FIGURE 3.

Regulatory and metabolic network related to As(III) oxidation. Under Pi-starvation and arsenic-enriched conditions, AioX and PstS sense the As(III) and As(V)/Pi signal first, and then AioS and PhoR are autophosphorylated. AioR and PhoB1 are phosphorylated by both AioS and PhoR. AioR positively regulates the expression of the As(III) oxidase AioBA and suppresses the TCA cycle so that As(III) oxidation is the main energy resource. Moreover, AioR increases the expression of the ars operon to enhance bacterial As(III) efflux. Moreover, ArsR activates the pst1/pho1 system, while AioR restrains the pst2/pho2 system to transport Pi and As(V). PhoB1 also increases the expression of the aio gene cluster and pst1/pho1 system. The connected regulatory network between the Aio, Ars and Pst/Pho systems indicates the close relationship between As(III) oxidation, As(III) efflux and Pi uptake. Furthermore, AioR regulates the expression of mcp and helps bacteria move toward As(III) to produce more energy and As(V). The synthesis of arsenolipids containing As(V) may spare Pi for nucleic acid synthesis, thereby enhancing bacterial survival potential. These findings imply that As(III) oxidation is biologically part of the Pi-starvation response.