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首页> 外文期刊>Journal of bacteriology >The Sinorhizobium meliloti Lon Protease Is Involved in Regulating Exopolysaccharide Synthesis and Is Required for Nodulation of Alfalfa
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The Sinorhizobium meliloti Lon Protease Is Involved in Regulating Exopolysaccharide Synthesis and Is Required for Nodulation of Alfalfa

机译：苜蓿中华根瘤菌（Sinorhizobium meliloti）Lon蛋白酶参与调节胞外多糖的合成，并且它是苜蓿结瘤所必需的

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While screening for Sinorhizobium meliloti Pho regulatory mutants, a transposon mutant was isolated that constitutively expressed higher levels of acid and alkaline phosphatase enzymes. This mutant was also found to form pseudonodules on alfalfa that were delayed in appearance relative to those formed by the wild-type strain, it contained few bacteroids, and it did not fix nitrogen. Sequence analysis of the transposon insertion site revealed the affected gene to have high homology to Lon proteases from a number of organisms. In minimal succinate medium, the mutant strain was found to grow more slowly, reach lower maximal optical density, and produce more extracellular polysaccharide (EPS) than the wild-type strain. The mutant fluoresced brightly on minimal succinate agar containing calcofluor (which binds to EPSI, a constitutively expressed succinoglycan), and gas chromotographic analysis of purified total EPS showed that the glucose-to-galactose ratio in the lonmutant total EPS was 5.0 ± 0.2 (mean ± standard error), whereas the glucose-to-galactose ratio in the wild-type strain was 7.1 ± 0.5. These data suggested that in addition to EPSI, thelon mutant also constitutively synthesized EPSII, a galactoglucan which is the second major EPS known to be produced byS. meliloti, but typically is expressed only under conditions of phosphate limitation. 13C nuclear magnetic resonance analysis showed no major differences between EPS purified from the mutant and wild-type strains. Normal growth, EPS production, and the symbiotic phenotype were restored in the mutant strain when the wild-type lon gene was present intrans. The results of this study suggest that the S. meliloti Lon protease is important for controlling turnover of a constitutively expressed protein(s) that, when unregulated, disrupts normal nodule formation and normal growth.
机译：当筛选 Pho调节突变体时，分离出一个转座子突变体，其组成型表达较高水平的酸和碱性磷酸酶。还发现该突变体在紫花苜蓿上形成假结节，其外观相对于野生型菌株形成的假结节有所延迟，它含有少量的类细菌，并且不固定氮。转座子插入位点的序列分析表明，受影响的基因与许多生物的Lon蛋白酶具有高度同源性。在最小的琥珀酸培养基中，发现该突变菌株比野生型菌株生长更慢，达到最低的最大光密度并产生更多的细胞外多糖（EPS）。该突变体在含有钙氟的最小琥珀酸琼脂（与EPSI，组成型表达的琥珀聚糖结合）上发出明亮的荧光，气相色谱分析纯化的总EPS显示， lon 突变体中的葡萄糖与半乳糖之比总EPS为5.0±0.2（平均值±标准误差），而野生型菌株中的葡萄糖与半乳糖之比为7.1±0.5。这些数据表明，除了EPSI之外， lon 突变体还组成性合成EPSII，一种半乳糖葡聚糖，这是已知由 S产生的第二种主要EPS。 meliloti ，但通常仅在磷酸盐限制条件下表达。 13 C核磁共振分析表明，从突变菌株和野生型菌株中纯化得到的EPS之间没有重大差异。当野生型 lon 基因存在于 trans 中时，突变株恢复了正常生长，EPS产生和共生表型。这项研究的结果表明 S。 mellonti Lon蛋白酶对于控制组成型表达蛋白的周转非常重要，这种蛋白在不受调节时会破坏正常的结节形成和正常的生长。

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