Franck William L, Chang Woo-Suk, Qiu Jing, Sugawara Masayuki, Sadowsky Michael J, Smith Stephanie A, Stacey Gary
National Center for Soybean Biotechnology, Division of Plant Sciences, University of Missouri, Columbia, Missouri 65211, USA.
J Bacteriol. 2008 Oct;190(20):6697-705. doi: 10.1128/JB.00543-08. Epub 2008 Aug 8.
Bradyrhizobium japonicum is a facultative chemoautotroph capable of utilizing hydrogen gas as an electron donor in a respiratory chain terminated by oxygen to provide energy for cellular processes and carbon dioxide assimilation via a reductive pentose phosphate pathway. A transcriptomic analysis of B. japonicum cultured chemoautotrophically identified 1,485 transcripts, representing 17.5% of the genome, as differentially expressed when compared to heterotrophic cultures. Genetic determinants required for hydrogen utilization and carbon fixation, including the uptake hydrogenase system and components of the Calvin-Benson-Bassham cycle, were strongly induced in chemoautotrophically cultured cells. A putative isocitrate lyase (aceA; blr2455) was among the most strongly upregulated genes, suggesting a role for the glyoxylate cycle during chemoautotrophic growth. Addition of arabinose to chemoautotrophic cultures of B. japonicum did not significantly alter transcript profiles. Furthermore, a subset of nitrogen fixation genes was moderately induced during chemoautotrophic growth. In order to specifically address the role of isocitrate lyase and nitrogenase in chemoautotrophic growth, we cultured aceA, nifD, and nifH mutants under chemoautotrophic conditions. Growth of each mutant was similar to that of the wild type, indicating that the glyoxylate bypass and nitrogenase activity are not essential components of chemoautotrophy in B. japonicum.
日本慢生根瘤菌是一种兼性化学自养菌，能够在以氧气为终端的呼吸链中利用氢气作为电子供体，为细胞过程提供能量，并通过还原性戊糖磷酸途径进行二氧化碳同化。对化学自养培养的日本慢生根瘤菌进行的转录组分析确定，与异养培养相比，有1485个转录本（占基因组的17.5%）差异表达。在化学自养培养的细胞中，氢气利用和碳固定所需的遗传决定因素，包括摄取氢化酶系统和卡尔文-本森-巴斯姆循环的成分，被强烈诱导。一个假定的异柠檬酸裂合酶（aceA；blr2455）是上调最强烈的基因之一，表明乙醛酸循环在化学自养生长过程中发挥作用。向日本慢生根瘤菌的化学自养培养物中添加阿拉伯糖并没有显著改变转录本图谱。此外，一部分固氮基因在化学自养生长过程中受到适度诱导。为了具体研究异柠檬酸裂合酶和固氮酶在化学自养生长中的作用，我们在化学自养条件下培养了aceA、nifD和nifH突变体。每个突变体的生长与野生型相似，这表明乙醛酸旁路和固氮酶活性不是日本慢生根瘤菌化学自养的必需成分。
