Department of Microbiology, University of Manitoba, Winnipeg, Manitoba, Canada.
J Bacteriol. 2012 Sep;194(18):5044-53. doi: 10.1128/JB.00982-12. Epub 2012 Jul 13.
A mutant unable to utilize galactose was isolated in Sinorhizobium meliloti strain Rm1021. The mutation was found to be in a gene annotated dgoK1, a putative 2-keto-3-deoxygalactonokinase. The genetic region was isolated on a complementing cosmid and subsequently characterized. Based on genetic and bioinformatic evidence, the locus encodes all five enzymes (galD, dgoK, dgoA, SMc00883, and ilvD1) involved in the De Ley-Doudoroff pathway for galactose catabolism. Although all five genes are present, genetic analysis suggests that the galactonase (SMc00883) and the dehydratase (ilvD1) are dispensable with respect to the ability to catabolize galactose. In addition, we show that the transport of galactose is partially facilitated by the arabinose transporter (AraABC) and that both glucose and galactose compete with arabinose for transport. Quantitative reverse transcription-PCR (qRT-PCR) data show that in a dgoK background, the galactose locus is constitutively expressed, and the induction of the ara locus seems to be enhanced. Assays of competition for nodule occupancy show that the inability to catabolize galactose is correlated with an increased ability to compete for nodule occupancy.
在苜蓿中华根瘤菌 Rm1021 中分离到一株不能利用半乳糖的突变体。该突变被发现位于一个注释为 dgoK1 的基因中，该基因推测为 2-酮-3-脱氧半乳糖激酶。该基因区域被分离在一个互补的 cosmid 上，并随后进行了表征。基于遗传和生物信息学证据，该基因座编码参与半乳糖分解代谢的 De Ley-Doudoroff 途径的所有五种酶（galD、dgoK、dgoA、SMc00883 和 ilvD1）。尽管存在所有五个基因，但遗传分析表明，半乳糖酶（SMc00883）和脱水酶（ilvD1）对于半乳糖的分解代谢能力是可有可无的。此外，我们还表明，半乳糖的运输部分由阿拉伯糖转运蛋白（AraABC）促进，并且葡萄糖和半乳糖都与阿拉伯糖竞争运输。定量反转录-PCR（qRT-PCR）数据显示，在 dgoK 背景下，半乳糖基因座持续表达，ara 基因座的诱导似乎增强。对竞争结瘤占据的测定表明，不能分解半乳糖与增加竞争结瘤占据的能力相关。
