Dunn Anne K, Stabb Eric V
Department of Microbiology, University of Georgia, Athens, Georgia 30602, USA.
J Bacteriol. 2008 Sep;190(17):5814-23. doi: 10.1128/JB.00227-08. Epub 2008 Jul 7.
Trimethylamine N-oxide (TMAO) reductases are widespread in bacteria and often function in anaerobic respiration. The regulation and expression of TMAO reductase operons have been well studied in model genera such as Escherichia, Shewanella, and Rhodobacter, although TMAO reductases are present in many other bacteria, including the marine Vibrio species. The genome sequence of Vibrio fischeri revealed three putative TMAO reductase operons, and a previous report identified TMAO reductase activity in symbiotic V. fischeri isolates associated with the light organs of adult Hawaiian bobtail squid, Euprymna scolopes. We examined the roles and regulation of these three operons using mutational analyses and promoter-reporter fusions. We found that the torECA promoter, and to a lesser extent the torYZ and dmsABC promoters, were active during symbiotic colonization of juvenile E. scolopes; however, a V. fischeri strain lacking TMAO reductase activity displays no discernible colonization defect over the first 48 h. Our studies also revealed that torECA has the most active promoter of the putative TMAO reductase operons, and TorECA is the major contributor to TMAO-dependent growth in V. fischeri under the conditions tested. Interestingly, the transcriptional regulation of TMAO reductase operons in V. fischeri appears to differ from that in previously studied organisms, such as Escherichia coli, which may reflect differences in gene arrangement and bacterial habitat. This study lays the foundation for using V. fischeri as a model system for studying TMAO reductases in the Vibrionaceae.
三甲胺N-氧化物(TMAO)还原酶在细菌中广泛存在,且常在厌氧呼吸中发挥作用。尽管包括海洋弧菌属物种在内的许多其他细菌中都存在TMAO还原酶,但在诸如大肠杆菌、希瓦氏菌属和红杆菌属等模式菌属中,对TMAO还原酶操纵子的调控和表达已有深入研究。费氏弧菌的基因组序列显示有三个假定的TMAO还原酶操纵子,之前的一份报告在与成年夏威夷短尾乌贼(Euprymna scolopes)发光器官相关的共生费氏弧菌分离物中鉴定出了TMAO还原酶活性。我们使用突变分析和启动子-报告基因融合技术研究了这三个操纵子的作用和调控。我们发现,torECA启动子,以及程度稍低的torYZ和dmsABC启动子,在幼年短尾乌贼的共生定殖过程中具有活性;然而,一株缺乏TMAO还原酶活性的费氏弧菌菌株在最初48小时内没有明显的定殖缺陷。我们的研究还表明,torECA在假定的TMAO还原酶操纵子中具有最活跃的启动子,并且在测试条件下,TorECA是费氏弧菌中TMAO依赖生长的主要贡献者。有趣的是,费氏弧菌中TMAO还原酶操纵子的转录调控似乎与之前研究的生物体(如大肠杆菌)不同,这可能反映了基因排列和细菌栖息地的差异。这项研究为将费氏弧菌用作研究弧菌科中TMAO还原酶的模型系统奠定了基础。