Environmental influences on microbial growth: pH and osmolarity

Question 1

adaptations to avoid thermal lysis

Answer 1

• more saturated membrane lipids and saturases remodel membranes

* used ffor groth at high temp

-synthesis heat shock proteins and more thermostable proteins (stronger/more bonding)

Question 2

adaptations maintaining a semifluid membrane

Answer 2

• less saturated membrane lipids and desaturases to remodel membranes

*adaptation for low temp

• syn mroe flexible proteins - weaker/less bonding

Question 4

what is the key concern with changes with env pH

Answer 4

• plasma memabrane is a permeability barrier and has the ETC to generate PMF (energy generation)
• without proton motive force - no coupled transport, no flagellar rotations and no ATP synthase

Question 5

relationship between membrane and cytoplasm to pH

Answer 5

• membrane of alkophiles or acidophiles mebrane is leaky under extreme pH condiitons
• cytoplams is maintained at approx near neutral pH due to ill defined active transprot

*issue is external environment - problem for proteins on the plasma membrane: want to prevent denaturation

Question 6

what is A. ferrozidans

Answer 6

aka rustry

• acidophile
• ithotroph that uses sulfur and iron as energy source (a lot of acidophiles create their own acidic environemtn)

Question 7

what is natronobacterium

Answer 7

-alkaliophile

Question 8

what is a concern at high pH

Answer 8

• hydrogen bonds that hold DNA toether can break and lipids are hydrolyzed

Question 9

describe the adaptations to high pH and low pH

Answer 9

high pH: alkaline shock proteins to resist deprotonation

lower pH: acid shock prtoeins, more flexible and resistant to protonation

*neutrophiles have a global stress response - induction of acid/alkaline-shock proteins (chaperones) to protect against denaturation and help refold proteins

Question 10

just note: survival does not make an organism an extremophile!

• can surive but not grow (like ecoli surviving the stomach)

Question 11

describe acidophiles

Answer 11

• grow optimally below pH 5
• membrane is slightly leaky to protons, the cytoplasmic pH is usually only slightly acidic bc can actively trasnport h+ ions out of the cell
• cytoplasmic proteins have evolved to function at slighlty acidic pH with increased negative surface charges compared to neutrophiles

*many are archea

• their proteins have secondary, tertiary and quaternary structutes that are resistant to protonating effects of the acidic environment

Question 12

what makes archeal membranes advantageous for alkaliphilesand acidophiles

Answer 12

archea are typically the most successfl extremeophiles

• ether linked which is more stable to acid
• can fold a tetraether membrane lipid, onolayer structure makes memrbanes much better barrier to proton leakage @ very low pH

Question 13

describe alkaliphiles

Answer 13

• have diether lipid membranes: ether linkage is more resistant to chemical or thermal degredation compared to ester linked phospholipids
• cell surface has high concentration of acidic (neg cahrged) molecules - acts as a proton spronge allowing more rapid lateral diffusion of proteins from ETS to ATP synthase
• secretes proteins the have evolved to resist deprotonation/denaturation and chemical degredation at high pH
• maintaining PMF is biggest challenge so have adapted a aodium motive force

-

Question 14

decribe the sodium motive force

Answer 14

• N+/H+ antiport can create sodium motive force
• energy derived for reactions and motility can be form SMD rather than PMF (utilized in Bacillus firmus)
• can also use SMF to conserve protons for ATP synthase and use SDM for flagellar rotation

Question 16

what is Bacteriorhodspin

Answer 16

protein used by Archaea -esp haloarchaea

acts as a proton pump to captures light energy and uses it to move protons across the membrane out of the cell

The resulting proton gradient is subsequently converted into chemical energy

Question 17

correlation between salinity of env and ability to use SMF

Answer 17

NO CORRELATION between use of SMF with adaptation to increase [NaCl]

Question 18

what is water activity

Answer 18

available moisture

• 1/osmolarity

Question 19

how is plasmmolysis avoided?

Answer 19

• plasmolysis = cell shrinks in yhpertonic solution
• active transport of compatible solutes like K+ to facilitate adaption to changes in osmolarity of a cell’s environment
• release via mechanosensitive channel

**remember that K+ is compatibel solute

Question 20

how do cells aovid osmotic lysis

Answer 20

• rigid bacterial/archeal cell wall prevents it
  note: lysozyme and antibiotics that target PG crosslinking (B lactams, vancomylin) lead to osmotic lysis (lethal efefct of the drugs)
• mechanosensitive membrane channels release solutes under osmtoic stress to inc tugor pressure

Question 21

how do microorganisms grow in such nutrient sparse areas?

Answer 21

• Psychrophilic bacteria & algae may grow in brine veins within ice and snow - halophilic psychrophiles

^- many are photosynthetic that abs light energy can ause heat and local areas of melting

*as water molecules interact while water freezes, any solutes get squeezed out of ice crystal lattice

Question 22

halophiles vs extreme halophiles

Answer 22

• oceans are 3.5 NaCl so marina bacteria and archea are halophiles
• some env are highly salty and find extreme halophiles: salterns, great salt lake and dead dea
• can isolate halobacterium salinarum in these en: VERY halphilic and contain bacteriohodospin so are red
• extreme halophiles are volutionarily distinct gorup of archea, absolute requrement for 13-15% salt