MB lectures 5-6

Name 2 classes of essential nutrients for microbes.

Macronutrients, micronutrient

Name 2 types of macronutrients

Major elements in cell macromolecules(C, O, H)

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

How do autotrophs acquire carbon?

They fix carbon dioxide and assemble into organic molecules (mainly sugars).

How do heterotrophs acquire carbon?

Use preformed organic molecules(through eating)

This class of organisms obtain energy from chemical reactions triggered by light.

Phototrophs

This class of organisms obtain energy from redox reactions.

Chemotrophs

This class of organisms use inorganic molecules as a source of electrons.

Lithotrophs

This class of organisms use organic molecules as an energy source.

Organotrophs

Name 2 ways that material passes through membranes that don’t require energy.

Passive diffusion and facilitated diffusion

What materials can pass through the plasma membrane through passive diffusion?

Gases, small hydrophobic molecules, small uncharged polar molecules(like water)

Name an example of facilitated diffusion.

Glycerol transporter

Name 3 classes of active transport systems.

Simple transport, group translocation, the ABC system

Describe simple transport.

Driven by the energy in the proton motive force.

What is symporters?

The molecules travel in the same direction. One of the molecules travels down its gradient, which drives another molecule to travel against its gradient.

What is antiport?

Two molecules travel in opposite directions. One of the molecules travels down its gradient, which drives another molecule to travel against its gradient.

The ATP-binding cassette superfamily uses _____ energy to transport material against its gradient.

ATP

The phosphotransferase System (PTS) uses energy from _______ to pass material into cell, the ________ the material as it enters the cell.

Phosphoenolpyruvate(PEP); modifies

Which proteins in the Phosphotransferase system (PTS) differ based on the type of sugar being transported?

Enzyme 2A/B/C

Which proteins in the Phosphotransferase system (PTS) are the same no matter which sugar is transported?

E1 and HPr

What are some benefits of using liquid media to culture bacteria?

Useful for studying the growth characteristics of a pure culture, can add things into the medium

What are some benefits of using solid media to culture bacteria?

Useful for trying to separate mixed cultures from clinical specimens or natural environments

What are 2 main techniques for isolating pure colonies?

Dilution streaking and spread plate

What is dilution streaking?

Use a loop to drag bacteria across an agar plate. flame the loop to sterilize it, then drag the loop through the edge of the previous section and spread them into the next quadrant. Repeat until all quadrants are filled, flaming the loop between each streak.

What is the spread plate technique?

Tenfold serial dilutions are performed on a liquid culture. A small amount of each dilution is then plated so that there are a countable amount of colonies on the plate.

What is complex media?

Enriched media with an unknown composition. Autotrophs and phototrophs will grow on this

What is defined media?

Synthetic media where all constituents are known. Only phototrophs will grow on this, unless supplemented.

What is selective media?

Favors growth of particular microorganisms while inhibiting growth of others

What is differential media?

used to distinguish and identify particular types of microbes based on their biological characteristics

How is MacConkey Agar medium selective?

Only gram - bacteria grow on it.

How is MacConkey Agar medium differential?

only lactose fermenters will turn red

Describe the direct count method of counting bacteria.

Cells are counted directly under a hemocytometer chamber

Name some pros and cons to directly counting bacteria(using hemocytometer)

Pros: Accurate, fast

Cons: cannot tell if cells are alive or dead(can use a live/dead stain to distinguish)

Describe the viable plate count method of counting bacteria.

Incubates colonies and counts only cells able to reproduce

Name some pros and cons to the viable plate count method.

Pros: Counts only live cells

Cons: Requires time to form colonies

Describe the optical density(turbidimetric) method of counting bacteria.

Uses a spectrophotometer to measure the density of a solution of bacteria

Name the pros and cons to the optical density(turbidimetric) method of counting bacteria.

Pros: Super fast

Cons: Can’t tell if cells are alive or dead

Solution must be at 10⁷ – 10¹⁰ cells/ml

What is binary fission?

When mother cell splits into 2 identical daughter cells

What is generation time?

The time it takes for a population to double

What is the formula for the generation time for cells undergoing binary fission? Identify what each variable stands for.

N_t = N₀ × 2ⁿ

N_t = final cell number

N₀ =original cell number

n= number of generations

Name the 4 phases of the bacteria growth cycle in order.

Lag, Log, stationary, death

What is the simplest way to model the effects of a changing environment in bacteria growth?

Culture bacteria in a batch culture, which is a liquid medium within a closed system

What occurs during the lag phase?

Bacteria are preparing their cell machinery for growth. No division occurs during this phase.

Name 3 reasons for a lag phase.

1. The culture is older and requires a longer lag phase

2. Cells shifted from complex rich media to defined media need to synthesize new enzymes

3. Enzyme synthesis occurs to acclimate cells to change in pH or aeration

What types of cultures typically don’t need a lag phase?

Inoculum from an exponential phase culture

What occurs during the exponential phase?

Bacteria grows exponentially

What occurs during the stationary phase?

Cells stop growing while turning on genes for survival and maintenance. Cells often become smaller and reduce the number of ribosomes. Sporulation is common.

Name 3 reasons for the stationary phase

1. Substrate limitation in minimal, defined media.

2. Waste build up

3. O2 limitation in complex media due to high respiration rates and low solubility of O2

What occurs during the death phase?

Cell numbers decline, the extent of which is highly variable and not predictable.

What machine keeps a colony at a continuous, constant growth rate?

Chemostat

What is a biofilm?

A community of single or multiple species of microorganisms that stick to each other and a surface.

Cells in a biofilm become more tolerant to:

Antibiotics and disinfectants

How do cells signal to one another in a biofilm?

Quorum sensing

Name 2 conditions in which biofilms form.

When nutrients are plentiful, when bacteria are cued by environmental signals

What are endospores and why do they form?

A dormant, dehydrated core containing DNA and ribosomes produced by gram + bacteria during periods of nutrient starvation or environmental stress.