Smit G, Kijne J W, Lugtenberg B J
J Bacteriol. 1987 Sep;169(9):4294-301. doi: 10.1128/jb.169.9.4294-4301.1987.
We have previously described an assay for the attachment of Rhizobium bacteria to pea root hair tips (cap formation) which was used as a model to study the attachment step in the nodulation process. Under all conditions tested, a positive correlation was observed between the percentage of fibrillated cells and the ability of these bacteria to form caps and to adhere to glass, suggesting that fibrils play a role in the attachment of Rhizobium leguminosarum to pea root hair tips and to glass (G. Smit, J. W. Kijne, and B. J. J. Lugtenberg, J. Bacteriol. 168:821-827, 1986). In the present paper the chemical and functional characterization of the fibrils of R. leguminosarum is described. Characterization of purified fibrils by infrared spectroscopy and cellulase treatment followed by thin-layer chromatography showed that the fibrils are composed of cellulose. Purified cellulose fibrils, as well as commercial cellulose, inhibited cap formation when present during the attachment assay. Incubation of the bacteria with purified cellulase just before the attachment assay strongly inhibited cap formation, indicating that the fibrils are directly involved in the attachment process. Tn5-induced fibril-overproducing mutants showed a greatly increased ability to form caps, whereas Tn5-induced fibril-negative mutants lost this ability. None of these Tn5 insertions appeared to be located on the Sym plasmid. Both types of mutants showed normal nodulation properties, indicating that cellulose fibrils are not a prerequisite for successful nodulation under the conditions used. The ability of the fibril-negative mutants to attach to glass was not affected by the mutations, indicating that attachment to pea root hair tips and attachment to glass are (partly) based on different mechanisms. However, growth of the rhizobia under low Ca2+ conditions strongly reduced attachment to glass and also prevented cap formation, although it had no negative effect on fibril synthesis. This phenomenon was found for several Rhizobium spp. It was concluded that both cellulose fibrils and a Ca2+ -dependent adhesin(s) are involved in the attachment of R. leguminosarum to pea root hair tips. A model cap formation as a two-step process is discussed.
我们之前描述了一种用于研究根瘤菌附着在豌豆根毛尖端（帽形成）的检测方法，该方法被用作研究结瘤过程中附着步骤的模型。在所有测试条件下，观察到纤维化细胞的百分比与这些细菌形成帽以及附着在玻璃上的能力之间存在正相关，这表明纤维在豌豆根瘤菌附着于豌豆根毛尖端和玻璃上发挥作用（G. 斯密特、J. W. 基涅和B. J. J. 卢滕贝格，《细菌学杂志》168:821 - 827，1986年）。在本文中，描述了豌豆根瘤菌纤维的化学和功能特性。通过红外光谱和纤维素酶处理后进行薄层色谱对纯化纤维进行表征，结果表明纤维由纤维素组成。在附着检测过程中，纯化的纤维素纤维以及商业纤维素的存在会抑制帽的形成。在附着检测前用纯化的纤维素酶孵育细菌会强烈抑制帽的形成，这表明纤维直接参与附着过程。Tn5诱导的纤维过量产生突变体形成帽的能力大大增强，而Tn5诱导的纤维阴性突变体则失去了这种能力。这些Tn5插入似乎都不在共生质粒上。这两种类型的突变体都表现出正常的结瘤特性，这表明在所用条件下，纤维素纤维不是成功结瘤的先决条件。纤维阴性突变体附着在玻璃上的能力不受突变影响，这表明附着在豌豆根毛尖端和附着在玻璃上（部分）基于不同的机制。然而，根瘤菌在低Ca2 +条件下生长会强烈降低其附着在玻璃上的能力，并且也会阻止帽的形成，尽管这对纤维合成没有负面影响。在几种根瘤菌属中都发现了这种现象。得出的结论是，纤维素纤维和一种Ca2 +依赖性粘附素都参与了豌豆根瘤菌附着在豌豆根毛尖端的过程。讨论了帽形成作为一个两步过程的模型。
