The Role of Clays in Shielding DNA against X-Ray Radiation: Possible Implications on the origin of life Angela Ciaravella F. Scappini (2), M. Franchi (3),

The Role of Clays in Shielding DNA against X-Ray Radiation: Possible Implications on the origin of life

Angela Ciaravella

F. Scappini (2), M. Franchi (3), E. Gallori (3), C. Cecchi-Pestellini (4), M. Barbera (1),

R. Candia (1), G. Micela (1)

(1) INAF – Osservatorio Astronomico di Palermo , Italy

(2) ISMN –CNR , Bologna, Italy

(3) Dipartimento di Biologia Animale e Genetica, Univ. di Firenze, Italy

(4) Dipartimento di Fisica, Univ di Lecce, Italy

Firenze 28/02 – 1/03/05

First evidence of life on the Earth 3.8 × 109 yr

Earth Atmosphere :

a big unknow, very little screening from Sun radiation

Conditions on the Early Earth

Early X-ray Sun:

more active, hard and bright 3 × 1026 (0.1 keV)

< Lx > = 1027 erg/sec

5 × 1027 (0.2 keV)

Yohkoh-SXT 3-40 Å band

1-10 keV band:

the photon flux today is ~10-3 the flux at the age of Pleiades

Sun

@ m

inSu

n @

max

How and under which conditions life was created?

DNA Irradiation

Free DNA type B

Clay Adsorbed DNA type A

34 Å per turn B

27-28 Å per turnA

Why DNA? DNA is already life

An easy and well tested method to estimate damage

We irradiate free and clay absorbed DNA from Bacillus Subtilis

CLAYS: Montmorillonite Na0.2Ca0.1Al2Si4O10(OH)2(H2O)10

Kaolinite Al2Si2O5(OH)4

Vacuum tight container

X-ray, UV, Vis 2 -104 eV (1- 7000 A).

17 m stainless-steel vacum beam lineclass 1000 clean_room (Barbera et al 1999).

The XACT Facility:

Al 1.49 0.15 Ti 4.51 0.17 Cu 8.04 0.20

Flux (erg sec-1 cm -2 )

Line(keV )

DNA X-Ray Irradiation

Irradiation Dose : 102 - 5.8 × 104 ergExposure Time : 2m - 16h

10-5 minimum

3 × 10-3 maximum

10-1 large flares

The Sun today (1.5 –12.4 keV):

DNA Samples: Free 10μg DNA + 1400l of H2O Clay Adsorbed 10μg DNA + 2mg Clay + 1400l of H2O

DNA Damage Evaluation

The integrity of DNA molecules is estimated by transformation experiments :

efficiency of irradiated DNA to transform competent cell in a bacterial culture

for

Number of transformed bacterial cellsFtf =

Total number of bacterial cells

Comparing Ftf with Ftf0 the damage is evaluated

Typical errors on Ftf are 20 %

The transformation frequence is:

Transformation frequence for non irradiated DNA

Results and Conclusions I

*** Free DNA is severely damaged by X-rays

and the damage depends on the energy dose rather than the hardness of radiation

⃟ ⃟ ⃟ ⅏⅏ ⅏

Clay Adsorbed DNA is resistent to the X-ray irradiation

Can clays shield DNA against X-rays?Diluted clay is much more transparent than H2O to X-rays

The more compact configuration (A) of clay adsorbed DNA binding to the substrate by electrostatic and/or hydrogen bonds

can play protective role

Results and Conclusions II

Are X-rays directly responsible for DNA damage?

Num X photons (Cu 5 × 104 erg) 4 × 1012

Num H2O molecules 5 × 1022

Num DNA molecules 4 × 1011

Secondary UV

UV irradiation of free and clay adsorbed DNA give similar results (Scappini et al 2004)

2.5 mm

1 mm

0.2 mm

0.01 mm

Are clays essential in protecting the basic building blocks of life as well ?

DNA adsorbed on clays do survive X-rays and UV photodegradation