Lecture 2 Bacterial growth and its measurement Flashcards
What are the method of measuring growth and what are their limitations?
1.Direct Microscopic Count:
inaccurate, does not tell us if they’re alive or dead, bacteria may be motile
2.Viable count or colony count:
does not occur instantly
3.Turbidity or Optical density; indirect measurement of bacterial numbers. Very fast
limitations: does not distinguish between live and dead cells, or what kinds of cells they are, might contain contaminate, solutions is not homogenous
What are heterotrophs?
like__; they require an organic carbon source
such as: ____, ____, _____
Autotrophs
Can get all of the carbon source they need to build cell structures from CO2 in the air by performing ______.
Nitrogen-fixing bacteria
Can convert atmospherirc N2 (gas) to NH4+ (ammonium) and assimilate it into cellular structures.
_____ MUST use O2 as a electron ____ in respiration (like us).
Obligate aerobes, acceptor
______ live ONLY in places where the O2 concentration is _____(not high and not zero)
Microaerophiles, low
_____ neither use ____ for respiration nor are harmed by it. They ignore it and do’t grow any faster or slower if O2 is present.
Aerotolerant anaerobes, O2
_____ can either use O2 on respiration or use other metabolic strategies when no O2 is available, but will grow ____ when O2 is present.
Facultative anaerobes, faster
____ Must avoid O2, or key enzymes will be harmed and they will die, such as _____
Obligate anaerobes, archaea
exponential growth equation N = N0 * 2^n
N= ___
N0= ____
n = ____
doubling time or generation time g = t/n
initial cell number, final cell number, n= number of generations
t= time
_______ are Conditions in the batch culture or local environment change so that microbial growth is limited,
cells _____
cells _____
There’s no net increase or increase in cell number
________ and some _______ can continue
Stationary phase, runs out of an essential nutrient, accumulate a toxic waste product, energy metabolism and biosynthetic process.
______ phase
Occurs when a stationary-phase culture is diluted into fresh medium
When cells are transferred from rich to minimal medium
When a culture is transferred to different conditions of temperature or stress
lag phase
Temperature
What problem arises?
What adaptation helped them thrive in the extreme?
What adaptations must be evolved and which can be turned on and off as they encounter different conditions?
Heat :
Problem : Cause protein denaturation; collapse of the cytoplasmic membrane; thermal lysis; membranes are too fluid, can’t maintain barrier against the environment
Solutions:
Individual proteins are more stable because they contain fewer glycine residues or have increased ionic bonding between basic/acidic amino acids and their hydrophobic cores
Cells synthesize chaperones that refold denatured proteins
Cells synthesize solutes that help stabilize proteins
Cells produce phospholipids with longer, saturated fatty acids
Temperature
What problem arises?
What adaptation helped them thrive in the extreme?
What adaptations must be evolved and which can be turned on and off as they encounter different conditions?
Cold :
Problem : Thermal motion, reactions very slow; membrane fluidity decrease which inhibits the function of critical proteins in the membrane; ice crystal form in cytoplasm and puncture cell wall
Solutions:
Individual proteins are more flexible than their counterparts in mesophilic or thermophilic bacteria
Cells produce phospholipids with shorter, unsaturated fatty acids; higher content of glycine
Cells produce cryoprotectants (glycerol, sugars) at high concentrations that prevent ice crystal formation
Osmolarity
What problem arises?
What adaptation helped them thrive in the extreme?
What adaptations must be evolved and which can be turned on and off as they encounter different conditions?
Problem:
hypotonic medium, in order to equalize the pressure, between the outside and inside, water usually flows into the cell wall which dilutes the cytoplasm and causes cell lysis.
loss of water beyond a critical point stops enzyme function and growth
Solutions:
Bacteria have rigid cell walls that can withstand internal pressure and prevent osmotic lysis.
They have mechanosensitive channels that are activated by high internal pressures, which leak specific solutes out of the ell to reduce internal osmolarity.
Increase the solute concentration inside, which are small molecules or ions that do not disrupt cell metabolism, helping cell to retain water
ex: sugars, amino acids, glycerol, K+
