Microbiology Chapter 9 &11

Microbial Growth & Mechanisms of Microbial Genetics

Binary Fission

Dividing/separating in to two (scam because all cells grow)

A method of asexual reproduction in which a single cell divides into two identical cells.

Step 1: Growth

Step 2: Replication

Origin of replication

Same as mitosis attached to intercell membrane

Cytokinesis

CELL DIVISION

FtsZ Protein > Z-Ring > helps as anchor)

Divisome Formation (Dividing Body) (cell wall created where division septum is)

Generation Time (Doubling Time)

Prokaryotes definition =Time for population size to double

doubles to get 2 doubles to get 4

• Examples: Escherichia coli, Staphylococcus aureus, Lactobacillus acidophilus, Rhizobium japonicum, Mycobacterium tuberculosis hard to treat because of doubling , Mycobacterium leprae

Growth Curve

Phases of Growth

Lag Phase

Preparing to divide

Log Phase

Exponential Growth

Stationary Phase

Growth plateau

Rate of cell death is equal to cell growth rate

Death Phase

Exponential decrease in living bacterial cells

Closed Culture

Limited resources and limited space

Petri dish or tube

Inoculum

Initial group of organisms

Virulence Factors

Helps organisms infect and survive in the host

Chemostat System

gets rid of waste and adds new nutrients for continuous culturing of microorganisms

Direct Measurements of Bacterial Growth

COUNTING CELLS

• Direct Microscopic Cell Count

• Coulter Counter

• Viable Plate Count

• Serial Dilution

• Pour Plate SWIRL & Spread Plate SPREAD

• MPN (Most probable Number) - used for drinking water

Indirect Measurements of Bacterial Growth

MEASURES CELL ACTIVITY

• Turbidity via Spectrophotometry- Looking for cloudiness

• Dry Weight- For motile microorganisms

• Measurement of Metabolic Activity- Rate of production/consumption

Formation of Biofilms

Panktonic cells - Attach to hard surface to become sessile cells

EPS Secretion and Cell Division and Water channels formed for nutrient flow

Dispersion of peripheral cells to start a new cycle

Benefits of Biofilm

Prevents access to other molecules that cause harm

Quorum Sensing

Detect if they have enough bacteria

Autoinducers

Produce themselves in gram-negative and gram positive bacteria

Oxygen is reactive (tends to kill stuff)

Oxygen is reactive (tends to kill stuff)

Free Radical Reactive Oxygen Species (ROS)

Extremely reactive

Won’t make it out of their initial location without reacting

• EXAMPLES: Singlet Oxygen(O2),Hydroxyl Radical (OH), Peroxyl Radical(RO2-), Hydroperoxyl (HO2),Alkoxyl Radicals (RO)

Non-Free Radical Reactive Oxygen Species (ROS)

Not quite as reactive

Can escape their original location before reacting

• EXAMPLES: Superoxide(O2-),Peroxides(H2O2),Hypochlorite ion(OCl-)

Obligate Aerobes

Must have oxygen

Obligate Anaerobes

Do NOT want oxygen

Facultative Anaerobes

Aerobes that deal with low oxygen

Aerotolerant Anaerobes

Tolerant in high and low oxygen

Can survive everywhere

Microaerophiles

Need minimal Oxygen

Capnophiles

Less Oxygen more CO2

Detoxification Enzymes

• Superoxide dismutase- breaks down O2-, produces hydrogen peroxide and oxygen(O2)  ,

• Peroxidase- breaks down H2O2, produces H2O

• Catalase- breaks down H2O2, produces H2O and O2 .

  (Obligate anaerobes lack all 3 of these enzymes)

When we have optimal pH for growth

The enzymes is most effective

Effects of pH on cells

Extreme pH affects structure of macromolecules

• DNA strands seperate at low pH

• Lipids hydrolyze at extremely low pH

• Protein structure is disrupted by moderate pH change (PROTEINS ARE THE MOST SENSITIVE TO pH CHANGES)

Proton gradient Affects ATP production

• Reducing the gradient reduces ATP production (due to OH-=H=>H2O)

Acidophiles

like acidity pH below 7

Neutrophiles

Want to be near neutral

Alkaphiles

Above neutral in basic range

Thermal Energy

jiggling of ions at the molecular level

Provides energy for chemical reactions

Excess Thermal energy can disrupt the structure of enzymes and macromolecules

Insufficient thermal energy makes it difficult for enzymes to catalyze reactions

DNA Double Helix Stabilization

Adaptation to Extreme Temperatures

• Increased guanine-cytosine (due to increased hydrogen bonding of G(triplebond)C

Protein Structure Stabilization

Adaptation to Extreme Temperatures

• Additional secondary structures

• Ionic and Covalent bonds

• Replacement of key amino acids to stabalize folding

Osmotic considerations

Natural environments have lower solute concentration than cytoplasm of organisms.

Cell walls protect against osmotically induced rupture

Plasmolysis

shrinking of the cell

I.e. Hypertonic

Hypertonic

Shrinks

Hypotonic

Swells

Halophiles

“SAlt Loving”

Require salt to grow

Halotolerant

Will grow in high salt concentration but don’t require it

Nutritive media

Supports growth of bacteria

All purpose medium- Allows growth of many organisms. Eg Tryptic Soy Broth (TSB)

Enriched Medium - contains growth factors, vitamins,and other nutrients to promote growth of fastidious organisms, which can’t produce some nutrients on their own.

Chemically Defined Media

Like a recipe

Exact chemical composition known

Complex Media

You only approximately know what’s in it

No precise chemical composition

Digests of meat, yeast, or plants

Selective media

Inhibit growth of unwanted organisms, while supporting growth of organism in interest

Enriched Medium

Specific nutrients favoring growth of a specific organism 

Differential Media

How you identify what is growing

Change color of colonies or medium to distinguish the cultures in it

Functions of genetic material

DNA Replication

RNA Transcription

Protein Synthesis

Initiation (DNA Replication)

Origin of Replication- Specific DNA sequence where replication begins

Key Enzymes: Helicase separates DNA strand , Topoisomerase clips strand to prevent supercoiling, Primase primer so you can build on (makes a 5 to 3 prime connection) phosphodiester bond

Elongation (DNA Replication)

(polymerization - nucleotide -nucleotide)

DNA polymerase 3 magic of DNA replication, DNA polymerase 1 replace RNA with DNA at start of each fragment 

Leading 1 primer at the beginning and build continuous strand and Lagging Strands always a little behind cause it can only build in one direction

Okazaki Fragments chunks made in the lagging fragments, new fragments made as DNA opens,

Termination (DNA Replication)

Normal bacteria DNA - Negatively supercoiled, not catenated

Resolution of Supercoils and Catenanes

Role of Gyrase and Topoisomerase IV