Department of Biology, New England College, Henniker, NH, USA.
Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, NH, USA.
J Oral Microbiol. 2015 Dec 16;7:29800. doi: 10.3402/jom.v7.29800. eCollection 2015.
Actinomyces oris is a Gram-positive bacterium that has been associated with healthy and diseased sites in the human oral cavity. Most pathogenic bacteria require iron to survive, and in order to acquire iron in the relatively iron-scarce oral cavity A. oris has been shown to produce iron-binding molecules known as siderophores. The genes encoding these siderophores and transporters are thought to be regulated by the amount of iron in the growth medium and by the metal-dependent repressor, AmdR, which we showed previously binds to the promoter of proposed iron-regulated genes.
The purpose of this study was to characterize siderophore and associated iron transport systems in A. oris.
We examined gene expression of the putative iron transport genes fetA and sidD in response to low- and high-iron environments. One of these genes, sidD, encoding a putative Fe ABC transporter protein, was insertionally inactivated and was examined for causing growth defects. To gain a further understanding of the role of iron metabolism in oral diseases, clinical isolates of Actinomyces spp. were examined for the presence of the gene encoding AmdR, a proposed global regulator of iron-dependent gene expression in A. oris.
When A. oris was grown under iron-limiting conditions, the genes encoding iron/siderophore transporters fetA and sidD showed increased expression. One of these genes (sidD) was mutated, and the sidD::Km strain exhibited a 50% reduction in growth in late log and stationary phase cells in media that contained iron. This growth defect was restored when the sidD gene was provided in a complemented strain. We were able to isolate the AmdR-encoding gene in seven clinical isolates of Actinomyces. When these protein sequences were aligned to the laboratory strain, there was a high degree of sequence similarity.
The growth of the sidD::Km mutant in iron-replete medium mirrored the growth of the wild-type strain grown in iron-limiting medium, suggesting that the sidD::Km mutant was compromised in iron uptake. The known iron regulator AmdR is well conserved in clinical isolates of A. oris. This work provides additional insight into iron metabolism in this important oral microbe.
口腔放线菌是一种革兰氏阳性细菌，与人类口腔的健康和患病部位有关。大多数致病菌需要铁才能存活，为了在相对缺铁的口腔环境中获取铁，口腔放线菌已被证明能产生铁结合分子，即铁载体。编码这些铁载体和转运蛋白的基因被认为受到生长培养基中铁含量的调节，以及金属依赖性阻遏物 AmdR 的调节，我们之前曾表明 AmdR 与拟调控的铁基因的启动子结合。
本研究旨在研究口腔放线菌中铁载体和相关铁转运系统的特性。
我们检测了在低铁和高铁环境下推定铁转运基因 fetA 和 sidD 的基因表达情况。这些基因中的一个，编码假定的 Fe ABC 转运蛋白的 sidD 基因，被插入失活，并检测其导致的生长缺陷。为了进一步了解铁代谢在口腔疾病中的作用，我们检测了口腔放线菌的临床分离株中 AmdR 基因的存在情况，AmdR 是口腔放线菌中铁依赖基因表达的全局调控因子。
当口腔放线菌在缺铁条件下生长时，编码铁/铁载体转运蛋白 fetA 和 sidD 的基因表达增加。其中一个基因（sidD）发生突变，sidD::Km 株在含有铁的培养基中处于对数晚期和静止期的细胞生长速度降低了 50%。当在互补菌株中提供 sidD 基因时，这种生长缺陷得到了恢复。我们能够从 7 株口腔放线菌的临床分离株中分离出编码 AmdR 的基因。当这些蛋白质序列与实验室菌株进行比对时，存在高度的序列相似性。
sidD::Km 突变株在富含铁的培养基中的生长情况与野生型菌株在缺铁培养基中的生长情况相似，这表明 sidD::Km 突变株在铁摄取方面受到了损害。已知的铁调节因子 AmdR 在口腔放线菌的临床分离株中高度保守。这项工作为该重要口腔微生物的铁代谢提供了更多的见解。
