Lab 2

Question 1

What is the equation for Colony forming units (CFU)/ mL

Answer 1

CFU/mL = num. colonies x 1/vol plated x dilution factor

Question 2

What are the positive and negative controls

Answer 2

Positive - undiluted culture (shows does grow)
Negative - Dilutent (shows no growth)

Question 3

What is a standard plate count representative of

Answer 3

The organisms present in the sample that can grow in the medium under the lab conditions

Question 4

Describe Plate count agar (PCA)

Answer 4

Nutritive agar - culture wide range of microorganisms - around 1-10% of soil organisms are culturable

Question 5

What fungi are responsible for the breakdown of plant material

Answer 5

Cellulases and ligninases

Question 6

Describe the mutualistic relationship between fungi and plants

Answer 6

Fungus receives fixed carbohydrate from the plant
Plan receives minerals and water from the fungus

Question 7

Why is Sabouraud dextrose agar preferred when isolating fungi

Answer 7

It has a low pH (5.6) - favourable for fungi and inhibits other fungal species and bacteria
Contains peptones - nitrogenous growth factor
Contains Dextrose - E source

Question 8

Why add penicillin and streptomycin when estimating fungi numbers

Answer 8

These are selective factors - selects against Pseudomonus which survives at 5.6 pH

Question 9

How do you isolate endospores

Answer 9

Heat to sufficient temperature to kill all vegetative organisms but not endospores (~65 degrees for most organisms)

Question 10

What bacteria often form endospores

Answer 10

Gram-positive rods - Bacillus and Clostridium genera’s

Question 11

What is the general composition of an endospore

Answer 11

• Tightly bound walls - high cystine content (binds proteins together)
• Impervious outer wall
• Dry core
  Dipicolinic acid and small acid-soluble proteins in cortex (protects from heat, desiccation, UV and toxic chemicals)

Question 12

What facts can determine the outcome of competition

Answer 12

• rates of nutrient uptake
• Inherent metabolic rates
• Growth rates

Question 13

Describe the competition in our experiment

Answer 13

12 precursor metabolites are required for microbial cells
- E.coli can produce all 12 (through multiple catabolic pathways)
- Streptococcus equi are unable to produce them and rely on the media to provide them

Question 14

What are the three pathways required to produce the precursor metabolites

Answer 14

Glycolysis
Kerbs (TCA) cycle
Pentose phosphate pathways

Question 15

What two broths did we use for our competition experiment and why

Answer 15

Todd Hewitt broth (THB) - provides all metabolites
Minimal Salts broth (MSB) - only provides minimal nutrients needed

Question 16

Describe antagonism

Answer 16

Advantage to one partner and disadvantage to the other. Production of compounds that inhibit the growth of or kill other organisms (some antibiotics are waste products).
- Bacteriocins - ribosomally translated (primary structure directly encoded on DNA)

Question 17

Describe commensalism

Answer 17

Symbiotic relationship - one participant benefits and the other neither benefits nor is harmed
- example - extracellular depolymerase - monomers released provide substrate (organisms around also benefit) - how proteins, polysaccharides and nucleic acids are degraded
- removal of O2 by facultative anaerobe - E. coli in human gut

Question 18

Describe the commensalism relationship in our experiment

Answer 18

Growing antibiotic sensitive organisms in the presence of antibiotic resistant organism (E.coli XL-1) - use ampicillin
- Beta lactamase enzyme produced and exported outside cell to extracellular environment
- Degrades antibiotic containing beta-lactam ring (antibiotic destroyed before interacting with cell)