Laboratório de Microbiologia do Solo, ICAAM (Instituto de Ciências Agrárias e Ambientais Mediterrânicas), Universidade de Évora, Apartado 94, 7002-554, Évora, Portugal.
Microb Ecol. 2013 Jan;65(1):145-53. doi: 10.1007/s00248-012-0098-7. Epub 2012 Aug 14.
Our goals were to evaluate the tolerance of mesorhizobia to acid and alkaline conditions as well as to investigate whether acid tolerance is related to the species or the origin site of the isolates. In addition, to investigate the molecular basis of acid tolerance, the expression of chaperone genes groEL and dnaKJ was analyzed using acid-tolerant and sensitive mesorhizobia. Tolerance to pH 5 and 9 was evaluated in liquid medium for 98 Portuguese chickpea mesorhizobia belonging to four species clusters. All isolates showed high sensitivity to pH 9. In contrast, mesorhizobia revealed high diversity in terms of tolerance to acid stress: 35 % of the isolates were acid sensitive and 45 % were highly tolerant to pH 5 or moderately acidophilic. An association between mesorhizobia tolerance to acid conditions and the origin soil pH was found. Furthermore, significant differences between species clusters regarding tolerance to acidity were obtained. Ten isolates were used to investigate the expression levels of the chaperone genes by northern hybridization. Interestingly, most acid-tolerant isolates displayed induction of the dnaK and groESL genes upon acid shock while the sensitive ones showed repression. This study suggests that acid tolerance in mesorhizobia is related to the pH of the origin soil and to the species cluster of the isolates. Additionally, the transcriptional analysis suggests a relationship between induction of major chaperone genes and higher tolerance to acid pH in mesorhizobia. This is the first report on transcriptional analysis of the major chaperones genes in mesorhizobia under acidity, contributing to a better understanding of the molecular mechanisms of rhizobia acidity tolerance.
我们的目标是评估中慢生根瘤菌对酸碱条件的耐受性，以及研究耐酸性是否与菌株的种类或来源地有关。此外，为了研究耐酸性的分子基础，我们分析了耐酸和敏感中慢生根瘤菌中伴侣蛋白基因 groEL 和 dnaKJ 的表达。在液体培养基中，用 98 株属于四个种簇的葡萄牙鹰嘴豆中慢生根瘤菌来评估它们对 pH5 和 9 的耐受性。所有分离株对 pH9 均高度敏感。相比之下，中慢生根瘤菌在耐酸应激方面表现出高度多样性：35%的分离株对酸敏感，45%的分离株对 pH5 或中度嗜酸高度耐受。发现中慢生根瘤菌对酸条件的耐受性与来源土壤 pH 值之间存在关联。此外，还获得了种簇之间关于耐酸性的显著差异。用 10 株分离株通过 northern 杂交来研究伴侣蛋白基因的表达水平。有趣的是，大多数耐酸分离株在酸冲击时显示 dnaK 和 groESL 基因的诱导，而敏感分离株则显示抑制。本研究表明，中慢生根瘤菌的耐酸性与来源土壤的 pH 值和分离株的种簇有关。此外，转录分析表明，主要伴侣蛋白基因的诱导与中慢生根瘤菌对酸 pH 值的更高耐受性之间存在关系。这是首次报道在酸度下对中慢生根瘤菌主要伴侣蛋白基因进行转录分析，有助于更好地理解根瘤菌耐酸性的分子机制。
