Figure 3 : Transfer of a resistance gene from actinobacteria to proteobacteria by the ‘carry-back’ model.

From: Dissemination of antibiotic resistance genes from antibiotic producers to pathogens

Figure 3

Actinobacterial and proteobacterial cells are marked in red and blue, respectively. DNA sequences of actinobacterial and proteobacterial origins are likewise labelled in red and blue. Dashed line represents DNA that can be either a fragment of a chromosome or a plasmid. The terminal inverted repeats of cmx transposon are represented by red bars. (a) The proposed ‘carry-back’ interphylum gene transfer mechanism. (b) Examples of actual sequences found in different bacteria that resemble the proposed intermediates: (1) carrier sequence in proteobacteria; (2) carrier sequence in actinobacteria; (3) sandwich structure with cmx transposon flanked by carrier sequences in actinobacteria; (4) cmx transposon incorporated into genome in proteobacteria. Double-slash indicates additional resistance genes and mobile elements inserted into the proposed intermediate structures. NCBI accession numbers of these intermediate sequences are provided in Supplementary Data 4. (c) Experimental reconstruction of the interphylum gene transfer of cmx from actinobacteria to proteobacteria. C. resistens DSM 45100 naturally carries the sandwich structure. Plasmid pXJ83 is constructed by cloning the carrier sequence from P. aeruginosa BM4530 onto pUCP24 vector. *Kanamycin (kan) instead of chloramphenicol was used for the selection plates. Kanamycin resistance is coded by Tn5393e inserted in the cmx transposon. (d) Efficiency of natural transformation using A. baylyi ADP1/pXJ83 as recipient strain (error bar: s.d.; n=3). A. baylyi ADP1/pUCP24 was used as a negative control. The detection limit is one transformant per 109  colony-forming unit (c.f.u.) of recipient cells. ND, not detected. (e) Colony PCR of transformants using primers that target cmx. C. resistens DSM 45100 was used as a positive control. A. baylyi ADP1/pXJ83 was used as a negative control.