Archaea 2

Question 1

what does it mean to be an extreme halophile?

Answer 1

They are not only halophillic, but they require a high salt content to live

Question 2

when is an organism considered an extreme halophile?

Answer 2

When they need at least 1.5 M (9%) of sodium chloride (NaCL) for growth

Question 3

How much salt do most species need for optimal growth?

Answer 3

between 2-4 M (12-23%) NaCL

Question 4

At which high salinity can they still grow, and what is the speed at that level?

Answer 4

5.5 M (32%) -> which is the limit for NaCl saturation. they grow slowly at this salinity

Question 5

Salt lakes can be extremely productive ( a word that here means a high level of autotrophic CO2 fixation) - In the absence of Dunaliella, which bacteria dominate?

Answer 5

anoxygenic phototrophic purple bacteria

Question 6

What type of energy sources are haloarchaea?

Answer 6

chemoorganotrophs: they need chemical energy in the form of organic compounds -> containing either a CH or CC bond

Question 7

When do marine salterns turn a reddish-purple colour and why?

Answer 7

if the limit is reached for haloarcharaea to live there. They turn that colour due to massive growth of haloarchaea cells. the red colour originates from cartenoids

Question 8

why are haloarchaea sometimes called halobacteria?

Answer 8

Halobacterium is the best studied genus of extreme halophiles, but this was prior to the discovery of Archaea.

Question 9

how do genera of Natrialbales, including Natronobacterium, Natronomonas, differ from other extreme halophiles?

Answer 9

They are additionally also extremely alkaliphilic.

Question 10

Where do natronobacterium live?

Answer 10

Soda lakes

Question 11

At which conditions do natronobacteria live optimally

Answer 11

low magnesium concentrations and at high ph (9-11)

Question 12

Why do Haloquadratum form gas vesicles?

Answer 12

To allow them to float at the surface, as most extreme halophiles are obligate aerobes

Question 13

what is special about the plasmids of extreme halphiles?

Answer 13

they have the largest naturally occuring plasmids known. moreover the cellular DNA has a different G:C ratio than chromosomal DNA

Question 14

which electron donors do haloarchaea use?

Answer 14

amino or organic acids

Question 15

describe the metabolism of haloarchaea

Answer 15

they have electron transport chains with cytochromes. energy is conserved via the pmf arising from the electron chain

Question 16

can haloarchaea use anaerobic respiration?

Answer 16

Some species can grow anaerobically coupled to the reduction of nitrate or fumurate

Question 17

how do haloarchaea withstand the osmotic forces in their saline environments.

Answer 17

Haloarchaea accumulate potassium in the cytoplasmic cell while exporting sodium to extracellular space, thus balancing osmotic pressure.

Question 18

why do halobacterial cells die if insufficient Na+ is present?

Answer 18

Cell wall of halobacterium are composed of glycoprotein while stabilized by Na+. without sodium ions, the cell wall breaks apart and the cell lyses (dies)

Question 19

what are the characteristics of the cytoplasmic proteins of halobacterium?

Answer 19

they are highly acidic (K+), contain lower levels of hydrophobic amino acids and lysine, a positively charged basic amino acid,

Question 20

why do cyplasmic proteins of halobacterium contain such features?

Answer 20

the cytoplasm is highly ionic, more polar proteins would remain in the environment.

Question 21

why do some species of haloarchaea catalyze a light-driven synthesis of ATP

Answer 21

it supports slow growth under anoxic conditions. H. salinarum can grow to such densities that oxygen is completely depleted

Question 22

is chlorophyll present in halobacteria that perform the light-driven synthesis of ATP?

Answer 22

no. instead they contain different light sensitive pigments -> red and orange caretonoids.

Question 23

what are bacterioruberins?

Answer 23

pigments primarly involved in light-driven synthesis of ATP in haloarchaea.

Question 24

what is bacteriorhodopsin?

Answer 24

a protein that is synthesized by h. salinarium and some other archaea under low aeration conditions that is inserted into their cytoplasmic membranes. it has a carotenoid like molecule attached to it that can absorb light and move a a proton across the membrane

Question 25

why do cells of halobacterium change color?

Answer 25

as the growth of under high aerotion conditions switches to low aeration and light-driven synthesis is triggered, the retinal attached to bacteriorhodopsin gives it a purple hue. Thus, as bacteriorhodopsin is synthesized and placed in cytoplasmic membrane, the color changes from red-orange to a purple hue.