O'hara Graham W, Goss Thomas J, Dilworth Michael J, Glenn Andrew R
Nitrogen Fixation Research Group, School of Biological and Environmental Sciences, Murdoch University, Murdoch 6150, Western Australia, Australia.
Appl Environ Microbiol. 1989 Aug;55(8):1870-1876. doi: 10.1128/aem.55.8.1870-1876.1989.
The development and function of the Rhizobium meliloti-Medicago sp. symbiosis are sensitive to soil acidity. Physiological criteria that can be measured in culture which serve to predict acid tolerance in soil would be valuable. The intracellular pH of R. meliloti was measured using either radioactively labeled weak acids (5,5-dimethyloxazolidine-2,4-dione and butyric acid) or pH-sensitive fluorescent compounds; both methods gave similar values. Six acid-tolerant strains (WSM419, WSM533, WSM539, WSM540, WSM852, and WSM870) maintained an alkaline intracellular pH when the external pH was between 5.6 and 7.2. In contrast, two Australian commercial inoculant strains (CC169 and U45) and four acid-sensitive strains from alkaline soils in Iraq (WSM244, WSM301, WSM365, and WSM367) maintained an alkaline intracellular pH when the external pH was >/=6.5, but had intracellular pH values of </=6.8 when the external pH was </=6.0. Four transposon Tn5-induced mutants of acid-tolerant strain WSM419, impaired in their ability to grow at pH 5.6, showed limited control over the intracellular pH. The ability to generate a large pH gradient under acid conditions may be a better indicator of acid tolerance in R. meliloti under field conditions than is growth on acidic agar plates.
苜蓿中华根瘤菌与苜蓿属植物共生关系的发育和功能对土壤酸度敏感。能够在培养物中测量的、可用于预测土壤中耐酸性的生理标准将很有价值。使用放射性标记的弱酸（5,5 - 二甲基恶唑烷 - 2,4 - 二酮和丁酸）或pH敏感荧光化合物测量了苜蓿中华根瘤菌的细胞内pH；两种方法得到的值相似。当外部pH在5.6至7.2之间时，六个耐酸菌株（WSM419、WSM533、WSM539、WSM540、WSM852和WSM870）维持碱性细胞内pH。相比之下，两个澳大利亚商业接种菌株（CC169和U45）以及来自伊拉克碱性土壤的四个酸敏感菌株（WSM244、WSM301、WSM365和WSM367）在外部pH≥6.5时维持碱性细胞内pH，但当外部pH≤6.0时，细胞内pH值≤6.8。耐酸菌株WSM419的四个转座子Tn5诱导突变体在pH 5.6下生长能力受损，对细胞内pH的控制有限。在酸性条件下产生大pH梯度的能力可能比在酸性琼脂平板上生长更能作为苜蓿中华根瘤菌在田间条件下耐酸性的指标。
