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LSCI 230 Study Guide - Midterm Guide: Growth Factor, Microorganism, Escherichia Coli


Department
Life Sciences
Course Code
LSCI 230
Professor
Mira Ovechestcky
Study Guide
Midterm

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Lecture 8: Microbial Growth
Key Questions:
1. How microbes are able to grow and divide.
2. How we are able to quantify the growth of microbes.
3. What environmental factors affect microbes.
Essential Elements
1. Metabolism of most nutrients (N, S
and P) is relatively simple; slight
modification are needed before
incorporation into cellular material.
2. In contrast, sources of carbon and
energy usually undergo many
transformations.
3. Pic shows the essential elements that
microbes need to grow, live, and divide.
A) 50% of E.Coli cells is carbon
B) 17% is O
C) 13% is N
D) 8.2% is H
E) Small amounts of P, S, & Se!!!
4. All these essential elements for microbes comes from the environment in the form of nutrients
5. We got macronutrients that are required in very large amounts and micronutrients that are required in
tiny amounts (still important!). (below)
Sources of Essential Elements: Nutrients
1. Growth factors: GFs pertains to Vitamins, amino acids, purines, pyrimidines or other organic molecules
that the microorganism needs for growth but cannot synthesize by itself.
A) Note that this does not mean that microbes cannot make their own vitamins and aa. There is certain
microbes that can make certain kinds of aa. However, for the aa that they can NOT make, those are called
“growth factors” needs to be provided.
B) Some growth factors are the by‐product or waste of another microorganism.
2. Now, let’s look at macronutrients in details:
Macronutrients are required in large amounts.
A) Carbon can be obtained from organic compounds or CO2. The CO2 can be used as a carbon source from
the atmosphere only if the microbe can fix its own CO2.
B) Nitrogen can be obtained from ammonia (NH3), nitrate (NO3-), nitrogen gas (N2), or organic nitrogen
compounds ( such as amino acids)
C) Hydrogen can be obtained from water or organic compounds
D) Oxygen can be obtained from water, O2 in the air, or from organic compounds
RM

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note that for organic compounds, microbes get their O, H, and C.
E) Phosphorus can be obtained from phosphate (PO43-)
F) Sulfur can be obtained from hydrogen sulfide (H2S), sulfate ( SO42-), or organic Sulfur compounds (e.g.,
Cysteine), and sulfur can also be taken up via the form of metal sulfide (such as FeS, CuS, ZnS, etc.)
G) Potassium is found in solution as a cation (K+ in solution) or it can be taken up as a salt (e.g., KCl).
*Magnesium, Calcium, and Sodium all have the same story. They can all be taken up as ions from solutions
or as salts!
H) Magnesium: Mg2+ in solution or various Mg salts
I) Calcium: Ca2+ in solution or various Ca2+ salts
J) Sodium: Na+ in solution or various Na+ salts
2. Micronutrients are required in trace amounts.
A) Iron: Fe2+, Fe3+
B) Trace metals
**examples of micronutrients shown below in the table
Examples of Micronutrients
1. Micronutrients are
mostly metals.
2. Micronutrients as
trace elements are
often required as co-
factors for enzymes.
A) E.g., Iron is a key
micronutrient.
such as for the
FeS clusters in the
ETC.
B) Thus, if bacteria
has no access to iron,
it can NOT run the
ETC.
3. In many marine
systems, iron tends
to be the limiting
reagent (very true
for cyanobacteria in
the oceans).

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Growth of microorganisms
1. Growth of the population pertains to increase in the
number of cells or biomass.
2. Most prokaryotes multiply by binary fission; the cell
grows in size until it forms a partition (aka a septum) that
constricts the cells into 2 daughter cells.
A) So, we start off with 1 mother cell, and end up with 2
daughter cells.
3. Each daughter cell receives one copy of the
chromosome, sufficient ribosomes, macromolecules,
monomers and other molecules to exist as an independent
cell.
4. The Generation time for E.coli = happens in 20 min in the lab (for the E. Coli mother cell to grow from 1
cell to 2 cells).
Cell division and peptidoglycan synthesis
1. Cell division requires the synthesis of
new cell wall material, and also
requires the destruction of the
peptidoglycan via autolysins.
A) So, as the cell starts to elongate, it
needs to first break its peptidoglycan.
B) The breaking is required to put in
new peptidoglycan subunits and allow
the cell to keep elongating (for cell
division).
C) As shown in the Pic, the cytoplasmic membrane is in the middle, and the peptidoglycan is on top where
we see it breaking.
D) This break occurs thx to Autolysins (an enzyme, similar to lysozyme).
E) There is another enzyme called “Bactoprenol” (below>
2. The Bactoprenol brings in new peptidoglycan subunit to be exported across the cytoplasmic membrane
(in the middle towards being integrated into the new peptidoglycan layer).
A) The process at which new peptidoglycan subunits are integrated is called transglycosylases AND
transpeptidases.
3. When the cell is dividing, we have something called a FtsZ ring in the septum.
A) Called FtsZ ring because its protein monomers are called Ftsz proteins.
B) This ring contracts and allows the two cell to pinch of into two new cells.
4. At the division ring (FtsZ ring), autolysins create some gaps in the peptidoglycan. This allows
rearrangement of the peptidoglycan and synthesis of a new cell wall.
A) Cell division leaves behind scars that we can see via an electronmicroscope.
B) In the pic below, we can see the septum in the middle and the wall band around it.
C) The scar was formed when the autolysins broke the old peptidoglycan.
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