Department of Microbiology, University of Georgia, Athens, GA 30602, USA.
Environ Microbiol. 2011 Nov;13(11):2855-64. doi: 10.1111/j.1462-2920.2011.02558.x. Epub 2011 Aug 30.
Although it is accepted that bacteria-colonizing host tissues are commonly faced with iron-limiting conditions and that pathogenic bacteria often utilize iron from host-derived haem-based compounds, the mechanisms of iron acquisition by beneficial symbiotic bacteria are less clear. The bacterium Vibrio fischeri mutualistically colonizes the light organ of the squid Euprymna scolopes. Genome sequence analysis of V. fischeri revealed a putative haem-uptake gene cluster, and through mutant analysis we confirmed this cluster is important for haemin use by V. fischeri in culture. LacZ reporter assays demonstrated Fur-dependent transcriptional regulation of cluster promoter activity in culture. GFP-based reporter assays revealed that gene cluster promoter activity is induced in symbiotic V. fischeri as early as 14 h post inoculation, although colonization assays with the haem uptake mutant suggested an inability to uptake haem does not begin to limit colonization until later stages of the symbiosis. Our data indicate that the squid light organ is a low iron environment and that haem-based sources of iron are used by symbiotic V. fischeri cells. These findings provide important additional information on the availability of iron during symbiotic colonization of E. scolopes by V. fischeri, as well as the role of haem uptake in non-pathogenic host-microbe interactions.
尽管人们普遍认为，定植于宿主组织的细菌常常面临缺铁条件，而致病菌通常会从宿主来源的血红素基化合物中获取铁，但有益共生细菌获取铁的机制还不太清楚。细菌 Vibrio fischeri 与鱿鱼 Euprymna scolopes 的发光器官共生。对 V. fischeri 的基因组序列分析揭示了一个可能的血红素摄取基因簇，通过突变分析，我们证实该簇对于 V. fischeri 在培养物中利用血红素至关重要。 LacZ 报告基因测定表明，在培养物中，该簇启动子的活性受到 Fur 依赖性转录调控。GFP 报告基因测定显示，共生 V. fischeri 中的基因簇启动子活性早在接种后 14 小时就被诱导，但用血红素摄取突变体进行的定植实验表明，血红素摄取能力的丧失直到共生关系的后期才开始限制定植。我们的数据表明，鱿鱼的发光器官是一个低铁环境，共生的 V. fischeri 细胞利用血红素基铁源。这些发现为 Vibrio fischeri 共生定植期间铁的可用性以及血红素摄取在非致病性宿主-微生物相互作用中的作用提供了重要的补充信息。
