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Natural Competence of Xylella fastidiosa Occurs at a High Frequency Inside Microfluidic Chambers Mimicking the Bacterium's Natural Habitats.

ABSTRACT: Xylella fastidiosa is a xylem-limited bacterium that is the causal agent of emerging diseases in a number of economically important crops. Genetic diversity studies have demonstrated homologous recombination occurring among X. fastidiosa strains, which has been proposed to contribute to host plant shifts. Moreover, experimental evidence confirmed that X. fastidiosa is naturally competent for recombination in vitro Here, as an approximation of natural habitats (plant xylem vessels and insect mouthparts), recombination was studied in microfluidic chambers (MCs) filled with media amended with grapevine xylem sap. First, different media were screened for recombination in solid agar plates using a pair of X. fastidiosa strains that were previously reported to recombine in coculture. The highest frequency of recombination was obtained with PD3 medium, compared to those with the other two media (X. fastidiosa medium [XFM] and periwinkle wilt [PW] medium) used in previous studies. Dissection of the media components led to the identification of bovine serum albumin as an inhibitor of recombination that was correlated to its previously known effect on inhibition of twitching motility. When recombination was performed in liquid culture, the frequencies were significantly higher under flow conditions (MCs) than under batch conditions (test tubes). The recombination frequencies in MCs and agar plates were not significantly different from each other. Grapevine xylem sap from both susceptible and tolerant varieties allowed high recombination frequency in MCs when mixed with PD3. These results suggest that X. fastidiosa has the ability to be naturally competent in the natural growth environment of liquid flow, and this phenomenon could have implications in X. fastidiosa environmental adaptation.Xylella fastidiosa is a plant pathogen that lives inside xylem vessels (where water and nutrients are transported inside the plant) and the mouthparts of insect vectors. This bacterium causes emerging diseases in various crops worldwide, including recent outbreaks in Europe. The mechanisms by which this bacterium adapts to new hosts is not understood, but it was previously shown that it is naturally competent, meaning that it can take up DNA from the environment and incorporate it into its genome (recombination). In this study, we show that the frequency of recombination is highest when the bacterium is grown under flow conditions in microfluidic chambers modeled after its natural habitats, and recombination was still high when the medium was amended with grapevine sap. Our results suggest that this bacterium is able to recombine when growing inside plants or insects, and this can be a mechanism of adaptation of this pathogen that causes incurable diseases.

SUBMITTER: Kandel PP

PROVIDER: S-EPMC4988197 | biostudies-literature | 2016 Sep

REPOSITORIES: biostudies-literature

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Natural Competence of Xylella fastidiosa Occurs at a High Frequency Inside Microfluidic Chambers Mimicking the Bacterium's Natural Habitats.

Kandel Prem P PP Lopez Samantha M SM Almeida Rodrigo P P RP De La Fuente Leonardo L

Applied and environmental microbiology 20160815 17

<h4>Unlabelled</h4>Xylella fastidiosa is a xylem-limited bacterium that is the causal agent of emerging diseases in a number of economically important crops. Genetic diversity studies have demonstrated homologous recombination occurring among X. fastidiosa strains, which has been proposed to contribute to host plant shifts. Moreover, experimental evidence confirmed that X. fastidiosa is naturally competent for recombination in vitro Here, as an approximation of natural habitats (plant xylem vess ...[more]

PMID: 27316962

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Project description:Xylella fastidiosa is an economically important bacterial plant pathogen. With insights gained from 72 genomes, this study investigated differences among the three main subspecies, which have allopatric origins: X. fastidiosa subsp. fastidiosa, multiplex, and pauca The origin of recombinogenic X. fastidiosa subsp. morus and sandyi was also assessed. The evolutionary rate of the 622 genes of the species core genome was estimated at the scale of an X. fastidiosa subsp. pauca subclade (7.62 × 10-7 substitutions per site per year), which was subsequently used to estimate divergence time for the subspecies and introduction events. The study characterized genes present in the accessory genome of each of the three subspecies and investigated the core genome to detect genes potentially under positive selection. Recombination is recognized to be the major driver of diversity in X. fastidiosa, potentially facilitating shifts to novel plant hosts. The relative effect of recombination in comparison to point mutation was calculated (r/m = 2.259). Evidence of recombination was uncovered in the core genome alignment; X. fastidiosa subsp. fastidiosa in the United States was less prone to recombination, with an average of 3.22 of the 622 core genes identified as recombining regions, whereas a specific clade of X. fastidiosa subsp. multiplex was found to have on average 9.60 recombining genes, 93.2% of which originated from X. fastidiosa subsp. fastidiosa Interestingly, for X. fastidiosa subsp. morus, which was initially thought to be the outcome of genome-wide recombination between X. fastidiosa subsp. fastidiosa and X. fastidiosa subsp. multiplex, intersubspecies homologous recombination levels reached 15.30% in the core genome. Finally, there is evidence of X. fastidiosa subsp. pauca strains from citrus containing genetic elements acquired from strains infecting coffee plants as well as genetic elements from both X. fastidiosa subsp. fastidiosa and X. fastidiosa subsp. multiplex In summary, our data provide new insights into the evolution and epidemiology of this plant pathogen.IMPORTANCEXylella fastidiosa is an important vector-borne plant pathogen. We used a set of 72 genomes that constitutes the largest assembled data set for this bacterial species so far to investigate genetic relationships and the impact of recombination on phylogenetic clades and to compare genome content at the subspecies level, and we used a molecular dating approach to infer the evolutionary rate of X. fastidiosa The results demonstrate that recombination is important in shaping the genomes of X. fastidiosa and that each of the main subspecies is under different selective pressures. We hope insights from this study will improve our understanding of X. fastidiosa evolution and biology.

Dataset Information

Natural Competence of Xylella fastidiosa Occurs at a High Frequency Inside Microfluidic Chambers Mimicking the Bacterium's Natural Habitats.

Publications

Natural Competence of Xylella fastidiosa Occurs at a High Frequency Inside Microfluidic Chambers Mimicking the Bacterium's Natural Habitats.

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