BIOL 251 Microbiology Week 7 Lecture Notes

Microbiology: An Introduction 13th Edition - Chapter 6

Binary fission

The mechanism for cell replication

Generation time

Time required for a population of microbial cells to double

Fts proteins

Proteins essential for cell division in prokaryotes

MreB proteins

Proteins essential in shape-determining in prokaryotes

pH, temperature, osmotic pressure

What are some physical requirements for cell growth?

Carbon, nitrogen, sulfur, phosphorus, trace elements, oxygen, organic growth factor

What are some chemical requirements for cell growth?

optimum, minimum, maximum

What are the 3 temperature requirements for cell division?

Psychrophiles

Thrive in extremely cold temperatures, typically below 15°C.

Psychrotrophs

Can grow at low temperatures (0–30°C) but prefer moderate conditions.

Cause food spoilage

Mesophiles

Grow best at moderate temperatures, typically between 10–50°C.

Optimum temp 25-40°C

Most common type

Thermophiles

Thrive in high temperatures, usually between 40–70°C.

Optimum temp 50°C

Hyperthermophiles

Grow optimally at extremely high temperatures, often above 80°C.

65-110°C, optimum temp 85-105°C

Enzymes, proteins

stronger

cytoplasmic

Adaptations in extremophiles

1. _____ and _____ that withstand extreme low or high temps

2. More _____ chemical bonds between compounds

3. Modifications in _____ membrane

Acidophiles

Alkaliphiles

pH

Most bacteria - 6.5-7.5

Molds and yeasts - 5-6

_____: Grow in less than 6 pH

_____: Grow in more than 9 pH

Water

What is the most important requirement for growth?

Osmotic pressure

The pressure needed to stop the movement of water across a membrane

Plasmolysis

Hypertonic environments cause _____

The process of a cell shrinking due to water loss

Halophiles

Halotolerant

Osmophiles

Xerophiles

Osmotic Effects on Microbial Growth

_____: Have a specific requirement for NaCL

Extreme or Obligate Halophiles: Require high NaCl levels for growth (15-30%)

_____ or Facultative Halophiles: Can tolerate high salt content, but only need small amounts (2%) for growth

_____: Live in high sugar environments

_____: Live in very dry environments

Obligate

Facultative

Obligate

Aerotolerant

Micro

The Effect of Oxygen on Microbial Growth

_____ Aerobes: Require oxygen to grow and use it for aerobic respiration.

_____ Anaerobes: Can grow with or without oxygen but prefer oxygen for efficient energy production.

_____ Anaerobes: Cannot survive in the presence of oxygen and rely on anaerobic respiration or fermentation.

_____ Anaerobes: Do not use oxygen but can tolerate its presence while relying on fermentation.

_____-aerophiles: Require oxygen at lower concentrations than atmospheric levels for optimal growth.

reactive

oxidizer

oxidizer

most

Oxygen Toxicity;

1. Singlet O2: _____

O2 boosted to higher-energy state

2. Superoxide Radival O2: strong _____

superoxide dismutase

3. Hydrogen Peroxide: _____

catalase, peroxidase

4. Hydroxyl Radical OH-: _____ reactive

catalase

Carbon

Structural backbone of organic molecules

Nitrogen, sulfur, phosphorus

Component of DNA, proteins, and ATP

• nitrogen fixation

• decomposition of proteins

Trace elements

Organic growth factors

_____ _____: Function as cofactors and enzymes

_____ _____ _____: Some vitamins and amino acids

Biofilm

Functional microbial communities

Form slime or hydrogel to attach to a surface

• enclosed in an adhesive matrix

defense

niche

70%

What are some reasons biofilm forms?

1. Self _____

2. Allows cells to remain in a favorable _____

3. Allows cells to live in close association with each other

Involved in what percent of infections?

