Lecture 4: Microbial Growth Flashcards
Growth:
measured as an increase in the number of cells
- in us growth is get bigger –> increase in size of the organism
Binary fission:
cell division following enlargement of a cell to twice its minimum size
1 cell –> 2 cells
- process by which the growth occurs b/c:
1. cells are relatively constant in size
2. organism is unicellular
organism does everything at the same time
- increase in length dividing genetic material, producing ribosomes ( very efficient)
Generation time:
time required for microbial cells to DOUBLE in number
* not all cells have the same generation time its dependent on conditions
During cell division….
(process of binary fission) each daughter cell receives a chromosome and sufficient copies of all other cell constituents to exist as an independent cell
- 2 size identical & genetically identical daughter cells & have all the same comp’s needed for life
Compare growth in Prokaryotes vs eukaryotes
In bacteria and Archaea growth in cell size, chromosome replication and even septum formation typically occur SIMULTANEOUSLY (multitasking)
Contrary to Eukaryotic cells where…growth, replication of DNA and separation via mitosis are separated into interphase and mitosis
- 1st with interphase: duplication of organelles (cell in prep for making 2)
- but then & only then do you progress into S phase - where there is replication of DNA
- then cell will change to make more of what it may not have had (D2 phase), then you go to divide by mitosis (ORDERED)
Does Mitosis occur in bacteria and Archaea
EUK ONLY
How does the generation time of bacterial microbes compare to eukaryotic microbes?
Most bacteria have shorter generation times than eukaryotic microbes
* it takes more than 10 hrs to produce cells for mitosis , mitosis is only 1 hr but the preparation takes longer
\Generation time is dependent on…
growth medium and incubation conditions: carbon source, pH, temperature, etc
- need to be met for organism to thrive, otherwise will be affected
Exponential growth
Growth of a microbial population in which cell numbers DOUBLE at a CONSTANT and SPECIFIC time interval
* cells are doubling each time
A relationship exists between the initial number of cells present in a culture and the number present after a period of exponential growth:
Nt =No x2n
- Nt is the final cell number
- N0 is the initial cell number- before any doubling occurs
- n is the number of generations during the period of exponential growth (# of doubling)
Note: constant interval of time between doublings in this example
What is problematic with exponential growth?
it’s v. challenging to take a time point of 0 & 1 cell, & put it on a graph with a time point of 10 & have 1 million cells
- graph won’t have any meaning b/c on time scale its a small range of #’s, but on the cell # scale, you have 1 & a million & just a few # of data points & in the middle everything is really low compared to 1 million
- so, to create a meaningful, graphical representation of growth isn’t possible, so we show the log plot
Because cells increase exponentially in numbers, the.
increase in cell number is initially slow but increases at an ever faster rate following an exponential curve
• Only when plotting on a log scale can one appreciate that the cells are doubling at a constant rate
Diff. b/t graphical # of cells vs. logarithmic # of cells/reason we DON’T want to graph the # of cells…
b/c they exhibit exponential growth & as a result of exhibiting exponential growth, you see a FLAT section, where a lot is happening but we just can’t see it graphically b/c we’re trying to squeeze such expanded data points on the same y-axis
- b/t 0-100, there’s a lot going on, but its squeezed all together so we all get the jump
what is a way around using an exponential graph?
take log of the # of cells & graph that against time
- becomes clear to us that we have exponential growth (i.e. an increase in cell # over time)
- linear relationship
- can be fit to the equation of a line, y = mx+b –> allow opp. to use the x-value (time), to determine the log # of cells (y-value)
- imp. for counting (makes sense of how many cells will be present with a partic. GM)
When growth is UNLIMITED it is called _____ growth because it generates a curve whose slope ______ ________
UNLIMITED (nothing will get in the way of this growth - b/c as long as they are given nutrients & conditions that they favour; they’ll keep growing, provided that they won’t run out of their necessities)
EXPONENTIAL
INCREASES CONTINUOUSLY (constant b/c of the cells double with each gen. time that passes)
Why is exponential growth a key characteristic?
b/c they can complete binary fission
- b/c organisms can do this doubling (1 cell split in 2) every single time they generate
Growth rate (k)
the rate of increase in POPULATION NUMBER (ex: 10 cells initially, now we have 20 - opp. to increase cell # that can be used to gauge pop. size - # of cells present) or BIOMASS (the ORGANIC material that comprises the cell)
When cell doubles, so does the…
DNA, protein, RNA etc. (AKA the ORGANIC material increase as a conseq of doubling)
Since bacteria and archaea grow by binary fission, the growth rate is expressed as the…
number of DOUBLINGS per hour
- meaning 1 cell splits into 2
- ex: 2 doublings per hour etc., which will characterize that partic. species
Are any organisms that same in terms of growth rate?
NO 2 organisms are the same, b/c growth rate characterize a partic. species & its capabilities
generation time (g)
Growth can also be looked as the time it takes for each cell to become 2 cells, this is called the... # of mins/ gen
The specific growth rate (k) can be calculated using the formula:
k=(LogNt –LogN0) 0.301 Dt
k - determine how many gen’s/hr this organism is characterized by
Where:
• N0 = number of cells at time1
• Nt = number of cells at time2
• Dt = time2 – time1
If there’s 2 doubles per hour = k, what does that mean for the gen. time?
What does that mean about the time it takes for the doubling to occur?
k=2gen/hr
30 mins
What does a k = 1.43 gen/hr mean about the gen time?
k = 1.43 gen/hr
- LESS than a hour - b/c your able to produce more than 1 gen in a 60 min period
generation time formula
(g):
g=1/k
g=1/1.43
= 0.70 hr/gen (less than a hr to complete a gen)
= 42.0 min/gen
For each organism there is a
specific growth rate that is the fastest growth rate in the best growth medium at optimal temperature
Different for each organism
- every organism has their best - working as hard as they can under the best of conditions
- if you take them from their best conditions that support their best growth & move them away from that value, the values will change
(get best k & g value - due to optimal nutrient avail, optimal pH, etc. that will characterize microbial growth)
Clostridium perfringens
can DOUBLE in numbers every 10 minutes under optimal growth conditions (e.g. nice warm stew on a warming plate)
- DANGEROUS for food borne illness b/c it only takes 10 mins to double from for ex 50 cells to 100
- # ’s increasing exponentially in v. short amounts of elapsed time
Escherichia coli
LESS than 30 min in a rich medium
- can do a lot of DAMAGE too
- hamburger disease (v. fast), become sick when eating b/c organism will be so plentiful
- or could spread up urethra to bladder, feeds off N & other things & then enters into blood which is life threatening infection
Mycobacterium tuberculosis
CANNOT grow faster than one doubling every 24 h
- SLOWER than what it takes 1 of our cells to do mitosis
- LONG time
If you take a sputum sample from a person’s who’s potentially infected by TB. You spread it on a petri dish & you come back next day & see?
NOTHING, even if there were 50 or 100 cells that came out of that person’s sputum, b/c it only doubles every 24 hrs, you’re actually leaving that plate in an incubator for weeks - long time to see any indicator of growth
You’re worried that a patient has Mycobacterium TB. Are you gonna take a sputum sample & spread it on a petri dish & put it in an incubator to do a diagnosis?
Yes, BUT it won’t give you a timely diagnosis but you do a acid fast stain and a genetic test to look for resistance
What is the treatment you use for Mycobacterium TB?
antibiotic therapies work for actively growing bacteria
* antibiotic therapy is 6 months long b/c its growing so slowly
