The TOL catabolic plasmid was shown to be compatible with the R91 drug resistance plasmid. However, the TOL plasmid was extremely unstable in mutant PA03 of P. aeruginosa. By selecting for stabilization of the TOL plasmid in PA03 harbouring R91, it was possible to isolate a strain in which markers from both R91 and TOL appeared to exist in a single recombinant plasmid. This plasmid, pND3, encoded resistance to carbenicillin, was able to transfer at the same frequency as the R91 plasmid and encoded the ability to grow on m-toluate, p-toluate, m-xylene, p-xylene and toluene. In addition, it was shown to be incompatible with the NAH catabolic plasmid and it could be transferred by transduction. The TOL plasmid could stabilize in PA03 harbouring R91 without fusion with R91, and could stabilize in PA03 in the absence of R91. PA03 harbouring either the recombinant plasmid or the stable TOL plasmid in the absence of R91 could promote bacterial chromosome transfer between mutant derivatives of P. aeruginosa strain P AO.

The investigation of chelating agents with potential therapeutic value in patients with transfusional iron overload has been facilitated by the use of Chang cell cultures. These cells have been incubated with [59Fe]transferrin for 22 hr, following which most of the intracellular radioiron is found in the cytosol, distributed between a ferritin and a nonferritin form. Iron release from the cells depends on transferrin saturation in the medium, but when transferrin is 100% saturated, which normally does not allow iron release, desferrioxamine, 2,3- dihydroxybenzoic acid, rhodotorulic acid, cholythydroxamic acid, and tropolone all promote the mobilization of ferritin iron and its release from cells. They are effective to an approximately equal degree. The incubation of [59Fe]transferrin with tropolone in vitro at a molar ratio of 1:500 results in the transfer of most of the labeled iron to the chelator, reflecting the exceptionally high binding constant of this compound. How far these phenomena relate to therapeutic potentially remains to be seen.

The sex specific bacteriophage PR4 has been found to plate on P. aeruginosa strains harbouring the TOL catabolic plasmid or the plasmid pND2 derived from TOL. Based on this, attempts were made to place TOL into a Psevdomonas plasmid incompatibility group and by showing that pND2 is incompatible with the R plasmid R2, TOL has been placed into the P-9 group. The NAH catabolic plasmid has been reported to be incompatible with TOL, pND2 and a variety of other plasmids derived from TOL. Thus, these plasmids also would appear to belong to the P-9 incompatibility group. 15-2

The previously isolated plasmid pND3, arising from recombination between the TOL catabolic plasmid and the R plasmid R91, was transduced by pfl6 in Pseudomonas putida. Apparent transductional shortening was evident in 25 % of the transduced pND3 plasmids. Transductants were isolated which had segregated the antibiotic resistance marker, transfer ability and some of the catabolic functions of the parent plasmid. INTRODUCTIONWe are conducting a study aimed at increasing the transfer range of the TOL catabolic plasmid. One method being employed is to attempt in vivo fusion with several R plasmids. Ideally it is desirable to obtain a recombinant plasmid which carries the catabolic information of the TOL plasmid, the transfer information of the R plasmid and which has had resistance to the antibiotics deleted.We recently reported the isolation of a plasmid (pND3) which arose from apparent recombination between the TOL catabolic plasmid and the R91 R plasmid (White & Dunn, 1977). This recombinant plasmid encodes for the degradation of m-toluate, p-toluate, m-xylene, p-xylene and toluene, as does the parent catabolic plasmid, and encodes carbenicillin resistance from the R plasmid. Furthermore, pND3 is incompatible with the NAH catabolic plasmid, is able to mediate its own transfer and promote transfer of the bacterial host chromosome and carries at least the plasmid transfer system of R91. pfl6 mediated transductants could be readily obtained in which all encoded properties could be cotransduced. However a significant proportion had lost at least one phenotypic property, probably as a result of transductional shortening. This paper describes the transductional shortening data.

No abstract