Hayashida Hideaki, Poulsen Knud, Kilian Mogens
Division of Oral Health Services Research, Department of Public Health, Nagasaki University Graduate School of Biomedical Sciences, 1-7-1 Sakamoto, Nagasaki 852-8588, Japan2.
Department of Medical Microbiology and Immunology, University of Aarhus, the Bartholin Building, DK-8000 Aarhus C, Denmark1.
Microbiology (Reading). 2002 Dec;148(Pt 12):3993-4001. doi: 10.1099/00221287-148-12-3993.
To get a better insight into the physiology of the high-toxic JP2 clone of Actinobacillus actinomycetemcomitans serotype b, which is strongly associated with juvenile periodontitis in adolescents of African descent, the modes of iron acquisition in this clone were examined and compared to those of other strains of the species. None of the strains examined could utilize human transferrin as a source of iron. This was in accordance with the presence of a non-functional tbpA gene, which normally encodes the A subunit of the transferrin-binding-protein complex. Southern blot analysis indicated that functional duplications of tbpA were not present in the genome. Thus, A. actinomycetemcomitans seems to be in a process of evolution, in which iron acquisition from host transferrin is not essential as in many other members of the pasteurellaceae. All strains could utilize haem as a source of iron. All 11 A. actinomycetemcomitans strains examined harboured a single genomic sequence with homology to the hgpA gene encoding haemoglobin-binding protein A in Haemophilus influenzae. However, in all three strains belonging to the JP2 clone and in one serotype e strain hgpA was a pseudogene. Seven other strains possessed a functional hgpA gene which, according to insertion mutagenesis experiments, was responsible for the ability of these strains to utilize haemoglobin as a source of iron. Thus, the presence of an hgpA pseudogene and the inability to use human haemoglobin as an iron source discriminate the high-toxic JP2 clone from low-toxic serotype b strains and most other strains of A. actinomycetemcomitans.
为了更深入了解放线共生放线杆菌b血清型高毒性JP2克隆株的生理学特性（该克隆株与非洲裔青少年的青少年牙周炎密切相关），研究了该克隆株获取铁的方式，并与该物种的其他菌株进行了比较。所检测的菌株均不能利用人转铁蛋白作为铁源。这与存在无功能的tbpA基因一致，该基因通常编码转铁蛋白结合蛋白复合物的A亚基。Southern印迹分析表明基因组中不存在tbpA的功能重复。因此，放线共生放线杆菌似乎正处于进化过程中，在这个过程中，从宿主转铁蛋白获取铁不像巴斯德菌科的许多其他成员那样必不可少。所有菌株都可以利用血红素作为铁源。所检测的11株放线共生放线杆菌均含有一个与流感嗜血杆菌中编码血红蛋白结合蛋白A的hgpA基因具有同源性的单一基因组序列。然而，在属于JP2克隆的所有三株菌株和一株e血清型菌株中，hgpA是一个假基因。其他七株菌株拥有功能性hgpA基因，根据插入诱变实验，该基因负责这些菌株利用血红蛋白作为铁源的能力。因此，hgpA假基因的存在以及无法利用人血红蛋白作为铁源，将高毒性的JP2克隆株与低毒性的b血清型菌株及大多数其他放线共生放线杆菌菌株区分开来。
