García-de los Santos Alejandro, Morales Alejandro, Baldomá Laura, Clark Scott R D, Brom Susana, Yost Christopher K, Hernández-Lucas Ismael, Aguilar Juan, Hynes Michael F
Programa de Genética Molecular de Plásmidos Bacterianos, Centro de Investigación sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México (UNAM), Apdo. Postal 565-A, Cuernavaca, Mor. México.
Can J Microbiol. 2002 Oct;48(10):922-32. doi: 10.1139/w02-091.
In the course of a study conducted to isolate genes upregulated by plant cell wall sugars, we identified an arabinose-inducible locus from a transcriptional fusion library of Rhizobium leguminosarum VF39, carrying random insertions of the lacZ transposon Tn5B22. Sequence analysis of the locus disrupted by the transposon revealed a high similarity to uncharacterized malate synthase G genes from Sinorhizobium meliloti, Agrobacterium tumefaciens, and Mesorhizobium loti. This enzyme catalyzes the condensation of glyoxylate and acetyl-CoA to yield malate and CoA and is thought to be a component of the glyoxylate cycle, which allows microorganisms to grow on two carbon compounds. Enzyme assays showed that a functional malate synthase is encoded in the glcB gene of R. leguminosarum and that its expression is induced by arabinose, glycolate, and glyoxylate. An Escherichia coli aceB glcB mutant, complemented with the R. leguminosarum PCR-amplified gene, recovered malate synthase activity. A very similar genome organization of the loci containing malate synthase and flanking genes was observed in R. leguminosarum, S. meliloti, and A. tumefaciens. Pea plants inoculated with the glcB mutant or the wild-type strain showed no significant differences in nitrogen fixation. This is the first report regarding the characterization of a mutant in one of the glyoxylate cycle enzymes in the rhizobia.
在一项旨在分离受植物细胞壁糖类上调的基因的研究过程中，我们从携带lacZ转座子Tn5B22随机插入的豌豆根瘤菌VF39转录融合文库中鉴定出一个阿拉伯糖诱导型基因座。对被转座子破坏的基因座进行序列分析，发现其与来自苜蓿中华根瘤菌、根癌农杆菌和百脉根中慢生根瘤菌的未表征苹果酸合酶G基因高度相似。该酶催化乙醛酸和乙酰辅酶A缩合生成苹果酸和辅酶A，被认为是乙醛酸循环的一个组成部分，乙醛酸循环使微生物能够利用二碳化合物生长。酶活性测定表明，豌豆根瘤菌的glcB基因编码一种功能性苹果酸合酶，其表达受阿拉伯糖、乙醇酸和乙醛酸诱导。用豌豆根瘤菌PCR扩增基因互补的大肠杆菌aceB glcB突变体恢复了苹果酸合酶活性。在豌豆根瘤菌、苜蓿中华根瘤菌和根癌农杆菌中观察到含有苹果酸合酶和侧翼基因的基因座具有非常相似的基因组结构。接种glcB突变体或野生型菌株的豌豆植株在固氮方面没有显著差异。这是关于根瘤菌中乙醛酸循环酶之一的突变体表征的首次报道。
