Several distinctive properties of PRD1, an icosahedral plasmid-dependent phage, are described. The drug-resistance plasmid-dependent host range of PRD1 extends beyond the P incompatibility group and includes gram-negative bacteria containing plasmids of incompatibility groups N and W. PRD1 phage will infect pseudomonads and Enterobacteriaceae containing either a P or W incompatibility group plasmid. PRD1 adsorbs to the cell wall of R + bacteria and thus its infectivity indicates cell wall alterations by these drug-resistance plasmid groups. PRD1 nucleic acid is duplex DNA with an estimated molecular weight of 24 × 10 6 . The appearance of PRD1 in electron micrographs is suggestive of lipid content in addition to its buoyant density of 1.348 in CsCl and its sensitivity to chloroform. The latent period of PRD1 varies with the R + host bacterial strain used for growth of the phage.

The Salmonella mutation assay has been adapted to a number of experimental procedures used to characterize the chemical components and molecular mechanisms involved in the direct-acting mutagenicity of diesel particle extracts. The mutagens were found to be unreactive towards purified DNA. Mutagenic activity was decreased in nitroreductase-deficient bacteria and increased in the absence of oxygen, suggesting that bacterial enzymes active the mutagens. The extract was fractionated by thin layer chromatography using both normal and reverse phase silica gel plates. On normal silica plates, a separation was made between unsubstituted PAH, nitro-PAH and the more polar aromatic compounds. About a third of the mutagenic activity in the particle extract was recovered in fractions containing monosubstituted nitro-PAH compounds. The absorption spectra and reverse phase chromatographic properties indicate 1-nitropyrene is a predominant component but not the only mutagen in these fractions. The remaining activity was in the more polar fractions, and mutagenicity assays using anaerobic conditions and nitro-reductase-deficient bacteria suggest they contain other nitro-substituted compounds.

When Pseudomonas aeruginosa PAO1c or P. putida PPO200 or PPO300 carry plasmid pJP4, which encodes enzymes for the degradation of 2,4-dichlorophenoxyacetic acid (TFD) to 2-chloromaleylacetate, cells do not grow on TFD and UV-absorbing material with spectral characteristics of chloromaleylacetate accumulates in the culture medium. Using plasmid pRO1727, we cloned from the chromosome of a nonfluorescent pseudomonad, Pseudomonas sp. strain PKO1, 6- and 0.5-kilobase BamHI DNA fragments which contain the gene for maleylacetate reductase. When carrying either of the recombinant plasmids, pRO1944 or pRO1945, together with pJP4, cells of P. aeruginosa or P. putida were able to utilize TFD as a sole carbon source for growth. A novel polypeptide with an estimated molecular weight of 18,000 was detected in cell extracts of P. aeruginosa carrying either plasmid pRO1944 or plasmid pRO1945. Maleylacetate reductase activity was induced in cells of P. aeruginosa or P. putida carrying plasmid pRO1945, as well as in cells of Pseudomonas strain PKO1, when grown on L-tyrosine, suggesting that the tyrosine catabolic pathway might be the source from which maleylacetate reductase is recruited for the degradation of TFD in pJP4-bearing cells of Pseudomonas sp. strain PKO1.

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