For the D. natronolimnaea strain cell types, survival curves start with a moderate slope, and with increasing energy and dose, the

slope correspondingly increases. Therefore, the efficiency per energy and dose increment increases as well. This can be understood in terms of the effectively of radiation induced mutations. At low check details energies and doses, only a few mutations are induced with a large spatial separation, and a considerable fraction of these mutations can be irradiated effectively. In contrast, at high energies and doses, the density of mutations increases, leading to an interaction of mutations and thus a reduced surviving fraction. Effect of different 12C6+ irradiation Geneticin on cell growth Following irradiation, serial dilutions of the cell suspension to be tested were prepared. Ten microliters of each dilution was inoculated into a 96-well plate containing 180 μL of the growth medium. For each dilution 10 replicates were Selleckchem S63845 prepared. Plates were incubated at 27°C for 96 hours as previously described. The cell concentration was determined using the Reed and Muench method [44]. In

each individual experiment, a cell culture was divided into aliquots and subjected to a predetermined set of irradiation doses, including no irradiation exposure. The aliquots were diluted in growth medium immediately after irradiation and plated in duplicate or triplicate [45]. For each experiment, the multiple platings of unirradiated (0 Gy) aliquots were counted and averaged to give the initial cell density in CFU mL-1. This value represented 85–100% cell growth of the strain and was used as a base level comparison for all irradiated aliquots of the same culture. Optical density (OD) measurement at 600 nm was used to monitor cell growth. Wherever necessary, samples were diluted to a final OD value

lower than 0.3 [46]. For all irradiation conditions examined, the concentrations of viable cells increased in an exponential fashion, followed by the typical stationary and death phases (Figure 2). Microdosimetry using 12C6+ ions for the mutagenesis of D. natronolimnaea svgcc1.2736 strains clearly shows an exponential decrease in the growth out rate from 85% (0 Gy), to approximately 27% (LET 120 keV μm-1, energy 90 MeV u-1 and a dose of 3.5 Gy) (Figure 2O). 113% (Figure 2J) at LETs (120 keV μm-1), energies (60 MeV u-1) and dose (2.5 Gy), to about 111% (Figure 2G) at LETs (120 keV μm-1), energies (45 MeV u-1) and dose (3.5 Gy), to about 97% ( Figure 2C) at LETs (120 keV μm-1), energies (30 MeV u-1) and dose (3.5 Gy). Interestingly, many survivors of the high-energy irradiation displayed a significant delay in growth and required extended incubation times to allow formation of measurable sized colonies. Many of the low-energy survivors, however, displayed significant growth acceleration and therefore required shorter incubation times to form macroscopic colonies [47].