Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, USA.
Arch Microbiol. 2010 Nov;192(11):899-908. doi: 10.1007/s00203-010-0620-6. Epub 2010 Aug 25.
Nitrosomonas europaea has a single three-gene operon (nitABC) encoding an iron ABC transporter system (NitABC). Phylogenetic analysis clustered the subunit NitB with Fe(3+)-ABC transporter permease components from other organisms. The N. europaea strain deficient in nitB (nitB::kan) grew well in either Fe-replete or Fe-limited media and in Fe-limited medium containing the catecholate-type siderophore, enterobactin or the citrate-based dihydroxamate-type siderophore, aerobactin. However, the nitB::kan mutant strain was unable to grow in Fe-limited media containing either the hydroxamate-type siderophores, ferrioxamine and ferrichrome or the mixed-chelating type siderophore, pyoverdine. Exposure of N. europaea cells to a ferrichrome analog coupled to the fluorescent moiety naphthalic diimide (Fhu-NI) led to increase in fluorescence in the wild type but not in nitB::kan mutant cells. Spheroplasts prepared from N. europaea wild type exposed to Fhu-NI analog retained the fluorescence, while spheroplasts of the nitB::kan mutant were not fluorescent. NitABC transports intact Fe(3+)-ferrichrome complex into the cytoplasm and is an atypical ABC type iron transporter for Fe(3+) bound to ferrioxamine, ferrichrome or pyoverdine siderophores into the cytoplasm. The mechanisms to transport iron in either the Fe(3+) or Fe(2+) forms or Fe(3+) associated with enterobactin or aerobactin siderophores into the cell across the cytoplasmic membrane are as yet undetermined.
欧洲亚硝化单胞菌有一个单一的三基因操纵子（nitABC），编码一个铁 ABC 转运系统（NitABC）。系统发育分析将亚基 NitB 与其他生物体的 Fe(3+)-ABC 转运体通透酶成分聚类在一起。缺乏 nitB 的 N. europaea 菌株（nitB::kan）在富含铁或缺铁的培养基以及含有儿茶酚型铁载体、肠菌素或基于柠檬酸的二羟肟酸型铁载体、aerobactin 的缺铁培养基中生长良好。然而，nitB::kan 突变株无法在含有羟肟酸型铁载体、ferrioxamine 和 ferrichrome 或混合螯合型铁载体、pyoverdine 的缺铁培养基中生长。将与荧光部分萘二酰亚胺偶联的 ferrichrome 类似物暴露于 N. europaea 细胞中导致野生型细胞荧光增加，但 nitB::kan 突变细胞则没有。用 ferrichrome 类似物处理后制备的 N. europaea 野生型原生质体保留荧光，而 nitB::kan 突变体的原生质体则没有荧光。NitABC 将完整的 Fe(3+)-ferrichrome 复合物转运到细胞质中，是一种将 Fe(3+)与 ferrioxamine、ferrichrome 或 pyoverdine 铁载体结合的非典型 ABC 型铁转运体转运到细胞质中。将铁以 Fe(3+)或 Fe(2+)形式或以与肠菌素或 aerobactin 铁载体结合的形式运输到细胞内穿过细胞质膜的机制尚不清楚。
