Lecture 5- effects of pH and osmolarity on microbial growth Flashcards
at what pH do most microorganisms grow best at?
between pH 6 to 8
what pH do acidophiles grow best at?
low pH (less than 6)
what pH do alkaliphiles grow best at?
high pH (more than 9)
what is the internal pH of acidophiles and alkaliphiles?
internal is still neutral, around 7 (they just grow best at more acidic or basic pH, doesnt mean their internal pH is acidic or basic)
what is the cytoplasmic membrane pH?
the growth pH of the microorganism (ex. acidophile cytoplasm would be less than 6)
how does media handle this pH varience?
it contains buffers, to maintain a constant pH
if bacteria produced acids what would that mean for pH? if bacteria grows on amino acids, what does that mean for pH?
producing acids would decrease pH
growing on amino acids releases ammonia which increases pH
what does water activity mean for microbial growth?
it is the amount of water availability
defined as the ratio of vapor pressure of air in equilibrium with a substance or solution to the vapor pressure of pure water
(water activity represents the amount of water that is interacting with ions and polar compounds in solution)
typically, the cytoplasm has a higher solute concentration then the surrounding environment, what does that mean for the cell?
water moves into the cell creating turgor pressure
when a cell is in an environment with higher external solute concentration, what does that mean for the cell?
water will flow out (cells can have mechanisms preventing this)
what is a halophile? when does it grow best? what does it require
grows best at reduced water potential and has a specific NaCl requirement
what is a extreme helophile? when does it grow best? what does it require?
requires high levels of NaCl for growth (ex. microbes in a salty lake)
what is a halotolerant? when does it grow best? what does it require?
grows best at lower solute concentration
can tolerate some reduction in water activity
what is an osmophile?
organisms that grow with high sugar as solute
what is a xerophile?
organism able to grow in very dry environments
what combination of salt and pH prevents the growth of most pathogens?
high osmolarity
high salt
low pH
use high salt with cabbage to make kimchi because cabbage produces acid (so we dont but any acid in the broth like vinegar)
how do mechanisms combat low water activity in surrounding environment?
increasing internal solute conc by pumping inorganic ions from environment into cell and by producing organic solutes
what are compatible solutes?
compounds used by cell to counteract low water activity in surrounding environment
how can differences in oxygen tolerance be measured?
using thioglycolate broth
what is thioglycolate broth?
complex medium that separates microbes based on oxygen requirements
how does thioglycolate broth work?
reacts with oxygen creating an anaerobic environment
what is the oxic zone and the anoxic zone of test tube using thioglycolate broth?
thioglycolate contains an oxygen responsive dye that turns pink in the presence of oxygen (oxic zone) and colorless when oxygen is low or absent (anoxic zone)
what is an obligate aerobe?
requires oxygen
what is a stric anaerobe?
doesnt require oxygen and may even be killed by exposure
what is a facultative aerobe?
can live with or without oxygen but will use oxygen when its avaliable
what is a microaerophile?
can use oxygen only when it is present at levels reduced from that in the air, it is killed by atmospheric oxygen levels
what is aerotolerant anaerobe?
can tolerate oxygen and grows in its presence even though they cant use it
what does an obligate aerobe look like in the thioglycolate tube?
at the top of the tube in the oxic zone
what does a strict anaerobe look like in the thioglycolate tube?
grows only at the bottom of the tube in the anoxic zone
what does a facultative aerobe look like in the thioglycolate tube?
grows throughout the tube but grows better in the oxic zone
what does a microaerophile look like in the thioglycolate tube?
grows between oxic zone and anoxic zone and forms a narrow band
what does an aerotolerant anaerobe look like in the thioglycolate tube?
grows well throughout the tube
what two techniques are used to grow anaerobic microbes in the lab?
reducing agents may be added to culture media to reduce oxygen (thioglycolate, H2S, sulfur containing compound)
removal of air and replacement with an inert gas like nitrogen or argon
what are 3 forms toxic oxygen that can be formed spontaneously in the cell?
superoxide anion
hydrogen peroxide
hydroxyl radical
what is used to neutralize these toxic oxygen? 4
enzymes:
catalase
peroxide
superoxide
superoxide reductase
do obligate anaerobes have these neutralizing enzymes?
most obligate anaerobes lack some or all of them
