Novel narrow-host-range vectors for direct cloning of foreign DNA in Pseudomonas

Resistance to tellurite as a selection marker for genetic manipulations of Pseudomonas strains

Resistance to the toxic compound potassium tellurite (Telr) has been employed as a selection marker built into a set of transposon vectors and broad-host-range plasmids tailored for genetic manipulations of Pseudomonas strains potentially destined for environmental release. In this study, the activated Telr determinants encoded by the cryptic telAB genes of plasmid RK2 were produced, along with the associated kilA gene, as DNA cassettes compatible with cognate vectors. In one case, the Telr determinants were assembled between the I and O ends of a suicide delivery vector for mini-Tn5 transposons. In another case, the kilA and telAB genes were combined with a minimal replicon derived from a variant of Pseudomonas plasmid pPS10, which is able to replicate in a variety of gram-negative hosts and is endowed with a modular collection of cloning and expression assets. Either in the plasmid or in the transposon vector, the Telr marker was combined with a 12-kb DNA segment of plasmid pWW0 of Pseudomonas putida mt-2 encoding the upper TOL pathway enzymes. This allowed construction of antibiotic resistance-free but selectable P. putida strains with the ability to grow on toluene as the sole carbon source through an ortho-cleavage catabolic pathway.

Recombinant DNA techniques for bioremediation and environmentally-friendly synthesis

A number of new recombinant DNA techniques have been developed for genetically engineered microorganisms for biodegradation of environmental contaminants or for the synthesis of small molecules. These techniques include new expression vectors to carry the heterologous genes into the host organism, new mechanisms to control gene expression, containment mechanisms to control persistence of genetically-engineered microorganisms, application of site-directed and random mutagenesis to increase the substrate range or activity of biodegradative enzymes, and methods to track genetically-engineered microorganisms.

Stage-specific transcription of the homebox gene Bnhd1 in young tissues and flowers of Brassica napus

The Bnhd1 cDNA, only distantly related to published homebox gene sequences, was isolated from Brassica napus by the polymerase chain reaction. The Bnhd1 transcript was detected in all organs of young seedlings, but only in the youngest leaves and flowers of mature plants. A 4- and 7-fold increase in transcription levels was observed after wounding of young roots and leaves, respectively.