Microbial Growth

Question 1

what are the essential MACRONUTRIENTS?

Answer 1

carbon, nitrogen, phosphorous, hydrogen, oxygen, sulfur, magnesium ion, iron ion, potassium ion, calcium ion
from: carbohydrates, lipids, nucleic acids, proteins, enzyme cofactors (ions), regulatory molecules (ions)

Question 2

what are the MICRONUTRIENTS?

Answer 2

cobalt, copper, manganese, molybdenum, nickel, zinc ions
mainly from enzyme cofactors

Question 3

what are the chemical reactions of METABOLISM?

Answer 3

CATABOLISM = breakdown of molecules, EXERGONIC, ENERGY OUT
ANABOLISM = build molecules, ENDERGONIC, ENERGY IN
catabolism provides energy for anabolism

Question 4

what percentage of carbon and nitrogen transfer to each level of the pyramid?

Answer 4

10%

Question 5

what are AUTOTROPHS?

Answer 5

get carbon from inorganic sources and use sunlight to make energy

Question 6

describe HETEROTROPHS

Answer 6

get carbon and electrons from organic sources

Question 7

what are CHEMOTROPHS?

Answer 7

get energy from chemical compounds and inorganic compounds

Question 8

describe the NITROGEN CYCLE

Answer 8

need N for amino acids and nucleic acids
nitrogen fixers have enzyme NITROGENASE, converts N2 to NH4+
ex. Rhizobium bacterial species

Question 9

describe the microbial GROWTH CYCLE

Answer 9

most divide by BINARY FISSION –> cell increases in size/cell volume and splits into two equal daughter cells
Population DOUBLES after each division
yeast and some bacteria divide by ASYMMETRICAL BUDDING

Question 10

what is GENERATION TIME

Answer 10

time it takes for a population to DOUBLE
in an OPTIMAL ENVIRONMENT, bacteria divides at a constant rate
Nt = N0 x 2^n
some organisms generate and secrete compounds that are TOXIC to themselves, slowing growth

Question 11

what are the fastest and slowest bacterial generation times?

Answer 11

clostridium perfringens: ~10 mins
Mycobacterium leprae: ~14 days (due to cell wall)

Question 12

how do we MEASURE GROWTH of microbes?

Answer 12

PURE CULTURE (<1% of microbes are culturable)
can understand microbes better than we can in complex environments
use OPTIMAL nutrient and environmental conditions

Question 13

why is it important to understand NUTRIENT REQUIREMENTS?

Answer 13

CHARACTERIZATION of microbes
OPTIMIZED USAGE of beneficial microbes (ex. mass producing pharmaceuticals)
INCREASED UNDERSTANDING of PATHOGENIC microbes

Question 14

why can we not CULTURE MORE microbes?

Answer 14

do not know how to grow in lab
depend on OTHER SPECIES in NICHE
evolved to live INSIDE OTHER CELLS
OBLIGATELY SYMBIOTIC - cannot grow without partners

Question 15

what are the main forms of CULTURE MEDIA?

Answer 15

LIQUID/BROTH: cells held in SUSPENSION –> study in pure culture, obtain LARGE NUMBER of cells & extracellular products

SOLID MEDIA/AGAR: cells grow as COLONY FORMING UNITS –> SEPARATE bacteria, ISOLATE pure culture, study DIVERSITY and TRAITS of a sample

Question 16

what is COMPLEX/RICH media

Answer 16

nutrient rich, composition poorly defined, do not know exact concentrations

Question 17

what is MINIMAL DEFINED media

Answer 17

contain only ESSENTIAL nutrients, concentrations known

Question 18

what is ENRICHED media

Answer 18

specific factors that the microbe cannot produce are ADDED (ex. blood proteins, nucleotides, vitamins///0

Question 19

what is SELECTIVE media?

Answer 19

FAVOUR the growth of ONE organism over another (pH, specific nutrients)

Question 20

what is DIFFERENTIAL media?

Answer 20

exploits BIOCHEMICAL/PHYSIOLOGICAL differences between TWO SPECIES that grow equally well in a medium
ex. miconchi agar changes colour for gram +/-

Question 21

how are pure cultures ISOLATED?

Answer 21

DILUTION STREAKING and SPREAD PLATING

used to establish PURE CULTURES or estimate NUMBER of bacteria
assume ONE CELL = ONE COLONY

Question 22

describe DILUTION STREAKING

Answer 22

work ASEPTICALLY
STERILIZED LOOP picks up small amount of sample
DRAG loop across surface of agar plate
FLAME loop
TOUCH END to LAST streak, repeat streaking

millions of cell divisions produce visible colonies

Question 23

describe SPREAD PLATES

Answer 23

set up 10 fold serial dilution
plate 0.1mL (100 microlitres)
analyze plates with ~30-300 CFUs

Question 24

how is bacteria COUNTED

Answer 24

must be SUSPENDED in liquid
1. direct microscopic counts via HAEMOCYTOMETRY
2. PLATE counts
3. OPTICAL DENSITY using spectrophotometer

Question 25

what is OPTICAL DENSITY?

Answer 25

higher cell concentration = higher TURBIDITY (cloudiness of liquid)
measured as LIGHT SCATTERED by suspension
higher reading = denser cell culture
amount of diffraction is a function of density (NOT a cell count)

Question 26

what is the microbial GROWTH CYCLE?

Answer 26

measure of cell DENSITY/COUNTS over TIME

Question 27

what is the LAG PHASE?

Answer 27

bacteria ADAPTS to new growth conditions
bacteria MATURES and cannot divide
SYNTHESIS of RNA and ENZYMES

Question 28

what is the EXPONENTIAL/LOGARITHMIC phase?

Answer 28

EARLY: cells grow at MAX rate
LATE: SLOWING of growth due to density, competition, waste accumulation

Question 29

what is the STATIONARY PHASE?

Answer 29

population PLATEAUS due to GROWTH LIMITING FACTORS
cells are still ALIVE and METABOLICALLY ACTIVE

Question 30

what is the DEATH phase?

Answer 30

cells DIE due to NUTRIENT DEPLETION and the production of TOXIC BYPRODUCTS

Question 31

what is CHEMOSTAT?

Answer 31

ensures CONTINUOUS logarithmic growth by ADDING and REMOVING equal amounts of CULTURE medium
growth conditions are HIGHLY CONTROLLED
allows study of NATURAL CONDITIONS