MICRB 265 (10/18/13) Microbial Nutrition and Growth (con't)

4 Pages

Microbiology (Biological Sciences)
Course Code
Brian Lanoil

This preview shows page 1. Sign up to view the full 4 pages of the document.
MICRB 265 (October 18, 2013) Microbial Nutrition and Growth (con’t) Stationary Phase  This phase follows the exponential phase  Cells are still alive but they are not growing in count  Cells often shrink since there is a reduced need for ribosomes  Sporulation becomes more typical in older g+ve cultures when they approach this phase o This is where we start seeing sporulation Reasons for Stationary Phase  Substrate is limited in minimal and defined media  Oxygen is limited in complex media (high respiration and low solubility of oxygen) o 100000x less soluble in liquid than in air o Stationary phase is not due to cell crowding  Diffusion of oxygen is not limited in a colony  Presence of toxins Cryptic Growth  Growth rate = death rate  You can’t tell that the culture is still growing since the numbers don’t change o Bacteria are waiting for conditions to become favourable again  Higher resistance to antibiotics is seen  Antibiotics mainly target growth… since the cell is no longer growing, it is less affected by antibiotics Death Phase  Clear decline in cell number o Rate cannot be predicted or calculated  Rate may be linear or exponential but one thing is for sure… the death phase is NOT a mirror image of the exponential phase!! Decreasing cell count is reliant on different mechanisms as compared to those of exponential growth  Viable, non-culturable phenomenon o Under the microscope, you can see the living cells, however the # of viable colonies you get when you transfer them to an agar plate is lower… o What does this tell you?  Not all cells are metabolically uniform when it comes to differing cultures  Limitations in substrate and nutrients may cause come cells to become cannibalistic in nature… eat other cells in order to survive a bit longer o Some cells actually commit suicide (lyse themselves) to provide nutrients to fellow cells…  When faced with starvation or growth arrest, cell may: o Go through a death phase and there will still be a few survivors o Go through genetically programmed death to provide survivors with nutrients to survive until favourable conditions arrive (hopefully) o Cells may become sterile and will not become active until passing through the digestive system of an animal  Eg. Cholera becomes infection after passing through digestive system of animals Live/Dead Staining  If a cell dies but doesn’t lyse itself, how do you know if it is dead? o Stain them!  Cells are initially stained green.  Then stained with red stain that is able to permeate the damaged membrane of dead cells but not the intact membrane of the live cells.  Red stain pushes out the green dye.  Dead cells appear red and the living cells appear green. o Living definition here = intact cell membrane Measurements of Microbial Growth 1. Direct count a. Cells counted from microscopic slide b. Fastest method and very accurate BUT it takes a plot of preparation i
More Less
Unlock Document

Only page 1 are available for preview. Some parts have been intentionally blurred.

Unlock Document
You're Reading a Preview

Unlock to view full version

Unlock Document

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.