Greenhouse and field evaluations of an autoselective system based on an essential thymidylate synthase gene for improved maintenance of plasmid vectors in modified Rhizobium meliloti

Article Abstract:

The 'thy' autoselective system can efficiently maintain the stability of the plasmid vector in Rhizobium (R.) meliloti under field and greenhouse conditions, and can make thymidylate synthase-deficient (Thy-) rhizobia nodulate the host. But the expression of the thy gene needs to be regulated to avert its negative effects on symbiosis. The thy system is based on the thy gene that encodes thymidylate synthase. The system comprises a plasmid vector from Lactococcus lactis and a Thy- spontaneous mutant of R. meliloti. The plasmid is free-replicating and has a broad range of hosts.

Symbiosis, Plasmids, Genetic regulation, Genetic vectors, Rhizobium meliloti

Construction of a rhizosphere pseudomonad with potential to degrade polychlorinated biphenyls and detection of bph gene expression in the rhizosphere

Article Abstract:

The bhp gene present in bacteria which degrade polychlorinated biphenyls (PCB) was introduced into a non-essential region of Pseudomonas chromosome. The growth of the pseudomonas strain was not affected and the bacterial cells could use biphenyls for their carbon requirements. Under laboratory conditions the PCB degrading ability was unaffected and cultures of the Pseudomonas did not contain any cells which had lost this ability. Pseudomonads are found in the roots of plants and the genetically altered strains can be used for bioremediation of contaminated soil.

Microbial genetic engineering

Evidence for signalling between the phytopathogenic fungus Pythium ultimum and Pseudomonas fluorescens F113: P. ultimum represses the expression of genes in P. fluorescens F113, resulting in altered ecological fitness

Article Abstract:

The expression of Pseudomonas fluorescens F113 genes in the presence and absence of the phytopathogenic fungus Pythium ultimum was monitored to determine the ability of the fungus to alter genetic expression in Pseudomonas. Results indicate a repression of several gene clusters in P. fluorescens F113 resulting in a reduction of ecological fitness in this strain of bacteria.

Environmental aspects, Gene expression