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Microbiology 200 > Topic 4-L2 - Culturing Microbes > Flashcards

Topic 4-L2 - Culturing Microbes Flashcards

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Biology 101 flashcards
1
Q

Half of that weight of a microbial cell is

A

protein, ~ 25% is nucleic acid (mostly

ribosomes!), much of the rest is the cell envelope

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2
Q

Microbes also require lower

A

abundance molecules (e.g. enzymatic cofactors)

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3
Q

Although a lower % of cell material,
availability of these low-abundance
nutrients can dictate

A

growth of a microbe

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4
Q

CHONPS

A

Key elements to build core macromolecules by cells (protein, DNA)

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5
Q

Mg2+ plays key roles in stabilizing

A

negative charges in membranes, nucleic acids – also used by enzymes

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6
Q

Many organic “micronutrients” & trace metals are required a very low
amounts

Microbes that require these (often scarce) nutrients often evolve highly

A

efficient mechanisms for their uptake

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7
Q

Essential cations and anions for cells

A

Na, Mg,K,Ca,Cl

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8
Q

Growth media or culture media (medium, singular) can be highly variable depending on the

A

microbe…and for a given microbe

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9
Q

Defined media:

A

Media prepared by adding precise/known quantities of chemicals to water. Know the exact composition.

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10
Q

Complex media:

A

Contain extracts or digested organic material with an unknown composition. E.g. yeast extract, casein (milk protein) digests

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11
Q

Defined medium has the advantage that

A

you know what you’re

working with.

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12
Q

Complex media advantage is that they are very

A

common – cheaper, easier, work for a broad(er) array of different microbes

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13
Q

Other microbes can require a great number of growth factors – things like vitamins, amino acids, purines/pyrimidines, etc.

A
  • Many organisms have an obligate symbiotic lifestyle
  • Organisms that live in nutrient-rich environments (such as many lactic
    acid bacteria)
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14
Q

Some microbes can make most or all of the organic molecules they need

A
  • Many microbes that live in nutrient-poor environments

- Certain “flexible” microbes that adapt to many different environments
such as E. coli

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15
Q

Auxotrophy –

A

inability to produce a molecule you need for your growth. (Prototrohpy is opposite - can produce that molecule)

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16
Q

E.coli can grow in a complex media contains

A

Peptone and yeast extract

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17
Q

Selective media:

A

Used to isolate a limited range of microbes (often bacteria) – this could be a single species. Often a combination of positive (nutrients few organisms can grow on) and negative (substances that kill most microbes) selection.

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18
Q

Differential media:

A

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

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19
Q

Enrichment culture:

A

Similar idea to selective media…but less selective and richer medium. Promotes growth – increase numbers from isolates to make it easier to isolate a particular microbe. Usually somewhat selective.

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20
Q

Solid plates useful for

A

isolating single colonies –(ideally) originates from a single cell that grows to large numbers & can be readily seen

  • identify morphology, contamination, start pure cultures
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21
Q

Liquid cultures (e.g. used in experiments) should generally be started using

A

isolated single cultures

streaked on agar plates

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22
Q

All media is selective?

A

Yes

23
Q

The great plate count anomaly

A

When “natural” samples are plated on generic growth plates (meant to be “non-selective”)…99.9% of microbes don’t grow.

24
Q

We cannot culture the vast majority of microbes? Why or why not

A

NO we cant, cuz of syntrophy

25
Q

syntrophy

A

(microbes feeding off one

another – microbes require other community members to grow)

26
Q

Counting microbial cell numbers:

A
  1. Direct count: counted using a microscope
  2. Viable plate counts: colonies counted
  3. Turbidimetric: Absorbance of light by a microbe growing in a uliquid culture is measured in a spectrophotometer
  4. Other indirect methods: O2 consumption, CO2 production,metabolic activity. Quantitative PCR to determine the number of
    “genome equivalents”.
27
Q

Direct – microscopic counts

A

Known volume, gridded microscope.

