Department of Plant Pathology, Washington State University, Pullman, Washington, USA.
Appl Environ Microbiol. 2012 Feb;78(3):804-12. doi: 10.1128/AEM.06784-11. Epub 2011 Dec 2.
Natural antibiotics are thought to function in the defense, fitness, competitiveness, biocontrol activity, communication, and gene regulation of microorganisms. However, the scale and quantitative aspects of antibiotic production in natural settings are poorly understood. We addressed these fundamental questions by assessing the geographic distribution of indigenous phenazine-producing (Phz(+)) Pseudomonas spp. and the accumulation of the broad-spectrum antibiotic phenazine-1-carboxylic acid (PCA) in the rhizosphere of wheat grown in the low-precipitation zone (<350 mm) of the Columbia Plateau and in adjacent, higher-precipitation areas. Plants were collected from 61 commercial wheat fields located within an area of about 22,000 km(2). Phz(+) Pseudomonas spp. were detected in all sampled fields, with mean population sizes ranging from log 3.2 to log 7.1 g(-1) (fresh weight) of roots. Linear regression analysis demonstrated a significant inverse relationship between annual precipitation and the proportion of plants colonized by Phz(+) Pseudomonas spp. (r(2) = 0.36, P = 0.0001). PCA was detected at up to nanomolar concentrations in the rhizosphere of plants from 26 of 29 fields that were selected for antibiotic quantitation. There was a direct relationship between the amount of PCA extracted from the rhizosphere and the population density of Phz(+) pseudomonads (r(2) = 0.46, P = 0.0006). This is the first demonstration of accumulation of significant quantities of a natural antibiotic across a terrestrial ecosystem. Our results strongly suggest that natural antibiotics can transiently accumulate in the plant rhizosphere in amounts sufficient not only for inter- and intraspecies signaling but also for the direct inhibition of sensitive organisms.
天然抗生素被认为在微生物的防御、适应性、竞争力、生物防治活性、通讯和基因调控中发挥作用。然而，在自然环境中抗生素产生的规模和定量方面的了解甚少。我们通过评估在哥伦比亚高原低降水区(<350 毫米)和相邻高降水区种植的小麦根际中土著产吩嗪(PHz(+))假单胞菌的地理分布以及广谱抗生素吩嗪-1-羧酸(PCA)的积累情况，来解决这些基本问题。从位于约 22000km²的一个区域内的 61 个商业小麦田中收集了植物样本。在所采样的所有田地中都检测到 Phz(+)假单胞菌，根中平均种群大小范围从 log 3.2 到 log 7.1g(-1)(新鲜重量)。线性回归分析表明，年降水量与 Phz(+)假单胞菌定植的植物比例呈显著负相关(r²=0.36，P=0.0001)。在从 29 个选定进行抗生素定量的田地中，有 26 个田地的根际中检测到 PCA 的浓度高达纳摩尔。从根际中提取的 PCA 量与 Phz(+)假单胞菌的种群密度呈直接关系(r²=0.46，P=0.0006)。这是首次在陆地生态系统中积累大量天然抗生素的证明。我们的结果强烈表明，天然抗生素可以在植物根际中暂时积累，其数量不仅足以进行种间和种内信号传递，而且足以直接抑制敏感生物。
