Microbio Lecture 4: Microbial Cell Growth, Development, and Control

Essential nutrients

Those that must be supplied from the environment.

Macronutrients

• Major elements in cell macromolecules (C, H, N, O, P, S)

• Cations necessary for protein function (Mg²⁺, Ca²⁺, Fe²⁺, K⁺)

Micronutrients

Trace elements necessary for enzyme function

• Co, Cu, Mn, Zn

Phototrophs

Obtain energy from chemical reactions triggered by light.

Chemotrophs

Obtain energy from oxidation-reduction reactions.

Lithotrophs

Use inorganic molecules as a source of electrons.

Organotrophs

Use organic molecules as a source of electrons.

Three aspects of naming a microbe based on their nutrient uptake

1. Energy source (chemo/photo)

2. Carbon source (hetero/auto)

3. Electron source (organo/litho)

Microbial energy sources

1. Photo (light)

2. Chemo (energy from breaking down chemical compounds)

Microbial carbon sources

1. Autotrophs (fix CO2 themselves from the environment, “auto” means self)

2. Heterotrophs (use carbon from organic molecules like sugars/amino acids)

Microbial electron sources

1. Organo- (source is organic molecules such as glucose)

2. Litho- (source is inorganic substances such as H2S, Ammonia)

Carbon Cycle

Essentially, autotrophs intake CO2 and produce C, while heterotrophs intake C and release CO2.

Three methods of microbial nutrient uptake

1. Permeases: the transporter that is substrate-specific.

2. Dedicated nutrient binding proteins (the grabber that brings compounds to the transporters—permeases).

3. Membrane-spanning protein channels/pores

Facilitated Diffusion

Helps solute move across a membrane from a region of high concentration to one of lower concentration.

• Does not use energy and cannot move a molecule against its gradient

Active transport

Works against the gradient, energy is required to complete active transport.

Two subdivisions of active transport

1. Symport

2. Antiport

Symport

Two molecules travel in the same direction.

Antiport

The actively transported molecule moves in the direction opposite to the driving ion.

• One molecule going down its concentration gradient releases the energy for another molecule to move against its concentration gradient.

Coupled transport systems

Energy released by a driving ion moving down its gradient is used to move a solute up its gradient.

ABC Transporters

ATP-Binding Cassette (ABC Superfamily), use ATP directly to transport nutrients.

Uptake ABC Transporters

Transport nutrients into the cell.

Efflux ABC Transporters

Transport nutrients out of the cell.

Siderophores

Specialized molecules secreted to bind ferric ion (FE3+) and transport it into the cell.

• They are like fishing hooks searching for iron and then they bring it back and release it into the cytoplasm.

Porins

Porin channels/pores that let small hydrophillic molecules through.

Aquaporins

Channels that let only water through down its gradient, no energy needed (facilitated diffusion).

Simple diffusion

Small, non-polar molecules that pass straight through the lipid bilayer from high to low concentration with no added energy.

Culture media for growing bacteria

1. Liquid/broth (studying pure cultures)

2. Solid, usually with agar (separating mixed cultures)

Types of Media for culturing bacteria

1. Complex Media

2. Minimal Defined Media

3. Enriched Media

4. Selective Media

5. Differential Media

Complex Media

Nutrient rich but poorly defined.

• Many different kinds of bacteria can grow, allowing for little to no distinction between bacterial strains.

• Most common type is Luria Bertani

Minimal Defined Media

Contain only those nutrients that are essential for growth of a given microbe.

• Most common type is M9 or Sulfur Oxidizers

Enriched Media

Complex media (nutrient rich) to which specific blood components are added.

Selective Media

Favor the growth of one organism over another.

Differential Media

Exploit differences between two species that grow equally well.

Growth Factors

Nutrients that a microbe needs but cannot make for itself.

• If a growth plate doesn’t have the growth factors a specific strain needs, it will not grow.

• Ex. Vitamin K, Cysteine, Glutamate, Alanine

How do most bacteria divide

Binary fission

Microbial Growth Cycle Phases

1. Lag Phase

2. Log Phase

3. Stationary Phase

4. Death Phase

Lag Phase

Bacteria are preparing their cell machinery for growth.

Log Phase

Growth approximates an exponential curve.

• Going through doubling at regular intervals.

