Xylella fastidiosa subsp. pauca and olive produced lipids moderate the switch adhesive versus non-adhesive state and viceversa

Abstract

Global trade and climate change are re-shaping the distribution map of pandemic pathogens. One major emerging concern is Xylella fastidiosa, a tropical bacterium recently introduced into Europe from America. In last decades, X. fastidiosa was detected in several European countries. X. fastidiosa is an insect vector-transmitted bacterial plant pathogen associated with severe diseases in a wide range of hosts. X. fastidiosa through a tight coordination of the adherent biofilm and the planktonic states, invades the host systemically. The planktonic phase is correlated to low cell density and vessel colonization. Increase in cell density triggers a quorum sensing system based on mixture of cis 2-enoic fatty acids-diffusible signalling factors (DSF) that promote stickiness and biofilm. The lipidome profile of Olea europaea L. (cv. Ogliarola salentina) samples, collected in groves located in infected zones and uninfected zones was performed. The untargeted analysis of the lipid profiles of Olive Quick Decline Syndrome (OQDS) positive (+) and negative (-) plants showed a clustering of OQDS+ plants apart from OQDS-. The targeted lipids profile of plants OQDS+ and OQDS- identified a shortlist of 10 lipids that increase their amount in OQDS+ and X. fastidiosa positive olive trees. These lipid entities, provided to X. fastidiosa subsp. pauca pure culture, impact on the dual phase, e.g. planktonic ↔ biofilm. This study provides novel insights on OQDS lipid hallmarks and on molecules that might modulate biofilm phase in X. fastidiosa subsp. pauca.

Fig 1. Volcano plot analysis of 437 compounds on negative ion scan, in Xf+ and Xf- samples.

The x-axis shows the fold change to indicate the variation in abundance of compounds present in Xf+ compared to Xf- samples. The compounds on the right side were more abundant, whereas those on the left side were less abundant in Xf+ condition. Entities that satisfied the fold change and the P-value cut-off of 2.0 and 0.05, respectively, are marked in red.

Fig 2. Principal component analysis.

Score plot of data generated by HPLC-ESI/TOF-MS analysis of Xf+ (red square) and Xf- (blue square) samples. The results of the analysis referred to three separate experiments performed in triplicates.

Fig 3. Boxplots of statistically significant compounds analyzed by MRM or SIM.

Comparisons between naturally non-infected (Xf negative) and naturally infected (Xf positive) plant samples are displayed on X-axis. The Y-axis shows the normalized relative abundance. Horizontal line in each boxplot indicates the median and black dots represent the outlier samples.

Fig 4

Boxplots of effects caused by lipid compounds on planktonic growth (A) and biofilm formation (B). Selected compounds (FFA, DAG and oxylipins) are the ones with the most relevant effect, measured as OD fold-change, considering 0.0025mg mL^-1 concentration versus control. The Y-axis displays the optical density (OD). The X-axis displays the compounds (Statistical significance assessed trough Kruskal Wallis test, p-value <0.05). Horizontal line in each boxplot indicates the median and black dots represent the outlier samples.