摘要：

Pseudomonas pseudoalcaligenes AVO110 was selected as an efficient avocado root tipcolonizer, displaying antagonism towards Rosellinia necatrix, the causal agent of avocado whiteroot rot. The most likely biocontrol mechanisms used by this strain is competition for niches andnutrients. In fact, AVO110 is able to colonise competitively the surface of fungal hyphae, usingfungal exudates. In a previous study, we used signature-tagged mutagenesis (STM) to screen alibrary of AVO110 transposon mutants for their ability to grow in Rosellinia exudates (BM-REmedium). A pool of 26 growth-attenuated mutants (GAM) was identified.In this work, we used the recently obtained draft genome sequence of AVO110 to analyse thegenetic context of the genes affected by the transposon in seven GAM mutants. Among thetraits affected, we have identified homologs of an exodeoxyribonuclease, a GGDEF/EAL/PASprotein, a transcriptional regulator, a histidine kinase, a putative enterotoxin, a peptidase and aputative small RNA. Phenotypic characteristics such as biofilm formation, persistence andcolonisation of avocado roots and colonisation of fungal hyphae were studied. Mutants affectedin the transcriptional regulator and the GGDEF/EAL/PAS proteins were altered in all featuresanalysed when compared to the wild type strain. The remaining mutants presented variations inpersistence and colonisation of fungal and root surfaces, except for that affected in a putativeenterotoxin, which was only altered in fungal colonisation.Finally, quantitative RT-PCR experiments were performed in BM-RE to evaluate the expressiondynamics of these genes in the presence of the fungal metabolites along the time. Resultsshowed no evident correlation between gene expression and phenotypic behaviour.

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