the nutritional requirements of bacteria. (6)

1. Carbon

2. Nitrogen

3. Sulfur

4. Phosphorus

5. Trace elements

6. Vitamins

Define autotroph

Organism that has the ability to make its own food

Define heterotroph

Organisms that obtain food by consuming other living things

Why do bacteria require carbon?

Most bacteria use some carbon-containing compound as an energy source (vs.) many use carbon-containing compounds as building blocks to synthesize cell components.

Why do bacteria need nitrogen?

to synthesize enzymes, other proteins and nucleic acids

Why do bacteria require sulfur?

to make proteins, coenzymes, and other cell components

Why do bacteria require phosphorus?

use phosphorus (as phosphate) to synthesize ATP, phospholipids, and nucleic acids

Which trace elements do bacteria require?

Copper

Iron

Zinc

Cobalt

(In the form of ions)

Why do gram + bacteria require calcium?

Gram + require calcium for their cell wall

Why do spore-forming bacteria require calcium?

Synthesis of spores

Define vitamin

is an organic substance that an organism requires in small amounts and that is typically used as a coenzyme

Why do bacteria require trace elements?

Trace elements serve as cofactors in enzymatic reactions

Give examples of vitamins that bacteria require.

Folic acid

Vitamin B12

Vitamin k

How do bacteria obtain vitamins? (2)

1) some bacteria obtain vitamins from the host in order to grow

2) some gut flora (normal bacteria in the gut) synthesize vitamin k and other vitamins in their own benefiting the host

Define nutritional complexity.

the number of nutrients a microorganism must obtain in order to grow