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Xylella fastidiosa 9a5c: gomesin-treated cells vs. control

ABSTRACT: In the xylem vessels of susceptible hosts, such as citrus trees or grapevines, Xylella fastidiosa forms biofilm like-colonies that can block water transport, which appears to correlate to disease symptoms. Besides helping host colonization, bacterial biofilms play an important role in resistance against antimicrobial agents, for instance antimicrobial peptides (AMP). Here we show that gomesin, a potent AMP from a Brazilian tarantula spider, modulates X. fastidiosa gene expression profile upon 60 min treatment with a sublethal concentration. Data from DNA microarray hybridizations revealed that among the up-regulated coding sequences (CDS), some are related to biofilm production. In addition, we show that the biofilm formed by gomesin-treated bacteria is thicker than that formed by non-treated cells or cells exposed to streptomycin. We have also observed that treatment of X. fastidiosa with sublethal concentration of gomesin before inoculation in tobacco plants correlates with reduction in CVC symptoms, an effect possibly due to trapping of bacterial cells to fewer xylem vessels given the enhancement in biofilm production. Together, our results suggest that X. fastidiosa can selectively sense a sublethal concentration of gomesin modulating its gene expression to produce a stronger biofilm that may protect itself against the toxic effects of this AMP.

ORGANISM(S): Xylella fastidiosa

PROVIDER: GSE17605 | GEO | 2010/01/06

SECONDARY ACCESSION(S): PRJNA118559

REPOSITORIES: GEO

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Project description:Citrus variegated chlorosis (CVC), caused by Xylella fastidiosa, is an important citrus disease that produces chlorotic injuries on leaves and reduced fruit size. This bacterium colonizes plant xylem, thereby interrupting sap flow. Other disease symptoms depend on environmental factors, since asymptomatic and symptomatic CVC plants may be genetically similar. The endophytic microbiome comprises many microbial species that may interact with pathogens, reducing disease symptoms and improving plant growth. However, the genetic and physiological mechanisms that underlie this interaction are largely unknown. In this study, the citrus endophytic bacterium Methylobacterium mesophilicum SR1.6/6 was isolated from healthy plants. This bacterium was able to colonize citrus xylem and could be transferred from plant to plant by Bucephalogonia xanthopis (Insecta), suggesting that this endophytic bacterium may interact with X. fastidiosa in planta, as a result of co-transmission by the same insect vector. To better understand how X. fastidiosa genetic responds to the presence of M. mesophilicum in the same environment, we used microarrays to evaluate the transcriptional profile of X. fastidiosa, after in vitro co-cultivation with M. mesophilicum SR1.6/6. The results showed that during co-cultivation with M. mesophilicum, X. fastidiosa downregulated genes related to growth, while genes related to energy production (cellular respiration) and transport were upregulated. Moreover, X. fastidiosa modulates genes associated with molecular recognition, nutrient competition and the stress response, suggesting the existence of a specific adaptive response to the presence of M. mesophilicum in the culture medium To evaluate and compare the Xylella fastidiosa 9a5c transcriptome profiles from bacteria cultured in PW and in co-cultive with Methylobacterium mesophilicum SR1.6/6, bacterial cultures were harvested for total RNA extraction after 24h of inoculation. Samples from the resulting RNAs were then used in competitive hybridizations against Xf microarrays. Replicated experiments were performed with RNA preparations from cells in each treatment and since each microarray carried two replicas of each spotted gene, we ended up with a series of 4 independent readings for each gene present in the microarrays. Images were analyzed with the TIGR Spotfinder program (v.2.2.4). All spots with median values lower than the median local background plus two Standard Deviations have been flagged and excluded from further analyses. Replicated experiments were performed with two independent RNA preparations from cells cultivated in each medium. For each pair of RNA preparations, two independent hybridizations were performed, with dye swaps within each pair. The results from each hybridization were submitted to a series of mathematical transformations with the aid of the software TIGR MIDAS v.2.19. These included filtering out all spots whose integrated intensities were below 10,000 a/d units, normalization between the two channels with the aid of the Lowess algorithm and SD regularization of the Cy5/Cy3 ratios across all sectors (blocks) of the array. Finally, the results from each individual experiment were loaded into the software TIGR Multi-Experiment Viewer (TMEV), v.3.01. Experiments were then normalized and genes that displayed statistically significant modulation were identified with the aid of the one-class option of the Significance Analysis of Microarrays (SAM) test, described by Tusher et al. (2001). The Î´ factor of the SAM test was adjusted to guarantee a False Discovery Rate (FDR) < 1.

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Xylella fastidiosa 9a5c: gomesin-treated cells vs. control

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