Lecture 5- effects of pH and osmolarity on microbial growth

Question 1

at what pH do most microorganisms grow best at?

Answer 1

between pH 6 to 8

Question 2

what pH do acidophiles grow best at?

Answer 2

low pH (less than 6)

Question 3

what pH do alkaliphiles grow best at?

Answer 3

high pH (more than 9)

Question 4

what is the internal pH of acidophiles and alkaliphiles?

Answer 4

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)

Question 5

what is the cytoplasmic membrane pH?

Answer 5

the growth pH of the microorganism (ex. acidophile cytoplasm would be less than 6)

Question 6

how does media handle this pH varience?

Answer 6

it contains buffers, to maintain a constant pH

Question 7

if bacteria produced acids what would that mean for pH? if bacteria grows on amino acids, what does that mean for pH?

Answer 7

producing acids would decrease pH
growing on amino acids releases ammonia which increases pH

Question 8

what does water activity mean for microbial growth?

Answer 8

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)

Question 9

typically, the cytoplasm has a higher solute concentration then the surrounding environment, what does that mean for the cell?

Answer 9

water moves into the cell creating turgor pressure

Question 10

when a cell is in an environment with higher external solute concentration, what does that mean for the cell?

Answer 10

water will flow out (cells can have mechanisms preventing this)

Question 11

what is a halophile? when does it grow best? what does it require

Answer 11

grows best at reduced water potential and has a specific NaCl requirement

Question 12

what is a extreme helophile? when does it grow best? what does it require?

Answer 12

requires high levels of NaCl for growth (ex. microbes in a salty lake)

Question 13

what is a halotolerant? when does it grow best? what does it require?

Answer 13

grows best at lower solute concentration
can tolerate some reduction in water activity

Question 14

what is an osmophile?

Answer 14

organisms that grow with high sugar as solute

Question 15

what is a xerophile?

Answer 15

organism able to grow in very dry environments

Question 16

what combination of salt and pH prevents the growth of most pathogens?

Answer 16

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)

Question 17

how do mechanisms combat low water activity in surrounding environment?

Answer 17

increasing internal solute conc by pumping inorganic ions from environment into cell and by producing organic solutes

Question 18

what are compatible solutes?

Answer 18

compounds used by cell to counteract low water activity in surrounding environment

Question 19

how can differences in oxygen tolerance be measured?

Answer 19

using thioglycolate broth

Question 20

what is thioglycolate broth?

Answer 20

complex medium that separates microbes based on oxygen requirements

Question 21

how does thioglycolate broth work?

Answer 21

reacts with oxygen creating an anaerobic environment

Question 22

what is the oxic zone and the anoxic zone of test tube using thioglycolate broth?

Answer 22

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)

Question 23

what is an obligate aerobe?

Answer 23

requires oxygen

Question 24

what is a stric anaerobe?

Answer 24

doesnt require oxygen and may even be killed by exposure

Question 25

what is a facultative aerobe?

Answer 25

can live with or without oxygen but will use oxygen when its avaliable

Question 26

what is a microaerophile?

Answer 26

can use oxygen only when it is present at levels reduced from that in the air, it is killed by atmospheric oxygen levels

Question 27

what is aerotolerant anaerobe?

Answer 27

can tolerate oxygen and grows in its presence even though they cant use it

Question 28

what does an obligate aerobe look like in the thioglycolate tube?

Answer 28

at the top of the tube in the oxic zone

Question 29

what does a strict anaerobe look like in the thioglycolate tube?

Answer 29

grows only at the bottom of the tube in the anoxic zone

Question 30

what does a facultative aerobe look like in the thioglycolate tube?

Answer 30

grows throughout the tube but grows better in the oxic zone

Question 31

what does a microaerophile look like in the thioglycolate tube?

Answer 31

grows between oxic zone and anoxic zone and forms a narrow band

Question 32

what does an aerotolerant anaerobe look like in the thioglycolate tube?

Answer 32

grows well throughout the tube

Question 33

what two techniques are used to grow anaerobic microbes in the lab?

Answer 33

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

Question 34

what are 3 forms toxic oxygen that can be formed spontaneously in the cell?

Answer 34

superoxide anion
hydrogen peroxide
hydroxyl radical

Question 35

what is used to neutralize these toxic oxygen? 4

Answer 35

enzymes:
catalase
peroxide
superoxide
superoxide reductase

Question 36

do obligate anaerobes have these neutralizing enzymes?

Answer 36

most obligate anaerobes lack some or all of them