Stationary Phase

Cells stop growing and shut down their growth machinery while turning on stress responses to retain viability.

Death Phase

Cells die with a “half-life” similar to that of radioactive decay, a negative exponential curve.

Generation Time

Varies depending on the species of microorganism and environmental conditions.

• Ranges from 10 minutes for some bacteria (like E. Coli) to days for some eukaryotes.

Biofilms

Bacteria form specialized, surface-attached communities.

• One or more species and can be found on organic or inorganic surfaces.

When are biofilms plentiful?

When nutrients are abundant.

• Once nutrients become scarce, individuals detach from the community to go forage for more nutrients.

What are biofilms made of

EPS: extracellular polymeric substance

• Microbes are protected within that environment.

• Nutrient exchanges between organisms are facilitated.

Quorum Sensing

Bacteria can communicate with eachother through chemical signals prior to creating an EPS biofilm, creating a complex channeled community that generate new planktonic cells.

When do cells create endospores

In response to environmental stresses.

• Nutrient depletion triggers an asymmetrical division, leading to a forespore that develops into a resistant endospore and later can germinate.

Which bacterial strains produce endospores

1. Clostridium

2. Bacillus

What are normal growth conditions for bacteria?

1. Sea level

2. 20-40 degrees celsius

3. Neutral pH

4. 0.9% salt and ample nutrients

Extremophile

Any organism whose ideal growing conditions are outside the normal bacterial growth range.

• Often an organism that is an extremophile for one environment factor is also an extremophile with respect to others as well.

Hyperthermophile

Able to grow in conditions above 80 degrees celsius.

Thermophile

Able to grow in conditions between 50-80 degrees celsius.

Mesophile

Growth in normal temperatures (15-45 degrees celsius)

Psychrophile

Able to grow in freezing conditions (below 15 degrees celsius)

Alkaliphile

Able to grow in basic conditions (above pH of 9)

Neutralophile

Grows at normal pH levels between 5 and 8

Acidophile

Grows best in acidic conditions (below pH of 3)

Halophile

Growth in high salt concentrations

Halotolerant

High salt not required for growth, but is tolerant.

Aerobe

Can only grow with abundant oxygen.

• Use molecular oxygen as a terminal electron acceptor in the electron transport system (aerobic respiration).

Facultative anaerobes

Can grow with or without oxygen.

• Possess the ability to do both fermentative metabolism and aerobic respiration.

Microaerophile

Can only withstand small amounts of oxygen to grow.

Strict anaerobe

Can only grow in conditions without oxygen.

• ROS: reactive oxygen species

Barophile

Can only grow in high pressure environments.

Barotolerant

Can grow in pressures ranging from 10 to 500 atm.

Why are high temperatures potentially harmful for bacteria that grow in normal-cold temperatures?

Enzyme denaturation

Why are low temperatures potentially harmful for bacteria that grow in normal to hot temperatures?

Decrease in membrane fluidity and enzymatic activity.

What pH do most fungi prefer?

An acidic pH between 4 to 6.

How do microorganisms modify in response to external pH changes?

Neutrophiles exchange potassium for protons.

Water activity (aw)

A measure of how much water is available to use.

Osmolarity

A measure of the number of solute molecules in a solution and is inversely related to water activity (aw)

Aerotolerant anaerobes

Grow in oxygen while retaining a fermentation-based metabolism.

Sterilization

Killing all living cells, spores, and viruses

Disinfection

Killing or removal of pathogens from inanimate objects, does not necessarily result in sterilization.

Antisepsis

Killing or removal of pathogens from the surface of living tissues.

Sanitation

Reducing the microbial population to safe levels.

Physical agents that kill microbes

• Boiling water kills most cells (moist heat is more effective than dry heat)

• Low temperatures (refrigeration)

• Filtration

• Irradiation (UV light, Gamma rays, electron beams, X-Rays)

How are antibiotics classified

According to their mode of action

• Some target cell wall synthesis/cell membrane structure

• Some attack protein synthesis

• Some attack DNA replication

Penicillin

Mimics a part of the cell wall, preventing peptidoglycan synthesis and preventing cell wall formation.

Biocontrol

The use of one microbe to control the growth of another.

Probiotics

Contain certain microbes that when ingested, aim to restore balance to intestinal flora.

Phage Therapy

Treats infectious diseases with a virus targeted to the pathogen.