| Popis: |
Xylella fastidiosa (Xf) is classified as a mesophilic bacterium particularly well adapted to areas with mild winters. The effects of temperature on Xf development have been addressed only for Xf subsp. fastidiosa strains. In this work, we have explored the effects of temperature on growth and biofilm formation in vitro for Xf strains representative of Xf subspecies prevalent in the European outbreaks. Growth, biofilm formation and cell viability of Xf strains from subsp. fastidiosa (7 strains), multiplex (18 strains), pauca (3 strains) and sandyi (2 strains) of different geographic and host origin have been determined in microplates with PD3 medium incubated at a constant temperature range of 6–32 °C at 4 °C intervals. Growth was determined daily by optical density at 600 nm, and biofilm was assessed at the end of the experiments by a crystal violet assay. Both parameters were modelled using a beta function to estimate the cardinal and optimal temperature values for each strain. Our results indicate that both growth and biofilm formation is determined by temperature and Xf strain. Overall, minimum vales for both parameters were observed at the extreme temperatures of 6 and 32 °C. However, the range with optimal values largely depends on the Xf strain. Although no distinct range was associated with subspecies, the widest temperature range for optimal growth was estimated for Xf subsp. multiplex strains at 20–32 °C. Optimal growth was estimated at 24–32 °C for Xf subsp. fastidiosa strains. No clear pattern was found for Xf subsp. pauca, with optimal values between 16 and 24 °C or 20 and 28 °C, depending on the strains. Similarly, for Xf subsp. sandyi, optimal growth occurred at 16–28 °C or 20–28 °C. With a few exceptions, similar response to temperature was observed for biofilm formation.These results would allow the development of region-specific epidemiological models to predict the risk associated with the establishment and spread of Xf strains in Europe. |
