, 2005; He et al.,

2006). As already noted above, RecA is RAD001 concentration not required for the stationary-phase mutagenesis in P. putida (Tegova et al., 2004). At the same time, nonhomologous end-joining (NHEJ), an essential pathway responsible for the repair of DSBs, composed of the DNA end-binding Ku protein and a multifunctional DNA ligase (LigD), has been identified recently in many prokaryotes including Pseudomonas species and mycobacteria (Pitcher et al., 2007a, b; Shuman & Glickman, 2007). DNA repair provided by the bacterial NHEJ system has been shown to be inaccurate, resulting in single nucleotide additions or deletions with various lengths at the break site (Gong et al., 2005; Malyarchuk et al., 2007; Stephanou et al., 2007). Recent studies with Mycobacterium smegmatis revealed that NHEJ mutant strains are more sensitive to ionizing radiation and desiccation during the stationary phase than the wild-type

strain (Pitcher et al., 2007b). In addition, NHEJ is required for the repair of artificially induced, I-SceI-mediated chromosomal DSBs in stationary-phase cells (Stephanou et al., 2007). In Bacillus subtilis, NHEJ is also growth phase regulated, contributing to DSBR only during the outgrowth of spores or in stationary-phase cells (Wang et al., 2006; Moeller et al., 2007; Simmons et al., 2009). Therefore, it would be important to study whether NHEJ could play a role in learn more stationary-phase mutagenesis in bacteria. These studies are currently in progress in our laboratory. There is no single mechanism for the generation of stationary-phase mutations in bacteria. Multiple factors Edoxaban including oxidative damage of DNA and proteins, other kinds of DNA damage, errors occurring during DNA replication and inefficiency of DNA repair may cause mutations. Additionally, DNA repair synthesis itself may be a source of mutagenesis

under the growth-restricting conditions of bacteria. Moreover, because bacteria differ in the content of DNA polymerases and DNA repair enzymes, several mechanisms that have not discovered with the E. coli model may become apparent in other bacterial species. Bacteria belonging to the genus Pseudomonas, which represents one of the most diverse and ecologically widely distributed groups of microorganisms, carry, similar to many other bacterial species, a different set of specialized DNA polymerases compared with that characterized in enterobacteria. There are also differences in DNA repair enzymes/systems whose connection with stationary-phase mutagenesis needs further exploration. I wish to thank R. Hõrak, M. Putrinš, S. Saumaa, K. Tarassova and M. Tark for their comments on the draft version of this manuscript.