BIOCHEMICAL AND GENETIC GROUPING OF ISOLEUCINE-VALINE MUTANTS OF PSEUDOMONAS AERUGINOSA

Auxotrophic variants of Pseudomonas aeruginosa are selected from prototrophic wild-type strains in respiratory infections in patients with cystic fibrosis

Twenty-four nutritionally dependent (auxotrophic) Pseudomonas aeruginosa strains were isolated from 20 cystic fibrosis (CF) patients and tested for their amino acid requirements. Two different methods were necessary to identify the nutritional status of all isolates. Methionine was the most common single amino acid required (9 of 24 isolates), followed by leucine and arginine or ornithine. In total, a requirement for 12 different compounds or combination of compounds was demonstrated. Auxotrophic and prototrophic pairs of isolates from the same patient were compared by macrorestriction analysis of DNA in pulsed-field gel electrophoresis. Thirteen of 18 pairs analyzed presented identical restriction fragment length polymorphism profiles following digestion of DNA with XbaI. Three of the remaining pairs showed percentage similarities of 77, 91, and 98%, and the profiles of two pairs could not be compared because of the excessive degradation of their DNA. These results suggest that auxotrophic and prototrophic P. aeruginosa isolates colonizing the same CF patient constitute an isogenic group and raise the possibility that auxotrophs are selected from the prototrophic population during the course of pulmonary infection in CF patients.

Exonuclease activity from Pseudomonas aeruginosa which is missing in phenotypically restrictionless mutants

A phenotypically restrictionless strain of Pseudomonas aeruginosa was found to lack a deoxyribonuclease specific for linear duplex DNA. The purified enzyme had an optimum pH of 8.5, required MgCl2 (10 mM) for maximum activity, and did not require ATP. Neither the degradation of heat-denatured DNA nor the degradation of bacteriophage F116 DNA was detected. The genome of bacteriophage F116 was shown to possess single-stranded terminal regions, which account for the resistance to degradation and for the ability of the phage to transfect restriction-proficient strains.

The order of replication of chromosomal markers in Pseudomonas aeruginosa strain 1. I. Marker frequency analysis by transduction

The generalized transducing phage F116 has been used to prepare lysates from fast- and slow-growing cultures ofPseudomonas aeruginosastrain 1. These lysates have been used to transduce a number of auxotrophic markers to prototrophy and the ratios of the numbers of transductants obtained with each lysate have been determined. Since the markers are those which have been mapped by conjugation in previous studies it has been possible to compare the ratios obtained for each marker with the relative position of the marker on the chromosome map. If the assumption is made that there is only one circular chromosome inP. aeruginosastrain 1 it is possible to suggest a way in which two apparently unlinked segments might be joined together. It is also possible to suggest that the chromosome replicates sequentially in two directions from a fixed origin.

Control of pyrimidine biosynthesis in Pseudomonas aeruginosa

The pathway of pyrimidine biosynthesis in Pseudomonas aeruginosa has been shown to be the same as in other bacteria. Twenty-seven mutants requiring uracil for growth were isolated and the mutant lesions were identified. Mutants lacking either dihydroorotic acid dehydrogenase, orotidine monophosphate pyrophosphorylase, orotidine monophosphate decarboxylase, or aspartic transcarbamylase were isolated; none lacking dihydroorotase were found. By using transduction and conjugation, four genes affecting pyrimidine biosynthetic enzymes have been identified and shown to be unlinked to each other. The linkage of pyrB to met-28 and ilv-2 was shown by contransduction. Repression by uracil alone or by broth could not be demonstrated for any enzymes of this pathway, in contrast to the situation in Escherichia coli and Serratia marcescens. In addition, derepression of these enzymes could not be demonstrated. A low level of feedback inhibition of aspartic transcarbamylase was found to occur. It is suggested that the control of such constitutive biosynthetic enzymes in P. aeruginosa may be related to the comprehensive metabolic activities of this organism.

Genetic control of the beta-ketoadipate pathway in Pseudomonas aeruginosa

The regulation and genetic control of the beta-ketoadipate pathway in Pseudomonas aeruginosa were investigated. The pattern of enzyme induction is apparently the same as in P. putida. Mutants were obtained for all but 1 of the 11 structural genes; the proximity of these genes on the chromosome was examined by transduction of the mutants with phage F116. If a group of enzymes was induced by the same compounds, the corresponding genes were closely clustered. Surprisingly, some locispecifying enzymes not sharing a common inducer were also clustered. It is suggested that this latter finding may indicate a degree of chromosomal specialization.

Biochemical and genetic analysis of isoleucine and valine biosynthesis in Staphylococcus aureus

After a prototrophic strain of Staphylococcus aureus had been exposed to diethyl sulfate, 28 isoleucine- and isoleucine-valine-dependent mutants (ilv mutants) were isolated. On the basis of auxanography, their ability to accumulate intermediates of isoleucine and valine biosynthesis, and intergeneric syntrophism with ilv mutants of Salmonella typhimurium, all mutants were placed into four groups, each of which corresponded to a presumed enzymatic deficiency, as follows: group A, deficient in l-threonine deaminase; group B, deficient in the condensing enzyme; group C, deficient in reductoisomerase; group D, deficient in alpha-beta-dihydroxy acid dehydrase. No mutants blocked in the terminal (transaminase) reactions were isolated. Transduction analyses (best-fit, ratio, and complementation tests) with the use of phage 83 established that the linear arrangement of the structural genes is identical with the order of participation of their enzymes in isoleucine and valine biosynthesis, and that these genes comprise a single linkage group which can exist on a single donor fragment during transduction.