1000x resistant to microbicides

Growth medium

Sterile

Inoculum

Culture

Microbial Growth in the Lab;

_____ _____: Nutrients prepared for microbial growth

_____: No living microbes

_____: Introduction of microbes to a medium

_____: Microbes that grow & multiply in a culture medium

Agar

100, 40

_____;

Complex polysaccharide

Used as solidifying agent

Liquifies at what? Solidifies at what? (Celsius)

Chemically defined

_____ _____ media: Exact chemical composition is known

Complex

peptones

_____ media: Extracts and digests of yeasts, meat, or plants

Contains partially digested proteins (_____), vitamins, and minerals

Selective

_____ Medium: Suppress unwanted microbes and encourage desired microbes

Contains inhibitors to suppress growth

Differential

_____ Medium: Allows colonies of desired organism to be distinguished from other colonies

Alpha

Beta

Gamma

_____ hemolysis: Partial hemolysis of red blood cells, producing a greenish discoloration around bacterial colonies on blood agar.

_____ hemolysis: Complete hemolysis of red blood cells, creating a clear zone around bacterial colonies on blood agar.

_____ hemolysis: No hemolysis, with bacterial growth but no change in the blood agar surrounding the colonies.

Reducing

_____ Media: Contains chemicals that combine O2

Heated to drive off O2

Enrichment

_____ Culture: Encourages growth of desired microbe

• Increasing very small numbers of desired organism to detectable levels

• Usually liquid

Pure

Colony

Streak plate

_____ culture: contains only one strain or species

_____: Population of cells arising from a single cell or spore or from a group of attached cells (colony forming unit: CFU)

_____ _____ method: isolate pure cultures

Deep freezing

Lyophilization

Preserving cultures;

_____ _____: -50 to -95 C

_____: Frozen. (-54 to -72 C) and dehydrated in a vacuum

Growth curve

_____ _____: Increased number or mass measured in a function of time

4 phases;

Lag phase

Log/exponential phase

Stationary phase

Death phase

Lag

_____ Phase: Growth essentially 0

Enzyme and protein synthesis

Exponential

_____ Phase: Cells divide rapidly and the population doubles with each generation

Stationary

_____ Phase: No net decrease or increase

Death

_____ Phase: Population decreases at exponential rate

Direct

_____ Microscopic Count: Directly counting individual cells under a microscope

Difficult to count small cells

Cannot distinguish living vs dead cells

Viable Plate Count

_____ _____ _____: Used to estimate the number of living bacteria in a sample by counting the colonies that grow on an agar plate after diluting the sample

Serial Dilutions

_____ _____: Used to systematically reduce the concentration of a microbial suspension or solution. This is done by transferring a known volume of the sample into a larger volume of dilutent

Membrane Filtration

_____ _____ Count: A method used to estimate the number of bacteria in a liquid sample

Turbidity

Indirect measurement

Measurement of cloudiness with a spectrophotometer

Psychrotrophs

A soup container was forgotten in the refrigerator and shows contamination. The contaminants are probably which of the following?

Thermophiles

Acidophiles

Mesophiles

Psychrotrophs

Psychrophiles

30-33 C

The bacterium that causes Hansen's disease (leprosy) infects mostly the extremities of the body. What can be its optimum temperature of growth?

Hot vent at pH 1.5

In which environment are you most likely to encounter an acidophile?

Human blood at pH 7.2

A hot vent at pH 1.5

Human intestine at pH 8.5

Milk at pH 6.5

Halotolerant

Bacteria living in salt marshes are most likely which of the following?

Acidophiles

Barophiles

Halotolerant

Thermophiles

Halophiles

Fish sauce is a salty condiment produced by using fermentation. What type of organism is likely responsible for the fermentation of fish sauce?

The organisms are facultative anaerobes

An inoculated thioglycolate medium culture tube shows dense growth at the surface and turbidity throughout the rest of the tube. What is your conclusion?

The organisms die in the presence of oxygen

The organisms are facultative anaerobes.

The organisms should be grown in an anaerobic chamber.

The organisms are obligate aerobes.

The time it takes for a cell to divide or

Generation time can best be defined as…?

The length of time it takes for lag phase

The duration of log phase

The time it takes for a cell to divide

How many generations a cell can divide

1024

Starting with one bacterial cell, how many cells would you have after 10 generations?

10

20

200

1024

Serial dilution

Which process is used to ensure that plates contain 30 to 300 colonies when counted?

Turbidity

Serial dilution

Filtration

Pour plates