Transcriptional response to metal starvation in the emerging pathogen Mycoplasma genitalium is mediated by Fur-dependent and –independent regulatory pathways

Transition metals participate in numerous enzymatic reactions and they are essential for survival in all living organisms. For this reason, bacterial pathogens have evolved dedicated machineries to effectively compete with their hosts and scavenge metals at the site of infection. In this study, we investigated the mechanisms controlling metal acquisition in the emerging human pathogen Mycoplasma genitalium. We observed a robust transcriptional response to metal starvation, and many genes coding for predicted lipoproteins and ABC-transporters were significantly up-regulated. Transcriptional analysis of a mutant strain lacking a metalloregulator of the Fur family revealed the activation of a full operon encoding a putative metal transporter system and a gene coding for a Histidine-rich lipoprotein (Hrl). We recognized a conserved sequence with dyad symmetry within the promoter region of the Fur-regulated genes. Mutagenesis of the predicted Fur operator within the hrl promoter abrogated Fur- and metal-dependent expression of a reporter gene. Metal starvation still impelled a strong transcriptional response in the fur mutant, demonstrating the existence of Fur-independent regulatory pathways controlling metal homeostasis. Finally, analysis of metal accumulation in the wild-type strain and the fur mutant by ICP-MS revealed an important role of Fur in nickel acquisition.

过渡金属参与众多酶促反应，并对于所有生物体的生存至关重要。鉴于此，细菌病原体已进化出专门的机制，以有效与其宿主竞争并在感染部位掠夺金属。在本研究中，我们探讨了新兴的人类病原体解脲支原体在金属获取过程中的调控机制。我们观察到对金属缺乏的转录反应强烈，许多编码预测性脂蛋白和ABC转运蛋白的基因显著上调。对缺乏Fur家族金属调节因子的突变菌株的转录分析揭示了编码假定的金属转运系统及富含组氨酸脂蛋白（Hrl）基因的完整操纵子的激活。我们在Fur调控基因的启动子区域识别出具有二联对称性的保守序列。对hrl启动子内预测的Fur操作子的突变消除了Fur和金属依赖性报告基因的表达。即使在fur突变体中，金属缺乏仍然促使强烈的转录反应，这表明存在控制金属稳态的非Fur依赖性调控途径。最后，通过ICP-MS对野生型菌株和fur突变体中金属积累的分析揭示了Fur在镍获取中的重要作用。