Chromosome Transfer in Proteus Mirabilis Mediated by a Hybrid Plasmid

Abstract

A previously-described fused plasmid, P-ZacR 1drd19, was found to mediate chromosomal transfer between cells of Proteus mirabilis strain ~~5 0 0 6; ~~5 0 0 6 -(P-ZacRrdrd19) was usually the donor and various auxotrophs of ~~5 0 0 6 resistant to nalidixic acid and/or streptomycin were recipients. The donor was usually counterselected with nalidixic acid and/or high concentrgtions of streptomycin. Recombination experiments with single markers indicated a 40-fold variation in recombination frequencies for different markers. Mapping double-auxotrophic markers by their gradient of transmission confirmed this variation and placed each of two independent isolates of eight markers in a linkage group his-ser-ura-pyrBtrp-cys-ade-ilv. Some donor markers did not register. Despite low recombination frequencies, interrupted mating experiments showed a polarity of early marker transfer. The segregation of unselected markers confirmed the order of some markers and showed that genetic material passed from the presumptive donor to the recipient. Recipients with two auxotrophic markers which could not be cotransduced by phage 5006M were converted to prototrophy by conjugation. The plasmid transferred to recipients at high frequency and all recombinants carried it. Recombinants could act as donors in further matings. Recombinants were fully susceptible to phage 5006M, unlike transductants of ~~5 0 0 6 by this phage. Direct involvement of the plasmid was indicated by drastically diminished recombination frequencies in crosses with recipients carrying P-lac as resident. P-lac had previously been shown to reduce the frequency of transfer of the hybrid plasmid to cells harbouring it. The histidine region was the first to register in recipients and recombined at the highest frequency of 5 x Io-6/donor cell. Some temporary association of plasmid and perhaps only the histidine region of the chromosome is favoured as the mechanism of chromosomal transfer. This could explain why not all donor markers could be mapped. Transduction and transformation were excluded as the cause of results.

Extension of a Chromosome Linkage Group of Proteus mirabilis

“…To cover a range of markers, separate experiments were done with up3 (his-I), up4 (pyrBl) and up12 (ade-l) as recipients and u~7 7 ( D ) [argE2 tyr-l str-l (D)] as donor. In fluid matings (Coetzee, 1975), recombinants for the his, p y B and ade markers involved were recovered at about 5 x lo+, 1 x per donor cell and 2 x 158 J . N COETZEE respectively.…”

“…1) and a gradient of transmission existed with respect to p y B + recombinants used as internal standard (Table 3). Also alleles of markers arg-1 , leu-1 and met-1 [subsequently identified as being argAl, ZeuBl and metF1 (unpublished results)], which had failed to produce recombinants previously (Coetzee, 1975), now registered in experiments (Fig. 1).…”

“…Chromosomal markers not studied before (Coetzee, 1975) were mobilized by plasmid D (Fig. 1) and a gradient of transmission existed with respect to p y B + recombinants used as internal standard (Table 3).…”

“…Selection was for recombinants of the (presumed) distal markers of the first group, and then the proportion which had also incorporated the proximal-ilv-2 marker was determined. The markers could thus be arranged in the sequence ilv-2, cysG1, gly-1, Pro t e us ch rom osome transfer 159 (Coetzee, 1975) and the present extension, respectively. Markers are arbitrarily spaced.…”

“…On the basis of the recovery of recombinants listed in Table 3, the markers were divided in two groups; up48 (tyr-2) and up49 (argEl), markers which had failed to yield recombinants (Table 3), were incorporated in both groups. Markers of the first group were tested for linkage to ilv-2 the most distal marker previously recorded (Coetzee, 1975). Selection was for recombinants of the (presumed) distal markers of the first group, and then the proportion which had also incorporated the proximal-ilv-2 marker was determined.…”