Module 6.1 Microbial Growth

Define macronutrient and provide examples

Needed in large amounts to provide energy & build physical structures

ex → carbohydrates, proteins, lipids, water

Define micronutrients and provide examples

Needed in small/trace amounts to support metabolism, immunity, & enzyme function (cofactors)

ex → vitamins, minerals (fe, ca, k, mg, zn)

Define phototroph (energy source)

Energy from light (photosynthesis)

Define chemotroph (energy source)

Energy from chemical compounds

Define autotroph (carbon source)

Uses inorganic CO2 as carbon source (can use CO2 to build organic molecules)

Define heterotroph (carbon source)

Requires organic carbon

Define Photoautotroph with regard to carbon and energy sources

Use light for energy to make sugar from CO2 (have chloroplasts like plants)

ex → cyanobacteria: microcoleus chthonoplastes

Define Chemoautotroph with regard to carbon and energy sources

Use chemicals for energy and inorganic CO2 as a carbon source

ex → methanogens: methanobrevibacter intestini

Define Photoheterotroph with regard to carbon and energy sources

Use light for energy and organic compounds as carbon sources

ex → purple photosynthetic bacteria: rhodospirillum rubrum

Define Chemoheterotroph with regard to carbon and energy sources

Use chemicals for energy and organic compounds as carbon sources (cellular resp & fermentation)

ex → staphylococcus aureus

Saprobe

Chemoheterotroph

Feeds on organic material from dead organisms

ex → decomposers - fungi

Parasite

Chemoheterotrophs

Feed on cells or tissues form living organisms; cause harm to host!

• Can be viruses, bacteria, fungi, protozoa, or helminths

• Ectoparasites – live on host 

• Endoparasites – live in host

• Obligate parasites – unable to reproduce outside of a living host

ex → Mycobacterium leprae (leprosy bacillus)

Which gas is important for autotroph metabolism?

CO2

Which gas is important for aerobic respiration?

O2 (potentially toxic oxidizing agent)

Why is oxygen toxic to some organisms?

Can be converted into reactive oxygen species (ROS) that can oxidize macromolecules

Reactive Oxygen Species (ROS)

Can damage DNA, RNA, lipids, amino acids, coenzymes, etc

• Singlet oxygen (O) extremely reactive

• Superoxide ion (O2-) highly reactive

• Hydrogen peroxide (H₂O₂) – toxic to cells

• Hydroxyl radical (OH^-) – highly reactive

Oxidation

Loss of electrons, hydrogen, & gain of oxygen

Obligate aerobe

Require O2 & can detoxify ROS with enzymes, produce ATP thru aerobic cellular resp.

ex → Mycobacterium tuberculosis & Bacillus

Microaerophile

Requires a small amount of O2 but harmed by levels in atmosphere, lives in soil or animal host, may perform aerobic cellular resp or fermentation

ex → Helicobacter pylori

Facultative anaerobe

Can use O2 when present, but doesn’t need it

Produce ATP thru aerobic cellular resp (when O2 available) & anaerobic respiration/fermentation if O2 not present

ex → E.coli, staphylococcus, salmonella, listeria

Aerotolerant anaerobe

Doesn’t use O2 but can survive around it, can detoxify oxygen species

ex → lactobacillus

Obligate anaerobe

Can’t use O2 & detoxify ROS, lack enzyme to detoxify and use oxygen

ex → many oral & intestinal bacteria

Lab connection: What does the catalase test tell you about an organism?

Determines whether organisms has enzyme catalase which detoxifies H2O2

A - Identify the growth pattern for obligate aerobes, obligate anaerobes, facultative anaerobes, microaerophiles, and aerotolerant anaerobes in the image below. (Growth in thioglycolate media (FTM))

Obligate aerobes

B - Identify the growth pattern for obligate aerobes, obligate anaerobes, facultative anaerobes, microaerophiles, and aerotolerant anaerobes in the image below. (Growth in thioglycolate media (FTM))

Obligate anaerobes

C - Identify the growth pattern for obligate aerobes, obligate anaerobes, facultative anaerobes, microaerophiles, and aerotolerant anaerobes in the image below. (Growth in thioglycolate media (FTM))

Facultative anaerobics

D - Identify the growth pattern for obligate aerobes, obligate anaerobes, facultative anaerobes, microaerophiles, and aerotolerant anaerobes in the image below. (Growth in thioglycolate media (FTM))

Microaerophiles

E - Identify the growth pattern for obligate aerobes, obligate anaerobes, facultative anaerobes, microaerophiles, and aerotolerant anaerobes in the image below. (Growth in thioglycolate media (FTM))

Aerotolerant anaerobes

Why is temperature an important parameter for microbial growth?

