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Question 1

rotifers

Answer 1

The rotifer’s resistance to desiccation and radiation may also provide clues to human aging and disease
Protection from radiation in other organisms comes from a robust defense against reactive oxygen species, which damage DNA and is linked to aging.
It is likely that rotifers have developed a super-scavenger that mops up reactive oxygen species

Question 2

Unique features of Deinococcus radiodurans?

+toilerating mechanisms

Answer 2

It is equally susceptible to DSB as sensitive bacteria  not resistant BUT able to repair more efficiently

Tolerating mechanisms:

Multiple genome
multiple gene copies
template for repair

Genome organisation
circular structure
condensed genome

Question 3

RecA protein

Answer 3

(repair process)

RecA protein
Binds DNA duplex first and single strand second
Normally other way around

Question 4

ESDSA and RecFOR Pathway

Answer 4

Extended Synthesis-Dependent Strand Annealing (ESDSA)
Explains rapid and correct reassembly of shattered genome
RecFOR pathway
Used instead of RecBCD
Initiates ESDSA and DSB repair
No unique proteins used in repair process

Question 5

D. radiodurans

Answer 5

D. radiodurans are less susceptible to oxidative protein damage resulting from radiolysis of H2O to generate ROS
Proteins able to repair radiation damage in DNA
Higher levels of manganese (Mn2+ ) than IR sensitive bacteria
Actively transports Mn2+ into cells
Mn2+ protects proteins from IR induced Reactive oxygen species (ROS)
Do not reduce level of DNA damage

Question 6

Geobacter uraniireducens

Answer 6

Geobacter uraniireducens Rf4 reduces metals including uranium with acetate and other organic acids serving as the electron donor.
Geobacter expressing pili removed more uranium from a solution than those without pili
Gains energy for growth by transferring electrons generated inside the cell to external electron acceptors
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Question 7

Radiation resistant fungi

Answer 7

Accidentally discovered black fungi growing in Chernobyl

Enhanced growth when exposed to ionizing radiation

They accumulate high levels of melanin

Question 8

Fungi and Melanin

Answer 8

Melanized fungi are highly resistant to IR
E.g. Cryptococcus neoformans
Inhabit environments with high levels of IR
High altitude, Chernobyl power plant, orbiting in space
Food/Medical irradiation dose is 1kGy – melanized fungi can survive this
Melanin is dark, high molecular weight pigment
Eumelanin - black/dark brown
Pheomelanin – reddish/brown
Concentrated in cell wall – spherical layers

Melanin is the key to radiation resistance

Question 9

Radioprotective properties of melanin

Answer 9

Spherical spatial arrangement provides radioprotection
non-spherical melanin conferred no protection
Traps electrons formed due to IR
Stable free radical population
Change in the ESR (electro spin resonance) = melanin is able to trap electron and protect cell
Transfers electrons
Irradiation of melanin increased the NADH/ferricyanide coupled reaction
Enhances growth
Irradiated cells grew faster and had a greater biomass

Question 10

Mycoremediation after radioactive fallout

Answer 10

Hymenoscyphus ericae can accumulate uranium as a phosphorous precipitate

Radioactive uranium can be safely stored

Currently considered for Fujiyama nuclear accident

Question 11

Geobacter metallireducens

Answer 11

Ability to directly transfer electrons to the surface of electrodes
Provide a model for important iron transformations on modern earth and may explain geological phenomena, such as the massive accumulation of magnetite in ancient iron formations
Applications- production of electricity

Question 12

Geobacter sulfurreducens

Answer 12

Can use H2 as electron source, but no organics
Alternate e- acceptors: 
Co(III)
Sulfur
Malate
Fumarate

Question 13

Central problem: How to reduce insoluble Fe(III)?

Answer 13

Geobacter
Requires direct contact
No evidence for secretion of electron shuttles or chelators
Can reduce soluble (chelated) Fe(III), but likely requires special mechanisms to reduce ferrite.
Cytochromes on outer membrane important

Question 14

Shewanella oneidensis

Answer 14

Anaerobic bacteria which is predominantly found in rocks and deep sea anaerobic habitats
Reduce heavy metals in the environment via cytochromes secreted on the outer membrane
Applications-bioremediation
Anaerobic bacteria which is predominantly found in rocks and deep sea anaerobic habitats
Reduce heavy metals in the environment via cytochromes secreted on the outer membrane
Applications-bioremediation

Question 15

reducing insoluble FEIII shewanella

Answer 15

Does not require direct contact
Secretes electron shuttles (quinones) to reduce Fe(III) to Fe(II).
Secretes chelators to solubilize Fe(III)
This may be a good strategy if cell density is high.

Question 16

Presence of Arsenate in the DNA of GFAJ-1

Answer 16

Life is mostly composed of the elements carbon, hydrogen, nitrogen, oxygen, sulfur and phosphorus.
Although these six elements make up the bulk of living matter, it is theoretically possible that some other elements could serve the same functions.
Halomonadacea bacteria GFAJ-1, isolated from Mono Lake, substitutes arsenic for phosphorus to sustain its growth.
Nucleic acid and proteins of GFAJ-1 contain arsenate instead of phosphate.