This phenomenon is one of the check details major mechanisms of HGT (Llosa & de la Cruz, 2005). According to their transfer ability, conjugative plasmids may be grouped into two categories comprising self-transmissible or mobilizable replicons. The self-transmissible plasmids contain two DNA regions: (1) MOB, which carries genetic information essential for the processing of conjugative DNA, and (2) mating pair formation (MPF), encoding a membrane-associated complex, which is a type 4 secretion system that forms the mating channel (Smillie et al., 2010). Mobilizable plasmids carry only the MOB

module, and their transfer requires an MPF provided by another genetic element co-residing in the cell, that is, a self-transmissible plasmid or integrative and conjugative element, ICE (Smillie et al., 2010). MOB systems are highly conserved and widespread among plasmids (including small cryptic types) commonly found in bacterial isolates (e.g. Bartosik et al., 2002). In this study, we analyzed three small cryptic NHR plasmids (pIGMS31, pIGMS32, and pIGRK) of a pathogenic strain of Klebsiella pneumoniae. The analyses revealed that the plasmids

contain different MOB modules, which function in a wide range Venetoclax order of hosts. This strongly suggests that NHR mobilizable plasmids (similarly as BHR replicons) may play a very important role in the dissemination of genetic information in HGT. Klebsiella pneumoniae 287-w (isolated from the throat of an infant hospitalized in The Children’s Memorial Health Institute in Warsaw) was the host strain of the plasmids pIGMS31, pIGMS32, and pIGRK. The following Escherichia coli strains were employed: (1) DH5α, in plasmid construction (Hanahan, 1983); (2) DH5αR (rifampicin resistant), as a recipient in bi-parental mating (Bartosik et al. 2002); (3) NM522, as a host for plasmids in in vitro transposition (Stratagene); (4)

S17-1, as a donor in bi-parental mating (Simon et al., 1983); and (5) TG1, in plasmid construction. The following rifampicin- or Thymidylate synthase streptomycin-resistant strains were used in the host range analysis: (1) Agrobacterium tumefaciens LBA1010 (Rifr; Koekman et al., 1982); (2) Brevundimonas sp. LM18R (Rifr); (3) Paracoccus aminovorans JCM 7685 (Rifr); and (4) Rhizobium etli CE3 (Strr; Noel et al., 1984) – all members of the Alphaproteobacteria; as well as (4) Serratia sp. OS9 (Gammaproteobacteria; Drewniak et al., 2008, 2010). Bacteria were grown in lysogeny broth (LB) medium (Sambrook & Russell, 2001) or TY medium (R. etli) (Beringer, 1974) at 37 °C (E. coli) or 30 °C (other strains). When necessary, the medium was supplemented with antibiotics at the following concentrations: ampicillin – 100 μg mL−1; kanamycin – 50 μg mL−1; rifampicin – 50 μg mL−1; streptomycin – 50 μg mL−1 (E. coli S17-1) or 100 μg mL−1 (R. etli CE3); and tetracycline – 20 μg mL−1. The plasmids used in this study are listed in Table 1.