CONICET | Buscador de Institutos y Recursos Humanos

P. fluorescens Pf-5 inhabits the rhizosphere and produces several secondary metabolites that suppress the growth of soil-borne plant pathogens. Several works have demonstrated that this strain is able to efficiently colonize roots infected by Fusarium spp. and suppress diseases caused by these fungi. Species of the genus Fusarium produce important economic losses worldwide in several crops and have been extensively studied because of the mycotoxins they produce. Fusaric acid (FA), one of these mycotoxins, contributes to wilt and root diseases of various crops, is toxic to animals and humans and is a frequent contaminant of cereals grains. In P. chlororaphis and P. fluorescens FA reduces the production of antibiotics involved in the biological control of Fusarium in vivo and in vitro. In this way, FA severely affects the competition of these strains against soil-borne pathogens. Taking this into account the aim of this work was to study the effects of FA on growth and on different phenotypic traits related to colonization and biocontrol in P. fluorescens Pf-5, such as motility and production of siderophores. P. fluorescens Pf-5 showed a very high resistance to FA. The minimal inhibitory concentration, MIC, obtained for this strain was 8 mM, meanwhile for E. coli the MIC was 1.3 mM. Subinhibitory concentrations of FA reduced growth of P. fluorescens Pf-5 after the onset of the stationary phase, as well as swarming and swimming motility. No effect of FA was observed on twitching motility. Addition of FA to P. fluorescens Pf-5 cultures grown in King B medium did not affect pyoverdine production. On the other hand, the ability of P. fluorescens Pf-5 to grow in the presence of FA can be attributed to the presence of genes involved in FA detoxification and/or export. Inspection of the genome of this bacterium revealed the existence of two operons encoding proteins that show high similarity to proteins involved in FA resistance in the bacteria Burkholderia cepacia and Klebsiella oxytoca. In order to find out if these genes are involved in FA resistance in P. fluorescens Pf-5, one or both operons were eliminated. The deletion of these operons did not affect FA resistance in Pf-5, indicating that other mechanisms are involved in FA resistance in this strain.