Growth L6

What does microbial growth refer to

An increase in the number of cells, not the size of individual cells

What are the two types of requirements bacteria need for growth

Chemical requirements and physical requirements

What are the four main chemical requirements for bacterial growth

Carbon, N/P/S and other nutrients, oxygen, and organic growth factors

What are the three main physical requirements for bacterial growth

Temperature, pH, and osmotic pressure

Why is carbon required by bacteria

Carbon is required to build all organic compounds

Where do chemoheterotrophs obtain their carbon

From the same organic molecules they use as an energy source

Where do photoautotrophs and chemoautotrophs obtain their carbon

From inorganic carbon in the environment

What are macronutrients

Nutrients required in relatively large amounts for bacterial growth

What are the main macronutrients bacteria require

O, H, N, S, P, C, K, Ca, Mg, and Fe

What is the difference between macronutrients and micronutrients

Macronutrients are needed in large amounts; micronutrients are needed in trace amounts

What roles can K, Ca, Mg, and Fe play in bacteria

They are cations that can act as enzyme cofactors and help stabilize membranes

What are the six micronutrients listed in the lecture

Mn, Zn, Co, Mo, Ni, and Cu

Why are micronutrients called trace elements

They are required by bacteria in very small amounts

How are micronutrients often supplied to bacteria

They are often supplied through water or components of the growth medium

What are micronutrients commonly used for

They serve as parts of enzymes and cofactors

Do all microbes require exactly the same nutrients

No. Some microbes require unique substances, such as silicic acid in diatoms

What are the five categories of bacterial oxygen tolerance

Obligate aerobes, obligate anaerobes, facultative anaerobes, microaerophiles, and aerotolerant anaerobes

Why can oxygen be dangerous to some bacteria

Oxygen produces highly reactive metabolic by-products that can damage cells

What allows bacteria to tolerate oxygen

They must have enzymes that break down harmful oxygen by-products

Which two enzymes are important for oxygen tolerance

Superoxide dismutase (SOD) and catalase

What are examples of organic growth factors

Amino acids, vitamins, purines, and pyrimidines

Why do bacteria need growth factors

They need them when they cannot synthesize these essential organic compounds themselves

Do all bacteria require the same growth factors

No. The required growth factors vary between different types of bacteria

What are cardinal growth temperatures

The minimum, optimum, and maximum temperatures at which an organism can grow

Can bacteria grow outside their optimum temperature

Yes, but their growth rate is reduced

Why is temperature important for bacterial growth

Temperature affects membrane viscosity and enzyme activity, which affect cell functions

What are psychrophiles

Microorganisms that have an optimum growth temperature of about 4°C

What temperature range can mesophiles grow between

About 10°C to 50°C

What are mesophiles commonly associated with

Most common microbial spoilage and many pathogens

What temperature range can thermophiles grow between

About 40°C to 75°C

What is a key molecular adaptation of psychrophiles to cold temperatures

Their enzymes have greater flexibility, allowing them to function at low temperatures

How are psychrophile membranes adapted to cold temperatures

They contain more polyunsaturated and shorter-chain fatty acids to maintain membrane flexibility

What are cold shock proteins

Proteins that help protect cellular proteins during exposure to cold temperatures

What are cryoprotectants

Substances such as glycerol or sugars that prevent damaging ice crystal formation

Does freezing necessarily kill microbial cells

No. Freezing can stop microbial growth without killing the cells

How are enzymes and proteins of thermophiles adapted to high temperatures

They are more heat-stable and contain structural features that increase stability

What type of bonds can help thermophile proteins remain stable at high temperatures

More ionic bonds between basic and acidic amino acids

How are thermophile membranes adapted to high temperatures

They have increased saturated fatty acids, which help maintain membrane stability

What are heat shock proteins

Proteins that help protect and stabilize cellular proteins during high temperatures

How are archaeal membranes adapted to extreme heat

They use repeating isoprene units and can form a lipid monolayer, increasing stability

What are the three main pH categories of microorganisms

Acidophiles, neutrophiles, and alkaliphiles

What pH do acidophiles grow best at

Below pH 5.5

What pH do neutrophiles grow best at

Between pH 5.5 and 8.0

What pH do alkaliphiles grow best at

Above pH 8.0

Why do microorganisms have a specific optimum pH

Their cellular components, such as enzymes and membranes, function best at that pH

Is the internal pH of most bacterial cells the same as their preferred environmental pH

No. Their internal pH is usually near neutral

Why is maintaining the correct water balance important for bacteria

Bacteria need water to obtain dissolved nutrients and maintain normal cell functions

