3.5: Other Environment Effects on Microbial Growth

Question 1

some organisms have evolved to grow best at low or high pH, but most grow best between what pH range? what are they called?

Answer 1

• between pH 5.5 and 8
• Neutrophiles

(skewed to acidic side bc lots of natural environments are acidic)

Question 2

what pH do acidophiles grow best at?

Answer 2

grow best at or below pH 5.5

Question 3

what pH do alkaliphiles grow best at

Answer 3

grow best at or above pH 8

Question 4

are acidophiles or alkaliphiles more common?

Answer 4

acidophiles are more common

Question 5

what do acidophiles generally require for stability?

Answer 5

• cytoplasmic membranes require high external H+ concentrations for stability

Question 6

why are alkaliphiles less common than acidophiles?

Answer 6

• fewer naturally basic environments exist

Question 7

what is a problem for alkaliphiles, what’s the solution?

Answer 7

• they have a problem maintaining a H+ gradient when the environment is rich in OH- ions (since when H+ goes out, H+ and OH- combine to make water so it would keep going out and eventually run out)
• Solution: alkaliphiles place more reliance on a sodium motive force (ie. Na+ gradient)

Question 8

what do neutrophiles acidophiles and alkaphiles all have in common?

Answer 8

• Cytoplasmic pH is maintained near neutrality
• this works bc CM has very low permeability H+ and OH- (even in basic conditions, bc OH- ions are hydrophilic and blocked by hydrophobic core of membrane)

Question 9

Microbial culture media typically contain buffers to maintain constant pH, why?

Answer 9

• Each organism has a optimal pH for growth
• some bacteria produce acids (acetic, lactic, sulfuric acid etc…)
• ex. fermentation converts sugars into acid end-products
• some bacteria release ammonia, which increases the pH
• ex. Urease producing bacteria break urea into NH3 and CO2

Question 10

what conditions do Non-halophiles grow best in? what happens with cytoplasm

Answer 10

• Grow best at low salt concentrations < or equal to 1% NaCl
• cytoplasm has higher solute concentration than surroundings
• water has a tendency to flow into cell
• producing turgor pressure
• perfect for growing bacteria

Question 11

what’s halotolerant, and example

Answer 11

• generally grow best at lower solute concentrations, but still tolerate and grow if there’s higher conc.
• ex. staphylococcus aureus
  -lives on human skin
  -grows best at low NaCl
  -but can tolerate up to 17.5% salt

Question 12

what’s the difference between halophiles and halotolerant?

Answer 12

• halotolerant can tolerate high salt conc, halophiles grow better at high salt conc.

Question 13

halophiles

Answer 13

• grow best at high salt conc. reduced water potential; have a specific requirement for NaCl
• many marine microbes

Question 14

extreme halophiles

Answer 14

• require high levels of NaCl for growth (will not grow in regular sea water needs higher salts conc.)
• 15-30%
• ex. Microbes from Great Salt lake

Question 15

cells typically combat high environmental solute concentrations by…

Answer 15

• accumulating compatible solutes in the cytoplasm
• compatible solutes: solutes that don’t interfere with metabolism
• results in net inflow of water

Question 16

what are the 4 most common compatible solutes, which organisms use each one (and what’s the most imporant)

Answer 16

• amino acids: proline, glutamate (most bacteria)
• sugars: sucrose, trehalose (cyanobacteria)
• alcohols: glycerol or mannitol (eukaryotes)
• compatible salts: KCl (extremely halophilic Archaea) (most important)

(in any case they do NOT accumulate sodium)

Question 17

Obligate aerobes

Answer 17

• require oxygen for metabolism (aerobic respiration)

Question 18

strict anaerobes

Answer 18

do not require oxygen and may even be killed by it

(strict that they can’t have oxygen)

Question 19

facultative anaerobes

Answer 19

• can live with or without oxygen, and they will use O2 for respiration when it is available

(ability to switch)

Question 20

aerotolerant anaerobes

Answer 20

can tolerate oxygen and grow in its presence, but they don’t use it for anything (won’t be killed by oxygen/air)

Question 21

Microaerophiles

Answer 21

• Require O2, but can’t tolerate regular atmospheric O2 levels (love only small amount of O2, get killed by large amounts)

