Mutants of Azospirillum brasilense Sp Cd, resistant to 5-fluorotryptophan (FT) excreted 3-indoleacetic acid (IAA), i.e., auxin, producing up to 16 μg/mL which was 30 times greater than the wild-type level. Under conditions of nitrogen fixation, the mutants excreted IAA up to 1 μg/mL, 10 times more than the wild type. However, none of the FT-resistant mutants of Azospirillum lipoferum Sp RG 20a excreted high levels of IAA. This was probably due to differences in the tryptophan and IAA biosynthetic steps between A. brasilense and A. lipoferum strains. Some of the FT-resistant mutants of A. brasilense Sp Cd showed a reduced feedback inhibition of anthranilate synthetase by tryptophan. The increased synthesis of tryptophan could explain the observed excretion of tryptophan and related metabolites. In addition, the IAA-overproducing mutants excreted other amino acids, probably owing to pleiotropic effects of deregulated tryptophan biosynthesis on amino acid metabolism. The growth patterns of some mutants excreting large amounts of IAA were almost identical to those of the wild type.

Specific Tn5 sequences inserted in the genome of Enterobacter agglomerans were detected in EcoRI digested DNA directly recovered from soil 70 d after its inoculation with the bacteria, when these were no longer culturable on agar medium. A new method of DNA extraction from soil was used. No amplification of DNA sequences by PCR was needed.

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Seven genomic libraries of chromosomal Escherichia coli K12 wild-type DNA were constructed in plasmid vectors. These were used to transform chl insertion mutants. Selection for growth on nitrate under anaerobic conditions yielded four plasmids which complemented mutants of the chlA, B, E and G types. The chromosomal fragments were mapped with restriction enzymes and subcloned. Three complementation groups were observed among the chlA mutants and two among the chlE mutants. The established complementation groups plus mutants of the chlD type represent eight distinct functions, which are all believed to be required for the molybdenum cofactor activity in the reduction of nitrate to nitrite by E. coli.

Recombinant transposon label, in vitro; Adverse soil effect; Ecological factors 1. SUMMARY In strains of nitrogen-fixing Enterobacter agglomerans, isolated from the rhizosphere of cereals, the nif genes are located on large plasmids. Plasmid pEA9 (200 kb) is self-transmissible between closely related strains. To collect data on possible uncontrolled gene spread, for planned releases of such bacteria, plasmid pEA9 was labelled with transposons (Tn1725 and Tn5) and used in mating experiments between homologous Enterobacter strains with soil as substrate. The soil was from a plot into which an actual release was being planned. In the majority of experiments it was not sterilized.Survival and plasmid transfer is described, as are variations in temperature, time, moisture, pH and soil packing. Further experiments were with or without added energy sources, and with or without plant roots. Under standard conditions Correspondence to." W. Klingmiiller,