physiology and growth

What are the four requirements for life?

Liquid water; Carbon; Nutrients; Free energy

What is the main role of carbon in cells?

Backbone of organic molecules

What are growth factors?

Organic molecules cells cannot synthesize

Difference between defined and complex media?

Defined = known composition; Complex = unknown composition

What does blood agar test?

Hemolysis of red blood cells

What is MacConkey agar used for?

Selecting Gram-negative bacteria and detecting lactose fermentation

What is enrichment culture?

Method that favors growth of a specific organism

What is direct isolation?

Obtaining a pure culture from a single colony

What is a streak plate used for?

Isolating individual colonies

What does one colony represent?

A colony-forming unit (CFU)

Main limitation of microscopic counts?

Counts both live and dead cells

What is serial dilution?

Stepwise dilution to reduce cell concentration

What is the Great Plate Anomaly?

Most microbes cannot be cultured, so counts are lower than actual

What does spectrophotometry measure?
Why is a standard curve needed in spectrophotometry?
What affects turbidity measurements?

Turbidity (optical density)

To convert turbidity to cell number

Cell shape and light wavelength

Why is carbon essential for cells?

Carbon forms the backbone of all organic molecules including proteins, lipids, carbohydrates, and nucleic acids

List the six universally required macronutrients.

Carbon (C), Oxygen (O), Nitrogen (N), Hydrogen (H), Phosphorus (P), Sulfur (S)

What are growth factors?
Give examples of growth factors.

Organic molecules that a cell cannot synthesize and must obtain from its environment

Vitamins, amino acids, purines, and pyrimidines

What makes MacConkey agar selective?
What makes MacConkey agar differential?

Crystal violet and bile salts inhibit Gram-positive bacteria

A pH indicator changes color when lactose is fermented

What is binary fission?

A form of reproduction where one cell divides into two identical cells

What is the main equation for exponential growth?
What does Nt represent?
What does N0 represent?

Nt = N0 × 2^n

Number of cells at time t

How do you calculate number of generations (n) using natural log?

n = (ln Nt − ln N0) / 0.693

How do you calculate number of generations (n) using log base 10?

n = (log Nt − log N0) / 0.301

What does 0.693 represent in growth equations?

ln(2), because cells double each generation

What does 0.301 represent in growth equations?

log10(2), used when using base-10 logs

How do you calculate generation time?

g = t / n

How is division rate calculated?

D = 1 / g

What is a chemostat?

A continuous culture system where fresh medium is added and culture is removed at the same rate

How is growth rate controlled in a chemostat?
How is growth yield controlled in a chemostat?

By the dilution rate (rate of medium addition/removal)

By the concentration of the limiting nutrient

Why can exponential growth be maintained in a chemostat?

Because nutrients are continuously supplied and waste is removed

What is a key limitation of batch culture?

You cannot independently control growth rate and yield over time

What happens if doubling time decreases slightly?

Population size increases dramatically due to exponential growth

What are mesophiles?

→ Microbes with moderate temperature optima (~20–45°C), including human-associated microbes

What are psychrophiles?

→ Cold-loving microbes with optimal growth below 20°C

What are thermophiles?

→ Heat-loving microbes with optimal growth above 45°C

What are hyperthermophiles?

→ Microbes with optimal growth above 80°C

Why do high temperatures kill microbes?
Why do low temperatures slow microbial growth?

→ Proteins denature and lose function

→ Enzymes become less active and membranes become rigid

How do psychrophiles adapt to cold?

→ More unsaturated fatty acids and flexible proteins to maintain fluidity

How do thermophiles adapt to heat?

→ More stable proteins and saturated lipids to prevent denaturation

What type of fatty acids increase membrane fluidity?
What type of fatty acids increase membrane stability?

What type of fatty acids increase membrane fluidity?
→ Unsaturated fatty acids

What type of fatty acids increase membrane stability?
→ Saturated fatty acids

Why are archaeal membranes stable at high temperatures?

→ They can have lipid monolayers and isoprene chains

What is pH?
How does pH affect microbes?

→ pH = −log[H⁺], a measure of acidity

→ Impacts enzyme activity, membrane stability, and transport

How low can cytoplasmic pH go in acidophiles?
How high can cytoplasmic pH go in alkaliphiles?

→ ~4.6

→ ~9.5

What is water activity (aw)?

→ The availability of water for microbial use (range 0–1)

What does aw = 1 mean?

→ Pure water

How do solutes affect water activity?

→ They lower it by binding water

Why does low water activity inhibit growth?

→ Water is unavailable for cellular processes

What happens in a hypotonic environment?
What happens in a hypertonic environment?

