Programa de Genómica Funcional de Procariotes, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos 62210, Mexico.
Centre of Excellence in Mass Spectrometry and Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK.
Microbiology (Reading). 2018 Apr;164(4):600-613. doi: 10.1099/mic.0.000615.
Polyamines (PAs) are ubiquitous polycations derived from basic l-amino acids whose physiological roles are still being defined. Their biosynthesis and functions in nitrogen-fixing rhizobia such as Sinorhizobium meliloti have not been extensively investigated. Thin layer chromatographic and mass spectrometric analyses showed that S. meliloti Rm8530 produces the PAs, putrescine (Put), spermidine (Spd) and homospermidine (HSpd), in their free forms and norspermidine (NSpd) in a form bound to macromolecules. The S. meliloti genome encodes two putative ornithine decarboxylases (ODC) for Put synthesis. Activity assays with the purified enzymes showed that ODC2 (SMc02983) decarboxylates both ornithine and lysine. ODC1 (SMa0680) decarboxylates only ornithine. An odc1 mutant was similar to the wild-type in ODC activity, PA production and growth. In comparison to the wild-type, an odc2 mutant had 45 % as much ODC activity and its growth rates were reduced by 42, 14 and 44 % under non-stress, salt stress or acid stress conditions, respectively. The odc2 mutant produced only trace levels of Put, Spd and HSpd. Wild-type phenotypes were restored when the mutant was grown in cultures supplemented with 1 mM Put or Spd or when the odc2 gene was introduced in trans. odc2 gene expression was increased under acid stress and reduced under salt stress and with exogenous Put or Spd. An odc1 odc2 double mutant had phenotypes similar to the odc2 mutant. These results indicate that ODC2 is the major enzyme for Put synthesis in S. meliloti and that PAs are required for normal growth in vitro.
多胺（PAs）是由碱性 l-氨基酸衍生而来的普遍存在的多阳离子，其生理作用仍在确定中。它们在固氮根瘤菌（如 Sinorhizobium meliloti）中的生物合成和功能尚未得到广泛研究。薄层层析和质谱分析表明，S. meliloti Rm8530 以游离形式产生多胺，腐胺（Put）、亚精胺（Spd）和高亚精胺（HSpd），并以与大分子结合的形式产生 nor 亚精胺（NSpd）。S. meliloti 基因组编码两个用于 Put 合成的假定鸟氨酸脱羧酶（ODC）。用纯化酶进行的活性测定表明，ODC2（SMc02983）脱羧化鸟氨酸和赖氨酸。ODC1（SMa0680）仅脱羧化鸟氨酸。odc1 突变体与野生型在 ODC 活性、PA 产生和生长方面相似。与野生型相比，odc2 突变体的 ODC 活性降低了 45%，在非胁迫、盐胁迫和酸胁迫条件下，其生长速度分别降低了 42%、14%和 44%。odc2 突变体仅产生痕量的 Put、Spd 和 HSpd。当突变体在补充了 1mM Put 或 Spd 的培养物中生长或当 odc2 基因在转导中引入时，野生型表型得到恢复。odc2 基因表达在酸胁迫下增加，在盐胁迫下和外源性 Put 或 Spd 下减少。odc1 odc2 双突变体的表型与 odc2 突变体相似。这些结果表明，ODC2 是 S. meliloti 中 Put 合成的主要酶，PA 是体外正常生长所必需的。
