6-2: Culturing microbes

Question 1

Most of a microbial cell weight made of

Answer 1

Proteins, then nucleic acid

Question 2

What are the key elements required to build the core macromolecules used by the cell

Answer 2

C, H, O, N, P, S

Question 3

Where do H and O come from

Answer 3

water

Question 4

What does Mg2+ do

Answer 4

Stabilizes negative charges in membranes, nucleic acids

Question 5

Where do microbes get H/O/P/S

Answer 5

organic molecules

Question 6

What is growth media/culture media

Answer 6

Highly variable depending on the microbe

Question 7

What is defined media

Answer 7

Media prepared by adding precise/known quantities of chemicals to water (exact composition known)

Question 8

What is complex media

Answer 8

Contains extracts or digested organic material with an unknown composition

Question 9

Advantage of defined media? Complex media?

Answer 9

Defined = know what you’re working with
Complex = common, cheaper, easier, broader

Question 10

The inability to produce a molecule you need for growth is… The opposite is…

Answer 10

Auxotrophy = cannot
Phototrophy = can

Question 11

Example of a microbe that can make all/most of the organic molecules they need from a few basics, lives in nutrient-poor environment

Answer 11

E coli

Question 12

Microbes may require a great number of growth factors, like…

Answer 12

Vitamins, a.a., purines/pyrimidines

Question 13

What is selective media

Answer 13

Used to isolate limited assortment of microbes, maybe a single species. Positive selection (nutrients few organisms can use to grow) and negative selection (kill most microbes)

Question 14

What is differential media

Answer 14

Contain some sort of an indicator (e.g. dye) when particular organisms are present

Question 15

What are enrichment cultures

Answer 15

Similar to selective, but less selective and richer. Promotes growth of particular microbes from samples

Question 16

What are solid plates good for?

Answer 16

Solid = isolate single colonies, originate from single cell, easily seen, pure cultures

Question 17

How are all media selective?

Answer 17

99.9% of microbes in a sample don’t grow on plates - most microbes not culturable

Question 18

What is syntropy

Answer 18

Microbes feeding off one another, microbes require other community members to grow

Question 19

Four methods of counting microbial cell numbers

Answer 19

1. Direct count - count cells using microscope
2. Viable plate counts - small sample spread on agar plates then counted
3. Turbidimetric - absorbance of light measured by spectrophotometer
4. Indirect methods - O2 consumption, CO2 production, etc

Question 20

How does direct count work? Disadvantage?

Answer 20

Volume added to gridded microscope slide, cells counted under microscope
No growth required, but very laborious /inaccuracies (viable vs dead)

Question 21

How does viable plate count work? Disadvantage?

Answer 21

serial dilutions
Need to know how to grow specific microbe
Assume colony from single cell
Some cells viable but non-culturable

Question 22

How does turbidity measurement work?

Answer 22

Microbes scatter light proportional to number of microbes in sample
Reliable, but only works in pure cultures and liquid cultures
Not labor intensive, growth continuously measured

Question 23

Major disadvantage of turbidity measurement?

Answer 23

Limited range
Low cell # = insufficient light scattering
High cell # = signal saturated

Question 24

What is microbial growth

Answer 24

Increase in population size via cell division

Question 25

What is generation time

Answer 25

Amount of time it takes for one cell to become two cells.

Question 26

What are batch cultures

Answer 26

Cultures in a fixed volume in a closed container like a flask/test tube

Question 27

What are continuous cultures

Answer 27

Cultures within systems where waste products are being removed and new media fed in

Question 28

What is the lag phase in batch cultures

Answer 28

Period of slow/no growth as microbes adjust to new environment (variable)

Question 29

What is the exponential phase of batch cultures

Answer 29

Growing population doubles at regular intervals. Nutrients still available, little waste

Question 30

What is the stationary phase of batch cultures

Answer 30

Nutrients begin to be limiting, waste accumulation inhibits growth
Little to no net growth (but bacteria still growing and dying)

Question 31

What is the decline phase of batch cultures

Answer 31

Cells start to die, net decline

Question 32

What does generation time depend on? What is the equation

Answer 32

Depends on microbe/growth conditions

Generation time = (growth time) / (number of generations)

Question 33

Exponential phase growth equation

Answer 33

Nt = N0 x 2^n
n=number of generations

Question 34

Is long term exponential growth feasible?

Answer 34

No, would lead to large numbers of microbes accumulating in short time

Question 35

Planktonic vs sessile growth

Answer 35

Planktonic = free living organism in liquid
Sessile = growth attached to surface (common in real world)

Question 36

Sessile growth can develop into

Answer 36

Biofilms - cells encased in polysaccharide matrix

Question 37

Biofilm formation process

Answer 37

Planktonic cells attach to surface via pili, fimbriae, flagellum
Colonization begins (cells multiply) and produce extracellular polysaccharides
Cells change biological program to facilitate biofilm lifestyle
Some cells begin to disperse, resume planktonic lifestyle