10. Extremophiles I

Question 1

what is an extremophile?

Answer 1

• organism that thrives under extreme conditions
• anthropocentric term, judged based of human extreme

Question 2

what examples of extremophiles are there?

Answer 2

• thermophiles
• psycrophiles
• acidophiles
• alkaliphiles
• halophiles
• piezophiles
• polyextemophiles (themophilic acidophile)

Question 3

what is th challenge of life at high temperatures?

Answer 3

• denaturation

Question 4

what organism lives at extreme hot temperatures?

Answer 4

• thermophilic
• habitat in excess of 40 degrees
• geological thermal sites (volcanoe, hot spring, deep-sea hydrothermal vents)

Question 5

what are the types of thermophiles?

Answer 5

• psychrophile
  – grow at 0 and below; optimum at 15
• mesophile
  – optimum from 20 - 45
• thermophile
  – optimal growth at 40 or over
• hyoerthermophile
  – optimal at 80 or over

Question 6

how have thermophiles adapted to live at high temperatures?

Answer 6

• stabilisation of membrande fluidity (increasing fatty acid chain length and branching)
  – presence of sat. fatty acids in membrane lipids
  – sat. fatty acids form stronger hydophobic environment helping membrane stability
• higher amount of cystine amino acids (form disulfide bonds)
  – critical amino acid substitutions allowing folding increasing heat stability
• genes coding for HSP60 proteins (refold unpregulated proteins)

Question 7

what are the consituents of psycrophiles? **

Answer 7

• optimum growth at 15
  – usually inhibit at low temperatures
• eg..

Question 8

what are the psycrophilic adaptations?

Answer 8

• lipid membranes more unsaturated fatty acids
  – more fluid
• upregulation of cold/heat-shock protein expressions
• accumulation of cryoptotectants
  – glycine; betaine; glycerol; trehalose; sucrosel mannitol; sorbitol
  – cryoprotectants reduce freezing pt. of cytoplasm
  – prevent macromolecule aggregation
  – scavenge free radicals and stabilise cellular membranes under cold conditions

Question 9

what are acidophiles?

Answer 9

• have optimum pH less than 3 for growth
• live in acidic environments

Question 10

what are acidophiles role in sulfur cycling and acid mine drainage?

Answer 10

• Ferroplasma
  – pH = 0
  – use sulphur cycling to transform sulphide from metal ores to sulphuric acid

Question 11

how have acidophiles adapted?

Answer 11

• reverse membrane potential to partially deflect inward flow of protons
  – potential mechanism of generating reversed membrane potential is by potassium transport
  – predominance of potassium-transporting ATPases found in genomes
• evolved highly impermeable cell membranes to retard influx of protons inot cell
  – increased membrane rigidity by increasing no. of longer chained fatty acids across lipid bilayer
  – and lipid order, chain saturation, cyclization, and hopanoids
• pH gradient maintained through active proton export by transporters
• sequencing of several genome sequences
  – higher proportion of secondary transporters in neutralophiles
  – reduce energy demands of pumping necessary solutes and nutrients into cell
• cytoplasmic buffers
  – contain basic amino acids to keep pH constant and neutralise acidic effect
• presence of enzymes/chemicals capable of bidning and sequestering protons
• larger proportion of DNA and protein repair systems present

Question 12

what are alkalophilic organisms?

Answer 12

• pH > 9

Question 13

what are the effects of high pH on organisms?

Answer 13

• membrane damage
• DNA damage
• lowered enzyme activity

Question 14

how have cells adapted to high pH conditions?

Answer 14

• elevated levels of transporters and enzymes
  – promote proton capture and retention
• metabolic changes
  – lead to increased acid production

Question 15

what are halophiles?

Answer 15

• hypersaline conditions (salt >3,5%)

Question 16

how have organisms adapted to hypersaline conditions?

Answer 16

• high intracellular concentrations of potassium (4-7 M)
  – remain hypertonic to external environment
• compatible solutes
  – small organic molecules acting as osmolytes (not interfering with metabolic fxns)
  – eg.) glycine, proline, trehalose
  – provide osmotic balance, does not require interal high salt ion concentration

Question 17

how have microbes adapted to hypersaline intense ultraviolet radiation?

Answer 17

• effecient DNA repair
• mechanisms to prevent damage
  – eg.) halophillic archaea have low number of UV targets (thymines) in genome
• colourfoul carotenoids
  – class of important antioxidants providing protection from UV damage

Question 18

what are piezophiles?

Answer 18

• optimum growth at >40 MPa
  – low temperatures, high pressures

Question 19

how have piezophiles adapted?

Answer 19

• membrane fatty acid alterations
  – increased unsaturation, chain length and ratio of branching
• chaperone proteins are upregulated
  – maintain proper folding and fxn of proteins
• membrane proteins (OmpL & OmpH)
  – porins that regulate growh under high pressure

Question 20

what are radiophiles?

Answer 20

• resistant to ionising radiation

Question 21

what is an example of a radiophile?

Answer 21

• deniococcus radiodurans
  – capable of withstanding acute 5000 gray ionizing radiation
• developed 2 stage mechonism to re-assemble genome after beig shattered by double stranded breaks
• highly accurate in rejoining DSB fragments correctly
  – related to extreme resistance to desiccation