Department of Genetics, CCS Haryana Agricultural University, Hisar, 125 004 Haryana India.
Indian J Microbiol. 2007 Dec;47(4):279-88. doi: 10.1007/s12088-007-0053-3. Epub 2008 Jan 11.
Among the various types of mutations studied in rhizobia, the auxotrophic mutations (which confer on the mutants the inability to synthesize certain essential substances such as amino acids, vitamins and nucleic acids), are the most favoured ones as these can be used as suitable markers for genetic analysis. An important property of rhizobia is their effectiveness i.e. their ability to fix atmospheric nitrogen into ammonia within the nodule. Special interest in this category of mutations by rhizobial geneticists is due to the fact that there is a strong correlation between the metabolic defects and the ineffectiveness (Nod(-) and/or Fix(-)) of the rhizobial strains. Auxotrophic mutants of various species of rhizobia with defects in the synthesis of nucleic bases, vitamins and amino acids have been obtained by mutagenising with physical, chemical and Tn5 mutagens. These mutants have been used in mapping studies as well as in establishing a correlation between its metabolic requirement and symbiotic relationship with the host plant. The present review deals with the isolation of auxotrophs, and their genetic, biochemical and symbiotic characterization. The review also encompasses the studies on the elucidation of biosynthetic pathways of nutritional substances in rhizobia.
在已研究的根瘤菌的各种突变类型中，营养缺陷型突变（导致突变体无法合成某些必需物质，如氨基酸、维生素和核酸）是最受欢迎的，因为它们可用作遗传分析的合适标记。根瘤菌的一个重要特性是其有效性，即在根瘤中能够将大气氮固定为氨。根瘤菌遗传学家对这类突变特别感兴趣，是因为代谢缺陷与根瘤菌菌株的无效性（Nod(-)和/或 Fix(-)）之间存在很强的相关性。通过物理、化学和 Tn5 诱变剂诱变各种根瘤菌物种，获得了在核酸碱基、维生素和氨基酸合成方面有缺陷的营养缺陷型突变体。这些突变体已被用于图谱研究以及建立其代谢需求与与宿主植物共生关系之间的相关性。本综述涉及营养缺陷型突变体的分离及其遗传、生化和共生特性。综述还包括对根瘤菌营养物质生物合成途径阐明的研究。
