Environmental Effects on Microbial Growth

Question 1

higher temperature effects on growth and survival

Answer 1

-increasing rates of enzymatic reactions, but at a point, proteins start to denature, the membrane loses integrity etc

Question 2

lower temperature effect on growth and survival

Answer 2

-reactions proceed very slowly, membrane fluidity becomes an issue and transport is ineffieicent

Question 3

psychrophile

Answer 3

-optimal growth rate below 15 C

Question 4

mesophile

Answer 4

most of the commonly studied widespread organisms
-grow at intermediate temperatures
-ecoli and salmonella

Question 5

-themophil

Answer 5

-optimal growth greater than 45C

Question 6

hyperthermophile

Answer 6

-optimal growth rate greater than 80C

Question 7

psychrophiles

Answer 7

-grow optimally at low temperatures

Question 8

psychotolerant

Answer 8

-organisms can grow at low temperatures but grow optimally as mesophiles

Question 9

when are many psychophiles killed

Answer 9

-room temperature kills them

Question 10

adaptations of psychrophilrd

Answer 10

-proteins have different elements to permit proper folding at low temps -fewer rigid structural elements to remain flexible
-cell membrane phospholipids have increased SCFA and unsaturated fatty acids to allow it to remain fluid
-cold shock proteins to help protein/RNA folding at low tempeprtatures
-cryptoprotectants such as anti-freeze proteins to prevent ice formation

Question 11

does cold always kill other organisms

Answer 11

-no, just prevent growth
-bacteria are commonly stored at -80C in 10% glycerol or 10% DMSo solution

Question 12

what domain of life grows at temperatures above 60C

Answer 12

-prokaryotes
-certain bacteria can grow up to 95C
-certain archaea can grow up to 122C

Question 13

thermophiles and hyperthermophiles adaptations to high temperatures

Answer 13

-protein strcuture adjustments, increased numbers and strength of intramolecular interactions
-heat stabalizing solutes are produced to high levels to help support protein structure
-fatty acids are longer and more saturated (archaea using lipid monolayer helps at higher temp)
-heat stable enzymes from these organism have signifcant commercial utility (PCR needs heat stable DNA polymerase)

Question 14

acidophiles

Answer 14

-acidophiles thrive in acidic environments
-acid-tolerance prefer nuetral pH

Question 15

alkaliphiles

Answer 15

-prefer a pH>8
-some grow at pH up to 12

Question 16

cytoplasmic pH of acidphiles and alkaliphiles

Answer 16

-varies in these organisms but is generally maintained by a range of strategies

Question 17

stomach pH

Answer 17

-important barrier that protects from infection
-acid tolerance of enteric pathogens has infleunce on infective dose
-V cholera < salmonella< shigella
-buffering (increasing) pH of stomach can lead to lower infectious dose

Question 18

osmolarity and microbial growth/suribval

Answer 18

-higher concentrations of solutes in environment leads to water leaving the cell causing shrinking and dehydration
-low concentration of solutes in the enviornmnet - water flows into cell - cell can burst
-salt concentration most signifcant osmotic factor in nature

Question 19

halophiles

Answer 19

-live in high salt environmnets
-extreme halophiles typically require high salt concentrations in order to survive

Question 20

compatible solutes

Answer 20

-key strategy for high solute environments: increase cytoplasmis solute concentration and prevent dehydration
-compatible solutes are solutes produced for this purpose. must be able to accumulate to high levels without interfering with cells biochemical processes
-highly water soluble and inert
-KCl common for extreme halophiloc archea
-AA common for nonphototropic bacteria

Question 21

obligate aerobes

Answer 21

-oxygen required
-aerobic respiration

Question 22

facultative aerobes

Answer 22

-oxygen not required but growth better with O2
-aerobic respiration, anaerobic respiration and fermentation

Question 23

microaerophilic aerobes

Answer 23

-oxygen required but at levels lower than atmospheric
-aerobic respiration

Question 24

aertolerant anaerobes

Answer 24

-oxygen not required and growth no better with O2 present
-fermentation

Question 25

obligate anaerobes

Answer 25

-Oxygen lethal
-fermentation

Question 26

anoxic environments

Answer 26

-in these environments O2 respiration provides no advantage
-O2 not reactive or toxic but presence of O2 reactive oxygen species are geenrtated through reduction of O2
-aerobic/ aerotolerant organisms produce enzymes to detoxify these molecules

Question 27

adaptation recurring themes

Answer 27

-archaea especially have been able to adapt and thrive in any extreme environment
-adapting to extremes generally means being poorly adaptied to more moderate conditions
-tolerance is not the same thing as thriving