G: Environmental Factors Influencing Growth Flashcards
What does -phile mean
means prefer and often means requires
What does -tolerant mean
will grow in a wider range of conditions than non-tolerant
What does -facultative mean
optional mode
What does -obligate mean
an absolute requirement
What does -hyper mean
above/greater than
What does -extreme mean
outside of normal range
How is water activity expressed as, and what does it reflect
aw, reflects how wet/dry an environment is and concentration of solutes dissolve in the water
Equation for aw
aw= Psoln/Pwater where =vapour pressure
Give the range of aw. What does this mean
0 to 1. The higher the [soulte] the lower the water activity. Water has an aw of 1
How does bacterial cells in an environment with high aw protect themselves
by their peptidoglycan
When will bacterial cells undergo plasmolysis
in an environment with low aw (<0.9)
What is the typical aw minimum for bacteria
0.95-0.98
What are osmotolerant bacteria called if solute is NaCl
halotolerant
give an example of halotolerant bacteria and aw limit
Staphyloccocus spp. lower limit is 0.85
What are halophiles
adapted to grow in presence of salts like NaCl, require high levels to grow
How do osmotolerant and halophilic bacteria prevent plasmolysis
must keep internal [solute] the same or higher than that of enivironment
How is internal [solute] the same as the enivironment. Hint: uptake
by uptake of synthesis of a compatible solute
What are compatible solutes
hydrophilic molecules/ions that do not affect cellular fn. eg aa, sugars or ionic compounds like KCl
Would H+ work as a compatible solute
no too acidic, must select stg that is neutral to environment
application of water availability
food preservation: dried or freeze dried (water is frozen and then sublime in a vacuum) and sugar/salt added
How can bacteria be preserved
lyophilized (freeze dried)
what is the optimal pH
it varies, bacterial growth is affected by environmental pH
acidophiles optimum pH is
under 5.5
most bacteria have a pH of? they are called
optimal pH of 7 called neutrophiles
give an example of neutrophile
gram -ive Helicobacter pylori
how does Helicobacter pylori protect itself from stomach acid
secretes urease. substrate for urease is urea. one product of this rxn is ammonia which can bind hydrogen ions and therefore increase the pH
alkalophiles optimum pH is
over 8.0
application of alkalophiles
some Bacillus spp. can secrete proteases and lipases that are stable at high pH. theses enzymes are produced industrially and added to laundry detergents
what does the optimal pH refer to
extreme environment only. cytoplasmic pH must remain near neutral (in most bacteria) to prevent denaturation of proteins and nucleic acids
Why are buffers added to batch culture media
some bacteria produce waste products that change pH of environment. buffers keep media at optimal pH for the species being grown
name an acid tolerance bacteria
E. coli O157:H7 has adapted to lower pH, helps it survive acidic human stomach
