As the fourth most abundant elements in the Earth's crust, iron is a metal essential for all cellular life. However, for pathogenic bacteria invading into the tissues of host animals or plants, iron limitation is always a fatal environmental stress since the hosts tightly “catch” iron by chelating this metal with proteins or small molecular chemicals. Therefore, bacteria have to detect iron limitation and respond efficiently to be survival during the struggle of life.

Prof. QIAN Wei’s Lab at the Institute of Microbiology of Chinese Academy of Sciences has focused on how bacterium senses chemical or physical signals in the outside world. They found that in a plant pathogenic bacterium which causes black rot disease in cruciferous plants, a two-component signaling system VgrS-VgrR plays an important role in detecting iron limitation. The research article has been published in PLoS Pathogens.

VgrS is a cell-surface receptor. After detecting iron limitation, the receptor is activated and then phosphorylates the cognate VgrR which controls the uptake of iron from environment into bacterial cells. Among the downstream genes that are regulated by VgrR, the expression of a transporter, TdvA, seems detrimental to the bacterial virulence and iron uptake, and thus its transcription has to be repressed by the activated VgrR.

However, with the accumulation of intracellular iron, VgrR specifically binds to the excessive iron and this binding event leads to disassociation of the regulatory relationship between VgrR and downstream genes. The process then stops the continuous iron uptake and avoids toxic effect of excessive iron. Therefore, VgrS-VgrR is one of the simple but elegant regulatory machinery employed by the pathogenic bacterium to detect extracytoplasmic iron scarcity and intracellular iron excess.

The work was financially supported by the Strategic Priority Research Program of the Chinese Academy of Sciences, the National Natural Science Foundation of China.