Kandel Prem P, Lopez Samantha M, Almeida Rodrigo P P, De La Fuente Leonardo
Department of Entomology and Plant Pathology, Auburn University, Auburn, Alabama, USA.
Department of Environmental Science, Policy and Management, University of California, Berkeley, California, USA.
Appl Environ Microbiol. 2016 Aug 15;82(17):5269-77. doi: 10.1128/AEM.01412-16. Print 2016 Sep 1.
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.
木质部难养菌是一种局限于木质部的细菌，是多种经济作物中一些新出现疾病的病原体。遗传多样性研究表明，木质部难养菌菌株之间会发生同源重组，有人认为这有助于宿主植物的转移。此外，实验证据证实，木质部难养菌在体外具有自然重组能力。在此，作为自然栖息地（植物木质部导管和昆虫口器）的近似环境，在充满添加了葡萄木质部汁液的培养基的微流控腔室（MCs）中研究了重组情况。首先，使用先前报道在共培养中会发生重组的一对木质部难养菌菌株，在固体琼脂平板上筛选不同的培养基用于重组。与先前研究中使用的其他两种培养基（木质部难养菌培养基[XFM]和长春花枯萎病[PW]培养基）相比，使用PD3培养基获得了最高的重组频率。对培养基成分进行剖析后发现，牛血清白蛋白是重组的抑制剂，这与其先前已知的对抑制颤动运动的作用相关。当在液体培养中进行重组时，流动条件下（微流控腔室）的频率显著高于分批培养条件下（试管）。微流控腔室和琼脂平板中的重组频率彼此无显著差异。来自易感和耐受品种的葡萄木质部汁液与PD3混合时，在微流控腔室中允许高重组频率。这些结果表明，木质部难养菌在液体流动的自然生长环境中具有自然重组能力，这种现象可能对木质部难养菌的环境适应性有影响。
木质部难养菌是一种植物病原体，生活在木质部导管（植物内部运输水和养分的地方）和昆虫传播媒介的口器中。这种细菌在全球各种作物中引发新出现的疾病，包括近期在欧洲的疫情爆发。这种细菌适应新宿主的机制尚不清楚，但先前已表明它具有自然转化能力，这意味着它可以从环境中摄取DNA并将其整合到基因组中（重组）。在本研究中，我们表明，当细菌在模拟其自然栖息地的微流控腔室中在流动条件下生长时，重组频率最高，并且当培养基用葡萄汁液改良时，重组频率仍然很高。我们的结果表明，这种细菌在植物或昆虫体内生长时能够进行重组，这可能是这种导致无法治愈疾病的病原体的一种适应机制。
