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The present study compares the pathogenicity on olive and oleander plants of three wild‐type strains of Pseudomonas syringae subsp. savastanoi (ITM317 and PBa230 from olive and ITM519 from oleander) and three phytohormone‐deficient mutants of ITM519: ITM519‐41 (Iaa+/cytokinins‐), ITM519‐7 (Iaa−/cytokinins+), ITM519‐6 (Iaa−/cytokinins−), Mutants not producing IAA (ITM519‐7and ITM519‐6) only induced necrosis of the inoculated tissues (ITM519‐,6) or swellings on the stems attributed to cytokinin production accompanied by necrosis (ITM519‐7). By contrast, the Iaa+/cytokinins− mutant (ITM519‐41) induced attenuated symptoms on stems and knots similar to those obtained with the parent strain on oleander leaves. Olive strains induced necrosis of oleander leaves and were virulent and avirulent, respectively, on olive and oleander stems. Strain ITM519 and its three mutants were all able to multiply in oleander leaves at similar rates, reaching the same final populations. By contrast, the two olive strains multiply poorly, reaching populations c.102‐fold lower. These results confirm that expression of IAA genes alone is sufficient to initiate the development of knots on oleander while cytokinins are necessary for the full expression of the disease symptoms (determining knot size). The findings also indicate that the plant tissues (stems and leaves) react differently to the various strains of the bacterium and, furthermore, suggest that, besides phytohormones, other pathogenetic factors could be involved in this host‐pathogen interaction. The necrotic reaction of oleander leaves heavily inoculated with olive strains was interpreted as a possible form of hypersensitivity reaction.

The virulence of Pseudomonas syringae subsp. savastanoi, which causes hyperplastic symptoms (knots) on olive plants, is associated with secreted phytohormones. We identified a Tn5-induced mutant of P. syringae subsp. savastanoi that did not cause disease symptoms on olive plants although it was still able to produce phytohormones. In addition, the mutant failed to elicit a hypersensitive response in a nonhost plant. Molecular characterization of the mutant revealed that a single Tn5 insertion occurred within an open reading frame encoding a protein 92% identical to the HrcC protein of P. syringae pv. syringae. Moreover, sequence analysis revealed that the gene encoding the HrcC protein in P. syringae subsp. savastanoi was part of an operon that included five genes arranged as in other phytopathogenic bacteria. These results imply that hrp/hrc genes are functional in P. syringae subsp. savastanoi and that they play a key role in the pathogenicity of this plant pathogen.

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Results of a survey of olive knot disease in central Italy in 2002 and 2003 showed that Pantoea agglomerans was found associated with the pathogen Pseudomonas savastanoi pv. savastanoi ( Ps. savastanoi ) in 70% of the olive knots examined. Pathogenicity tests in which these two bacteria were co-inoculated on the stems of 1-year-old olive plants at ratios of 1:1, 1:100 and 100:1 showed that the growth of P. agglomerans was apparently aided by the presence of an actively growing population of Ps. savastanoi . At the same time, however, a dominant population of P. agglomerans at the inoculation site tended to depress the growth of Ps. savastanoi , probably because of competition for space and nutrients between these bacteria and by means of antibiotic production by P. agglomerans. In some cases the association of P. agglomerans , which in culture was found to produce indole-3-acetic acid but not cytokinins, with Ps. savastanoi resulted in an increase in the size of knots. This boosting effect of P. agglomerans on proliferation was probably due to the release of IAA by this bacterium at the inoculation sites.

Ochratoxin A (OTA) is a mycotoxin with a main nephrotoxic activity contaminating several foodstuffs. In the present report, five soil samples collected from OTA-contaminated vineyards were screened to isolate microorganisms able to biodegrade OTA. When cultivated in OTA-supplemented medium, OTA was converted in OTα by 225 bacterial isolates. To reveal clonal relationships between isolates, molecular typing by using an automated rep-PCR system was carried out, thus showing the presence of 27 different strains (rep-PCR profiles). The 16S-rRNA gene sequence analysis of an isolate representative of each rep-PCR profiles indicated that they belonged to five bacterial genera, namely Pseudomonas, Leclercia, Pantoea, Enterobacter, and Acinetobacter. However, further evaluation of OTA-degrading activity by the 27 strains revealed that only Acinetobacter calcoaceticus strain 396.1 and Acinetobacter sp. strain neg1, consistently conserved the above property; their further characterization showed that they were able to convert 82% and 91% OTA into OTα in six days at 24 °C, respectively. The presence of OTα, as the unique OTA-degradation product was confirmed by LC-HRMS. This is the first report on OTA biodegradation by bacterial strains isolated from agricultural soils and carried out under aerobic conditions and moderate temperatures. These microorganisms might be used to detoxify OTA-contaminated feed and could be a new source of gene(s) for the development of a novel enzymatic detoxification system.