Transcriptional Control of the Expression of a Degradative Plasmid in Pseudomonas
Considerable attention has recently been directed toward studying the genetic basis of nutritional versatility in Pseudomonas. Unlike the enterobacteria, which grow on a limited number of complex organic compounds, the genus Pseudomonas is known for its ability to derive its carbon and energy from the dissimilation of a large number of organic compounds of varying complexities (1). The genetic and physiological regulation, the enzymology, and the biochemistry of a large number of catabolic pathways have therefore been extensively studied in this genus (2). The ability of the pseudomonads to degrade a number of complex organic compounds has been recently shown to be due to their possession of extrachromosomal elements that specify the entire enzyme complements of a particular degradative pathway. Thus the genes specifying enzymes responsible for the degradation of salicylate in a strain of Pseudomonas putida R1 are not part of the bacterial chromosome but are borne on extrachromosomal elements which are transmissible among a number of Pseudomonas species (3). Similarly, the camphor degradative pathway, comprised of a set of 15-20 inducible enzymes, is specified by genes that are also part of a transmissible plasmid (4). Another set of genes that code for enzymes responsible for the metabolism of octane is carried on yet another transmissible plasmid (5). We have proposed to term these naturally occurring plasmids “degradative plasmids” because of the selective nutritional advantage they offer to the host cells harboring them (6).
KeywordsFiltration Bromide Pyruvate Pseudomonas Ethidium
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