Microbio CH8-9A

Microbial Growth

An increase in the number of cells

How is microbial growth defined differently from growth in other organisms?

It is an increase in the number of cells, rather than in size

Requirements for microbial growth

Chemical and physical

Chemical requirements for growth

Carbon, nitrogen, and oxygen

In general, nutrients provide ______ and ______ for growth and survival

Energy; building blocks

What is the role of carbon?

Provides the backbone of all organic molecules

What is the role of oxygen?

Essential for obligate aerobes, deadly for obligate anaerobes

What is the role of nitrogen?

For protein and nucleic acid synthesis

Based on the energy source, organisms are either:

Phototrophs, whose energy source is light; Chemotrophs, whose energy source is chemical compounds

Based on the Carbon source, organisms are either:

Autotrophs, whose carbon source is CO2; Heterotrophs, whose Carbon source is organic compounds

In which group are medically important microbes? Why?

Chemoheterotrophs, because the human body has many organic molecules that provide an ideal environment to extract both the energy and carbon needed

Why is oxygen toxic for anaerobes?

Toxic forms of oxygen are highly reactive and excellent oxidizing agents, which resulting oxidation causes irreparable damage to cells

The Four Toxic Forms of Oxygen

Singlet oxygen, superoxide radicals, peroxide anion, and hydroxl radical OH

Hydroxyl radical OH

Most reactive, from ionizing radiation

Peroxide Anion

Formed during lipid breakdown and through reactions catalyzed by enzymes

What does Superoxide dismutase (SOD) do?

Protects, but absent in anaerobes

What does catalase do?

Converts hydrogen peroxide (2H2O2) into water (2H2O) and oxygen gas (O2)

What does peroxide do?

Converts hydrogen pyroxide (H2O2), without producing oxygen gas (O2)

Superoxide radicals

Byproduct of metabolism in the presence of O2

Singlet oxygen

High energy electrons from aerobic respiration

Effect of oxygen on growth in Obligate aerobes

Only aerobic growth; oxygen required

Effect of oxygen on growth in Facultative anaerobes

Both aerobic and anaerobic growth; greater in oxygen

Effect of oxygen on growth in Obligative anaerobes

Only anaerobic growth; ceases in oxygen

Effect of oxygen on growth in Aerotolerant anaerobes

Only anaerobic growth, but continues in presence of oxygen

Microaerophiles

Only aerobic growth; oxygen required in low concentrations

What does growth look like in obligate aerobes?

Growth occurs only where high concentration of oxygen have diffused

What does growth look like in facultative anaerobes?

Growth is best where most oxygen is present, but occurs throughout tube

What does growth look like in obligate anaerobes?

Growth occurs only where there is no oxygen

What does growth look like in aerotolerant anaerobes?

Growth occurs evenly; oxygen has no effect

What does growth look like in microaerophiles?

Growth occurs only where a low concentration of oxygen has diffused

Nitrogen fixation

Process that converts nitrogen gas (N2) into compounds like ammonia (NH3) or nitrates (NO3)

At the temperature extremes, how are membranes affected?

Too low temperature makes membranes rigid and fragile, while too high temperature makes membranes too fluid and leaky

Protein denaturation

Collapse of the cytoplasmic membrane; thermalysis

Membrane gelling

Transport processes so slow that growth cannot occur

Thermophile

Organism that grows best in high temperatures

Mesophile

Organism that grows best in moderate temperatures

How does temperature effect proteins?

Protein folding, and enzyme denaturation

What is the temperature “Danger Zone”?

Between 40 and 140 degrees farenheit

Psychrophile

Organism that grows best in permanently cold environments

Hyperthermophile

Organism that grows best in extremely hot environments

Which type of microbe based on temperatures for growth, cause diseases in humans?

Mesophiles

Neutrophile

Organisms that grow best in neutral pH environments

Acidophiles

Organisms that grow best in acidic environments

Alkaliphiles

Organisms that grow in basic pH environments

Osmotic pressure

The pressure exerted on a semipermeable membrane by a solution containing solutes that cannot freely cross membrane

Hypotonic

Lower solute concentration than cytoplasm, cell swells

Hypertonic

Greater solute concentration than cytoplasm, cell shrinks

Halophile

Organism that grows best in high salt concentrations

Haltolerature

Grows best in high salt concentrations, but can also grow in absence of salt

Nonhalophile

Organism that grows best in low salt concentrations

What structure helps prevent osmotic pressure?

Cell wall

Hydrostatic pressure

Water exerts pressure in proportion to its depth

Barophile

Organism that grows best under extreme pressure

Quantum sensing

Response to cell density

Inoculum

The sample

Culture medium

Any material used to grow bacteria

Culture

Act of cultivating, or the microorganisms that are cultivated

Axenic

Arising from a single progenitor, forms one colony

Aeseptic technique

Without contamination

What are the two most common isolation techniques?

Streak and pour plates

What are the 6 types of culturing media?

Defined, complex, selective, differential, anaerobic, and transport media

What kind of media is MacConkey?

Selective and differential

What kind of media is Blood agar?

Differential

Defined media

Known chemical composition

Complex media

Unknown chemical composition

Selective media

Allow growth of only the desired microbes

Differential media

Distinguishes among different organisms

Anaerobic media

No O2

Transport media

For clinical specimen

Binary fission

One cell divides into two cells

Bacterial cell divison

A logarithmic progression

What are fastidious bacteria?

Having complex growth requirements

What are capnophilic bacteria?

Organisms that grow best in elevated concentration of CO2

What are cell cultures used for?

Some obligate parasites and fastidious bacteria

What are enrichment cultures for?

Encourages the growth of a particular microorganism

What are candle jars used for in low-oxygen cultures?

To grow capnophilic bacteria

Which is each method below used for?

• Refrigeration

• Deep-freezing

• Lypophilization

Refrigeration: short term, Deep-freezing: years, Lypophilization: Decades-sublimation to remove water from a frozen culture by vacuum

Is bacterial growth linear or exponential?

Exponential

Formula to calculate the number of bacteria after n number of generations

total time/ generation time, then N0 × 2^n

Generation time

Time required for a bacterial cell to double

Starting with 1 bacterium, how many bacteria in your culture after 2 hours if the generation time is 30 minutes?

16

4 Phases of Bacterial Growth

Lag, log, stationary, and decline phase

Lag phase

Little or no change in number of cells, but metabolic activity is high

Exponential growth (log) phase

Bacteria multiply at the fastest rate possible under the conditions provided

Stationary phase

An equilibrium between cell division and death

Decline phase

Number of deaths exceeds the number of new cells formed

Direct methods to measuring microbial reproduction

Serial dilution and viable plate counts, membrane filtration, most probable number, microscopic counts, and electronic counters

Serial dilution and viable plate counts

Require incubation, counts only live cells

Membrane filtration

Recquire incubation, used for a very dilute sample and water samples

Most probable number

Requires incubation, based on statistical probability

Microscopic counts

No incubation, counts both live and dead cells

Indirect counts

No incubation, based on how cloudy growth media is

PCR (unculturable bacteria)

Amplify DNA by repeated rounds of DNA replication

Growth phase when population increases logarithmically

Exponential

Statistical estimation to enumerate bacteria

MPN

Drying by vacuum to remove water from a frozen sample

Lypophilization

Photoautotrophs

Light, CO2

Photoautotrophs

Use light and inorganic chemicals

Chemoautotrophs

Use chemical compounds and inorganic chemicals

Photoheterotrophs

Use light and organic chemicals