The purple bacterium Rhodobacter capsulatus is unique among Rhodobacteriacae as it contains a putative iron response regulator (Irr) but does not possess a copy of the ferric uptake regulator (Fur). Interestingly, an in-frame deletion mutant of Irr shows no major role in iron homeostasis. Instead, we showed that the previously identified activator of haem gene expression HbrL is a crucial regulator of iron homeostasis. We demonstrated that an HbrL deletion strain is unable to grow in iron-limited medium in aerobic, semi-aerobic and photosynthetic conditions and that suppressor strains can be isolated with mutations in iron uptake genes. Gene expression studies revealed that HbrL is a transcriptional activator of multiple ferrous and ferric iron uptake systems in addition to a haem uptake system. Finally, HbrL activates the expression of numerous haem biosynthesis genes. Thus, HbrL has a central role in controlling the amount of iron transport in conjunction with the synthesis of its cognate tetrapyrrole haem.

译文

:紫色细菌荚膜红细菌在红细菌中是独特的,因为它含有推定的铁反应调节剂(Irr),但不具有铁摄取调节剂(Fur)的副本。有趣的是,Irr的框内缺失突变体在铁稳态中没有主要作用。相反,我们表明先前鉴定的血红素基因表达HbrL激活剂是铁稳态的关键调节剂。我们证明了HbrL缺失菌株不能在有氧,半需氧和光合作用条件下的铁限制培养基中生长,并且可以分离出具有铁摄取基因突变的抑制菌株。基因表达研究表明,除血红素摄取系统外,HbrL还是多种亚铁和三价铁摄取系统的转录激活因子。最后,HbrL激活众多血红素生物合成基因的表达。因此,HbrL及其同源四吡咯血红素的合成在控制铁的运输中起着中心作用。

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