Pickering Brad S, Oresnik Ivan J
Department of Microbiology, University if Manitoba, Winnipeg, MB, R3T 2N2, Canada.
J Bacteriol. 2008 Oct;190(19):6409-18. doi: 10.1128/JB.00757-08. Epub 2008 Jul 25.
It was found that S. meliloti strain SmA818, which is cured of pSymA, could not grow on defined medium containing only formate and bicarbonate as carbon sources. Growth experiments showed that Rm1021 was capable of formate/bicarbonate-dependent growth, suggesting that it was capable of autotrophic-type growth. The annotated genome of S. meliloti Rm1021 contains three formate dehydrogenase genes. A systematic disruption of each of the three formate dehydrogenase genes, as well as the genes encoding determinants of the Calvin-Benson-Bassham, cycle was carried out to determine which of these determinants played a role in growth on this defined medium. The results showed that S. meliloti is capable of formate-dependent autotrophic growth. Formate-dependent autotrophic growth is dependent on the presence of the chromosomally located fdsABCDG operon, as well as the cbb operon carried by pSymB. Growth was also dependent on the presence of either of the two triose-phosphate isomerase genes (tpiA or tpiB) that are found in the genome. In addition, it was found that fdoGHI carried by pSymA encodes a formate dehydrogenase that allows Rm1021 to carry out formate-dependent respiration. Taken together, the data allow us to present a model of how S. meliloti can grow on defined medium containing only formate and bicarbonate as carbon sources.
研究发现，缺失pSymA的苜蓿中华根瘤菌菌株SmA818无法在仅含有甲酸盐和碳酸氢盐作为碳源的限定培养基上生长。生长实验表明，Rm1021能够进行依赖甲酸盐/碳酸氢盐的生长，这表明它能够进行自养型生长。苜蓿中华根瘤菌Rm1021的注释基因组包含三个甲酸脱氢酶基因。对这三个甲酸脱氢酶基因以及编码卡尔文-本森-巴斯姆循环决定因素的基因进行了系统性破坏，以确定这些决定因素中哪些在这种限定培养基上的生长中起作用。结果表明，苜蓿中华根瘤菌能够进行依赖甲酸盐的自养生长。依赖甲酸盐的自养生长取决于染色体定位的fdsABCDG操纵子以及pSymB携带的cbb操纵子的存在。生长还取决于基因组中发现的两个磷酸丙糖异构酶基因（tpiA或tpiB）中的任何一个的存在。此外，还发现pSymA携带的fdoGHI编码一种甲酸脱氢酶，该酶使Rm1021能够进行依赖甲酸盐的呼吸作用。综上所述，这些数据使我们能够提出一个关于苜蓿中华根瘤菌如何在仅含有甲酸盐和碳酸氢盐作为碳源的限定培养基上生长的模型。
