Physiological properties of a Pseudomonas strain which grows with p-xylene in a two-phase (organic-aqueous) medium

Abstract

Pseudomonas putida Idaho utilizes toluene, m-xylene, p-xylene, 1,2,4- trimethylbenzene, and 3-ethyltoluene as growth substrates when these hydrocarbons are provided in a two-phase system at 5 to 50% (vol/vol). Growth also occurs on Luria-Bertani medium in the presence of a wide range of organic solvents. The ability of the organism to grow in the presence of organic solvents is correlated with the logarithm of the octanol-water partition coefficient, with dimethylphthalate (log P(OCT) = 2.3) being the most polar solvent tolerated. During growth with p-xylene (20% [vol/vol]), there was an initial lag period accompanied by cell death, which was followed by a period of exponential growth. The stationary phase of growth was characterized by a dramatic decrease in cell viability, although cell dry weight and turbidity measurements slowly increased. Electron micrographs revealed that during growth in the presence of p-xylene, the outer cell membrane becomes convoluted and membrane fragments are shed into the culture medium. At the same time, the cytoplasmic membrane invaginates, forming vesicles, and becomes disorganized. Electron-dense intracellular inclusions were observed in cells grown with p-xylene (20% [vol/vol]) and p-xylene vapors, which are not present in cells grown with succinate. Attempts to demonstrate the presence of plasmid DNA in P. putida Idaho were negative. However, polarographic studies indicated that the organism utilizes the same pathway for the degradation of toluene, m-xylene, and p-xylene as that used by P. putida mt-2 which contains the TOL plasmid pWWO. Southern hybridization experiments showed that P. putida Idaho contains regions of DNA that are homologous to genes encoding enzymes of the upper operon in the TOL plasmid pWWO.