What happens to a bacterial cell in a hypotonic environment

Water enters the cell, but the cell wall usually prevents it from bursting

What happens to a bacterial cell in a hypertonic environment

Water leaves the cell, causing the plasma membrane to shrink away from the cell wall. The loss of water means the cell also loses nutrients

What is plasmolysis

The shrinking of the plasma membrane away from the cell wall due to water loss

What is a nonhalophile

A microorganism that cannot tolerate high concentrations of salt

What is a halotolerant microorganism

A microorganism that can tolerate higher salt concentrations but does not require salt for growth

What is a halophile

A microorganism that requires salt for growth

What is an extreme halophile

A microorganism that requires very high concentrations of salt for growth

Why can high salt concentrations affect bacterial growth

They cause water to leave the cell, disrupting water balance and nutrient availability

Where do many microorganisms grow in nature instead of freely suspended in liquid

They often grow attached to surfaces in biofilms

What is a biofilm

A community of microorganisms attached to a surface and enclosed in a complex protective matrix

Why are broth cultures not always representative of how microbes grow in nature

Many microbes naturally grow attached to surfaces in biofilms rather than freely suspended in liquid

What is a growth medium

A nutrient-containing material used to provide bacteria with the conditions needed for growth

What is an inoculum

The bacteria introduced into a growth medium to start a culture

What are the two physical forms of bacterial growth media

Solid and liquid

What is agar

A complex polysaccharide used as a solidifying agent in growth media

Why is agar useful for growing bacteria

It can solidify the growth medium without being metabolized by many microorganisms

At what temperature is agar liquid

About 100°C

At what temperature does agar become solid

About 40°C

What is a chemically defined medium

A growth medium in which the exact chemical components and amounts are known

Why are chemically defined media useful

They can be specifically tailored to provide the requirements of a particular microorganism

What is a disadvantage of chemically defined media

They can be complicated and time-consuming to prepare

What is a complex medium

A growth medium made from extracts or digests of materials such as yeast, meat, or plants

Why are the exact amounts of nutrients in complex media not known

The composition of the extracts or digests is not precisely known and can vary between batches

What are common examples of complex media

Nutrient agar and nutrient broth

What is the difference between selective and differential media

Selective media allow some microorganisms to grow while preventing others; differential media distinguish microorganisms based on characteristics such as growth, color, or appearance

What is selective media used for

To allow certain microorganisms to grow while preventing others from growing

What is differential media used for

To distinguish or identify microorganisms based on differences in growth, color, or appearance

What is Mannitol Salt Agar (MSA)

A medium that is both selective and differential

Why is Mannitol Salt Agar selective

Its high salt concentration allows Staphylococcus and other salt-tolerant microorganisms to grow while inhibiting many other bacteria

Why is Mannitol Salt Agar differential

It differentiates bacteria based on whether they can ferment mannitol

What is blood agar used for

It is a differential medium used to distinguish bacteria based on hemolysis

What are the three types of hemolysis seen on blood agar

Beta hemolysis, alpha hemolysis, and gamma hemolysis

What is beta hemolysis

Complete destruction of red blood cells around the bacterial growth

What is alpha hemolysis

Partial destruction of red blood cells around the bacterial growth

What is gamma hemolysis

No hemolysis of red blood cells

What are the basic requirements for culturing bacteria in the laboratory

Bacteria need a suitable temperature, pH, osmotic pressure, chemical nutrients, and oxygen conditions

How can the correct temperature for bacterial growth be provided in the laboratory

Using equipment such as an incubator or refrigerator

How can the correct pH and osmotic conditions be provided in a growth medium

By using buffers and adding the appropriate chemicals

How can the chemical requirements of bacteria be provided in a growth medium

By supplying the necessary nutrients and other required chemicals

Why are aerobic bacteria generally easier to culture than anaerobic bacteria

Oxygen is readily available for aerobic bacteria, while anaerobic bacteria require oxygen-free conditions

How can anaerobic bacteria be cultured in the laboratory

Using reducing media, anaerobic jars, or anaerobic chambers

Why are special methods needed to culture anaerobic bacteria

They cannot tolerate oxygen, so oxygen must be removed or prevented from reaching the culture

What is an anaerobic jar used for

It creates an environment without oxygen so anaerobic bacteria can grow

What is an anaerobic chamber or glove box used for

It allows anaerobic cultures to be handled and maintained in an oxygen-free environment

What are the basic steps for culturing bacteria in the laboratory

Provide the required nutrients and physical conditions, sterilize the growth medium, and introduce the bacteria using an inoculum