  • doesn’t require growth (advantage)
  • prone to inaccuracies, requires staining. Can confuse microbe with debris.
28
Q

Viable plate counts

A
  • reliable and common
  • need to known how to grow microbe
  • assumes colonies emerge from single cell. (Problem when clumping/aggregating)
  • assume ALL cells grow to form colonies (some cells are viable but aren’t culturable)
29
Q

Turbidity measurements

A
  • microbes scatter light, amount of light scattered proportional to liquid sample. (Common and reliable)
  • correlation b/w optical density and cell #
  • only for single isolated pure cultures in liquid sample
30
Q

A significant advantage of turbidity measurements is that they are not

A

labor intensive and growth can be continuously or regularly measured over time

31
Q

Disadvantage for turbidity measurements

  • Limited useful range:
A

At low low cell numbers, insufficient light scattering not detected. High enough cell numbers saturate signal (no longer linear)

32
Q

Microbial “growth”

A

refers to increase in population size – cell division resulting in multiplying in numbers

33
Q

Generation time (doubling time):

A

The amount of time it takes how long it takes for one cell to become two (cells to double in numbers & mass). Varies greatly depending on microbe & growth conditions

34
Q

Batch cultures -

A

cultures in a fixed volume in a closed container like a flask or a test tube.

35
Q

Continuous cultures –

A

cultures within systems where waste product are being removed and new media fed in

36
Q

Growth phases of batch culture

A
  • Lag phase : adjustment phase
  • exponential phase
  • stationary phase: food limited, waste accum.
  • decline phase
37
Q

Cell numbers double at some regular interval – this interval can vary greatly depending on

A

microbe/growth conditions

38
Q

Generation time formula

A

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

  • g = t/n
39
Q

Growth during exponential phase

A

Total number of cells at any time (N t) will be equal to the starting number of cells (N0) multiplied by 2n, where n is the number of generations

  • Nt = N0 x 2n
40
Q

Exponential growth can lead to very large numbers of microbes accumulating in a short time

In the real world, cells

A

rarely grow exponentially at such as fast rate…but it can happen.

41
Q

Continuous culture

A

Cell can be grown indefinitely in the lab if we can remove waste products (and cells) and add fresh media

42
Q

Chemostat (continuous culture device) can be used to

A

grow cells at a steady state – culture volume, number of cells, nutrient-waste status all kept constant.

  • Cells grow at same rate that they are removed
  • useful for industrial/experimental applications
43
Q

Dilution rate -

A

volume always added & removed at same rate - controls growth rate in cont. culture

  • (To maintain same number of cells…if you replace the full volume every 2 hours, cells must double every 2 hours)
44
Q

Nutrient availability in the medium controls how

A

many cells you’ll have (density of culture)

More nutrients – equilibrium will be established with more cells/ml – greater yield

45
Q

planktonic growth

A

(free-living organisms in liquid)

46
Q

sessile growth

A

(growth attached to a surface)

47
Q

Growth on surface can develop into

biofilms –

A

cells encased in polysaccharide matrix attached to surface

48
Q

In many cases, bio films are complex

A

communities with significant
differentiation (cells with different
properties in different layers of biofilm)

49
Q

Biofilm formation can start with a

A

planktonic cells attaching to a surface

via appendages such as pili, fimbriae or even the flagellum

50
Q

After attachment to surface, the next steps for bio films formation is

A
  • colonization
  • development
  • disperse
51
Q

Colonization begins and the cells

A

grow (multiply) and produce extracellular polysaccharides

52
Q

During development, cells change their biological program - express unique

A

combinations/amounts of genes to facilitate this biofilm lifestyle. Different cells (e.g. surface exposed vs. lower layers), different programs.

53
Q

disperse –

A

resume planktonic state. Form a new biofilm elsewhere?

Microbiology 200 (32 decks)

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