→ Water enters the cell

→ Water leaves the cell (cell shrinks/plasmolysis)

What are compatible solutes?

→ Molecules that balance osmotic pressure without interfering with cell function

Why are compatible solutes important?
Do compatible solutes disrupt metabolism?

→ They prevent water loss in high-solute environments

Do compatible solutes disrupt metabolism?
→ No

Why is oxygen toxic to some microbes?
What are reactive oxygen species (ROS)?

→ It forms reactive oxygen species (ROS)

→ Highly reactive molecules that damage cells

aerobes, microaeriphiles , facultative anaerobes, aerotolerant anaerobes , obligate anaerobes?

What are aerobes?
→ Require oxygen to grow

What are microaerophiles?
→ Require low oxygen levels (0.5–5%)

What are facultative anaerobes?
→ Can grow with or without oxygen

What are aerotolerant anaerobes?
→ Do not use oxygen but can tolerate it

What are obligate anaerobes?
→ Killed by oxygen

How do microbes survive oxygen exposure?
What does catalase do?

→ They use enzymes to detoxify ROS

→ Breaks down hydrogen peroxide (H₂O₂)

How can you grow anaerobic microbes in the lab?

→ Remove oxygen using reducing agents or anaerobic chambers

What are reducing agents?

→ Chemicals that remove oxygen (e.g., thioglycolate)

Facultative anaerobe vs aerotolerant anaerobe

→ Facultative: uses O₂ if present
→ Aerotolerant: ignores O₂, never uses it

Why does adding salt or sugar preserve food?

→ Lowers water activity

What limits life at high temperatures?

→ Protein and membrane stability

What is the main survival strategy in high solute environments?

→ Compatible solutes

What are the main approaches to control microbial growth?

→ Sterilization, chemical control, antibiotics, food preservation

What is sterilization? What is required for something to be considered sterile?
most common method ?

→ Complete removal of ALL microbes, including endospores

→ No living microorganisms remain

heat = most common method

What device is used for heat sterilization?
what does it use to sterilize and what are standard conditions.

autoclave

What does an autoclave use to sterilize?
→ Steam under pressure

What are standard autoclave conditions?
→ 121°C for at least 20 minutes

What actually kills microbes in an autoclave?
→ High temperature (not pressure)

What is decimal reduction time (D-value)?
What does a high D-value indicate?
Which microbes have the highest heat resistance?

→ Time required to reduce a population by 90% (1 log)

higher value indicated resistance to heat

endospores have highest resistance

What is pasteurization?
Does pasteurization sterilize?

What is pasteurization?
→ Controlled heating to reduce microbial load in liquids

Does pasteurization sterilize?
→ No

Why is pasteurization used?
→ To make food safer without damaging quality

What types of radiation are used to control microbes?
which penetrate deeply, what is a limitation of UV light /

What types of radiation are used to control microbes?
→ Gamma rays, X-rays, UV light

Which radiation penetrates deeply?
→ Gamma rays and X-rays

What is a limitation of UV light?
→ Poor penetration (only works on surfaces)

What are examples of chemical sterilants?
→ Bleach, formaldehyde, ethylene oxide gas

→ Bleach, formaldehyde, ethylene oxide gas

→ Sterilizing heat-sensitive medical equipment

sterilants vs disinfectants vs antiseptics

What are sterilants?
→ Kill all microbes, including endospores

What are disinfectants?
→ Kill most microbes but not endospores (used on surfaces)

What are antiseptics?
→ Kill microbes and are safe for living tissue

→ Sterilants > Disinfectants > Antiseptics

what are antibiotics and do they work on viruses

What are antibiotics?
→ Antimicrobial drugs used to treat bacterial infections

Do antibiotics work on viruses?
→ No

What are the major targets of antibiotics?
Can antibiotics be bacteriostatic or bacteriocidal?

→ Cell wall synthesis, protein synthesis, DNA replication, folate synthesis, transcription, cell membrane

yes

What is hot holding?
What is canning?

→ Keeping food above 57°C to prevent growth

→ Heating food and sealing it to prevent contamination

Is removing oxygen enough to prevent microbial growth? why ?

Is removing oxygen enough to prevent microbial growth?
→ No

Why is oxygen removal unreliable?
→ Some microbes grow without oxygen

What is irradiation used for in food?

→ Killing microbes using radiation

Examples of chemical preservatives
What does smoking food do?

Examples of chemical preservatives
→ Nitrites, nitrates, sulfites

What does smoking food do?
→ Dries food and adds antimicrobial chemicals