Ion beambiotechnology has recently been rapidly developed [1]. The
technology utilizes ion beams normally at energy as low as an order of
10 keV to irradiate biological organisms to induce mutation and gene
transformation for applications in biology and agriculture [1–3]. In contrast
to plentiful and significant successes in applications, many fundamentals
remain unclear in this subject. For ion beam induction of
mutation, general questions include how DNA inside the cell nucleus is
interacted by the low-energy ions and howDNA is changed by the interaction.
It has been proposed that both direct and indirect effects from ion
beam irradiation are involved in the ion interaction with DNA [1]. Thedirect
effect refers to direct interaction between incident ions and DNA in
terms of atomic collisions and the indirect effects refer to productions
of ion beam induced secondary electrons, X-ray, heat and free radicals,
all ofwhich are potential agents to interactwith DNA to cause certain degree
change in DNA.Wehave focused our interest in the direct effect. Experiments
have observed and investigated abnormal great range and
sputtering of the low-energy ions in biologicalmaterials [1,4], predicting
a small number of incident ions able to penetrate through the materials
that cover the cell nucleus to interact with DNA. In this case, the energy
of the ions must be fairly low. Moreover, energy deposition from
implanted ions, no matter with what energy, dominantly occurs around
the Bragg peak which is immediately before the ion comes to the rest,
and implanting ions recoiled atoms can also interact with DNA. In both
cases, the energy of the interacting ion is low. In order to study the direct
low-energy ion bombardment effect on DNA, we have introduced lowenergy
ion beams or plasma ions to bombard naked plasmid DNA to investigate
relevant effects on DNA conformation change and subsequent
mutation in bacteria [5,6]. The ion energy as low as an order of keV has
been found to be able to induce DNA conformation change from natural
supercoils to relaxed and linear forms and mutation of the DNA transformed
bacteria. In this study we further investigated details of plasma
low-energy ions bombarded extracellular DNA of a smaller plasmid
than that used before with a higher sensitivity to the ion irradiation
and induced mutation of the DNA transformed bacteria. The details included
the relationships between the mutation frequency and the deposited
ion energy, identification of the location of the DNA damage which
should be responsible for the mutation induction and DNA lesion
characteristics.