Question 22

what is the thiogylcolate broth experiment used for

Answer 22

• demonstrating oxygen response

Question 23

how does the thioglycolate broth experiment for demonstrating oxygen response work

Answer 23

• tube is boiled or put in autoclave so oxygen diffuses up
• thioglycolate reacts with oxygen, so oxygen can’t diffuse deep into tube (stays at top)
• an oxygen indicator turns pink in the presence of oxygen and colourless when the oxygen is low or absent

Question 24

where do obligate, strict, facultative, microaerophiles, and aerotolerant anaerobes grow in the thioglycolate broth experiment

Answer 24

• **obligate aerobes ** -grow only in the oxic zone at the top of the tube (bc they need O2)
• **strict anaerobes ** -grow only in the anoxic zone at the bottom of the tube (bc can’t grow in oxygen)
• ** Facultative aerobes ** -grow throughout the tube
  -but better growth occurs in the oxic zone (use oxygen when they can), where they can generate energy by aerobic respiration.
• Microaerophiles -grow in a narrow band between the oxic and anoxic zones -they need a lil O2 for aerobic respiration
• Aerotolerant anaerobes -grow well throughout the tube
  -don’t use O2 to generate energy
  -but also not harmed by O2

Question 25

what's the difference between aerotolerant anaerobes and facultative aerobes?

Answer 25

* aerotolerant anaerobes aren't affected by presence of oxygen (don't use it) facultative grow better with oxygen

Question 26

what are the special techniques needed to grow strict anaerobes?

Answer 26

* **Reducing agents**: chemicals added to culture media to reduce oxygen (eg. thioglycolate, cysteine, H2S) * Removal of air, and replacement with an inert gas (ex. Nitrogen, used when oxygen needs to be completely removed for the strict anaerobe to grow) -anaerobic jar (only works if strict anaerobe can live while exposed to a little oxygen while being transferred) -anaerobic glove box

Question 27

why does oxygen harm some microbes

Answer 27

* several toxic forms of oxygen can be formed spontaneously in the cell: * Superoxide anion: O2- (extra electron combined with oxygen) * Hydrogen peroxide: H2O2 -stole e- and proton to form: * Hydroxyl radical: OH

Question 28

How do cells protect themselves from toxic forms of oxygen?

Answer 28

* enzymes can be used to neutralize the most toxic oxygen forms * enzymes depend on if they're aerobic anaerobic etc

Question 29

what enzymes do **aerobes and facultative anaerobes** use to protect themselves from toxic forms of oxygen?

Answer 29

* Aerobes and facultative anaerobes normally use the enzymes superoxide dismutase and catalase (carry out aerobic respiration)

Question 30

what are the reactions of superoxide dismutase and catalase enzymes that neutralize toxic oxygen forms? (in aerobes and facultative anaerobes)

Answer 30

* superoxide dismutase (SOD): 2O2- + 2H+ > H2O2 + O2 (Prevents O2 from stealing e- by binding it to another O2, but H2O2 is still not great) * Catalase: (next step that gets rid of H2O2) H2O2 +H2O2 > 2H2O + O2 (these are harmless)

Question 31

How do **aerotolerant anaerobes** protect their cells from toxic forms of oxygen? explain and say reaction

Answer 31

* use superoxide dismutase (SOD) to turn oxygen into hydrogen perioxide, but then use peroxidase to deal with H2O2. * reaction: H2O2 + NADH (provides e- to reduce H2O2) + H+ > 2H2O + NAD+ (no gas produced)

Question 32

**Strict anaerobes** generally lack SOD and catalase, leaving them highly sensitive to oxygen. what do some use to detoxify O2-? state the reaction

Answer 32

* some use superoxide reductase to detoxify O2- * reaction: O2- + 2H+ + rubredoxin (reduced) > H2O2 + rubredoxin (oxidized)

Question 33

**Microaerophiles** normally have low levels of superoxide dismutase (SOD) and catalase, so how else do they protect themselves from toxic forms of oxygen?

Answer 33

* use O2 for respiration on their cytoplasmic membrane before it has a chance to enter the cell (so toxic forms of oxygen don't enter cell)