• Minimum growth temperature – lowest temperature at which a given species will grow, below → too cold = metabolism stops/slows

• Maximum growth temperature – highest temperature at which a given species will grow, above → too hot = proteins denature and the organism dies

• Optimum temperature range = temp at which a given species grows the best/fastest

Define Psychrophile with regard to growth optimum temperature range

Cold-loving

• Optimum temp < 15°C

• No growth > 20°C

• Grow freely in refrigerator (4°C)

• Rarely pathogenic, will denature if temp is high

Define Psychrotroph with regard to growth optimum temperature range

Cold tolerant

• Optimum temp 15-30°C

• Slow growth in low temps

• Some can cause food-borne illness

ex → Listeria monocytogenes - grows rapidly at refrigeration temps

Listeriosis

Psychotroph

Top 3 causes Food-borne illness/related deaths

Symptoms: fever, muscle aches, GI symptoms, sepsis (invasive infection)

• Elderly and immunocompromised present with septicemia and meningitis

• Pregnant women may experience a fever and other non-specific symptoms, such as fatigue and aches, followed by fetal loss or bacteremia and meningitis in their newborns

Mesophiles

Moderate-loving

Optimum temp range 20 - 40°C

• Human pathogens opt temp 30-40°C

Medically significant

• Inhabit animals, plants, soils, water

• Can survive in temperate, tropical, subtropical regions

ex → Staphylococcus aureus

Thermophiles

• Heat-loving

• Optimum temp 45°C - 80°C, most euk cant survive above 60°c

• Found in soil & water w/ volcanic activity, hot springs, compost piles, direct sun exposure

ex → Thermus aquaticus

Hyperthermophiles

• aka extreme thermophiles

• Optimum 80 - 121°C – Some can survive boiling water!

ex → archaeon Geogemma barossii which can survive up to 2 hours as 130°C

Why are many human pathogens mesophiles?

They thrive at human’s optimum temp of 37°C and a pH around 7.4 (human optimum pH)

What is an acidophile?

Organism that grows best in acidic environments (low pH)

What is the optimum pH range for acidophiles?

Usually pH 0–5.5

What is a neutrophile?

An organism that grows best at a neutral pH.

What is the optimum pH range for neutrophiles?

Approximately pH 5.5-8.0

Whats an example of a neutrohphilic bacterium

E.coli

What is an alkaliphile?

An organism that grows best in alkaline (basic) environments.

What is the optimum pH range for alkaliphiles?

Approximately pH of 8.5-11.5

Give an example of an alkaliphilic bacterium.

Bacillus alcalophilus

Which pH-loving organisms are most likely to be human pathogens?

Neutrophiles, because they grow best at the pH found inside the human body. (pH of 7.0-7.4)

Why are acids sometimes added to food as preservatives?

To lower the pH and inhibit microbial growth, preventing food spoilage and extending shelf life.

Define osmosis

Water moves from high water (low solute) to low water (high solute) concentration

Define tonicity

• Ability of a surrounding solution to cause a cell to gain or lose water

• Describes concentration of solutes (although water is moving)

Define isotonic

Same solute concentration

1% sol out/in, 99% water out/in

• water moves back in forth equally = dynamic equilibrium

ex → humans

Define hypotonic

Lower solute concentration

1% sol in, 99% water in (goes out) → 10% sol out, 90% out

Swell & burst = lysis

Define hypertonic

Higher solute concentration

1% water in, 99% sol in →

Shrink & crinkle = crenation

Define osmotic pressure

External pressure that must be applied to stop inward flow of water across a semipermeable membrane

What are osmophiles?

Can survive in environments with high osmotic pressure (solute concentrations)

• many are yeasts

• protect themselves against dehydration by synthesizing compatible solutes or osmoprotectants (like specific amino acids & alcohols)

• can cause spoilage of sugar foods/drinks

ex → some saccharomyces species

What are halophiles?

Organisms that grow at high salt concentrations

What are obligate halophiles?

Require high salt concentrations to survive

What are facultative halophiles? Provide an example

Can tolerate salt concentrations higher than normal (sometimes up to 10-15%)

ex → S. aureus

Why is mannitol salt agar (MSA) differential?

Contains sugar mannitol and pH indicator phenol red

• organisms ferments mannitol & produces an acid = lowers pH & changes red/pink to yellow

Why is mannitol salt agar (MSA) selective?

Contains 7.5% NaCl which stops growth of most Gram-negative bacteria & nonstaphylococcal organisms, but allows salt-tolerant staphylococcal species to grow

What species do we use MSA to identify in lab?

S.aureus

What are barophiles?

Organisms that can survive in high pressure environments like deep ocean

• evolved waxy cell layer = protects against crushing pressures & frigid temps

• explode under normal atm conditions

ex → barophile Halomonas salaria