Tests of Specificity of Competition Amound Pseudomonas Syringae Strains on Plants Using Recombinant Ice-Strains and Use of Ice Nucleation Genes as Probes of in Situ Transcriptional Activity. In: Hennecke H, Verma DPS, editors. Advances in Molecular Genetics of Plant-Microbe Interactions Vol. 1. Dordrecht: Springer Netherlands; 1991. pp. 457-64. [DOI: 10.1007/978-94-015-7934-6_69]

Fate of genetically modified Rhizobium leguminosarum biovar viciae during long-term storage of commercial inoculants

A study was carried out to assess the behaviour, in terms of strain survival and genetic stability, of genetically modified micro-organisms (GEMs) during their storage in commercial-type agricultural inoculants. Three genetically modified Rhizobium leguminosarum biovar viciae strains were constructed, using a gene cassette containing an inducible lacZ gene from Escherichia coli and mercury resistance determinants from transposon Tn 1831. In the first case the genes have been integrated into the chromosome, the second strain contains the inducible cassette on a plasmid, in the third case the cassette is carried by the same plasmid, but the lacZ is constitutively expressed at high levels, due to the removal of the regulatory structure (lac operator) between the gene and its promoter. Three inoculum formulations, based on liquid, vermiculite and peat carriers, were prepared using the genetically modified strains, and were monitored during a period of up to 16 months. Results indicate a high stability of the chromosomally integrated markers. The plasmid-borne modification also was very stable, though the presence of the plasmid affected the strain growth kinetics. In contrast, the strain containing the highly expressed lacZ showed dramatic marker instability. Strain behaviour in stored inoculant packages reflected that observed in batch cultures; moreover, prolonged storage appeared to magnify differences found in in vitro cultures.

Ecological Similarity and Coexistence of Epiphytic Ice-Nucleating (Ice + ) Pseudomonas syringae Strains and a Non-Ice-Nucleating (Ice - ) Biological Control Agent

De Wit replacement series were used to study competitive interactions between epiphytic Ice + Pseudomonas syringae strains and the biological frost control agents Ice - P. syringae TLP2del1 and Pseudomonas fluorescens A506. Mixtures containing two strains in different proportions but at a constant total population size were inoculated onto potato leaves. The population sizes of each strain and the total population size were determined when the community had reached equilibrium. A near-isogenic P. syringae strain pair exhibited an interaction similar to that expected for strains competing equally for limiting environmental resources. Replacement series with nonisogenic Ice + and Ice - P. syringae strain pairs suggested that these strains competed for limiting resources according to their relative competitive abilities. There was no evidence of any niche differentiation between the Ice + P. syringae strains and the Ice - P. syringae strain. The growth responses of epiphytes following addition of nutrients to the phyllosphere indicated that the epiphytic P. syringae populations were nutrient limited and that, under growth chamber conditions, the populations were more limited by the availability of carbon than by the availability of nitrogen. Determination of in vitro carbon source utilization profiles provided further evidence for the lack of niche differentiation between the Ice + and the Ice - P. syringae strains. Niche overlap indices calculated for the Ice + P. syringae strains with respect to Ice - P. syringae TLP2del1 were uniformly high, indicating ecological similarity, and were consistent with the observed low level of coexistence. The biological frost control agent P. fluorescens A506 replaced P. syringae. This was correlated with a high degree of niche overlap between these species.