Developmental stage oxidoreductive states of Chlamydia and infected host cells.

Infectious Chlamydia organisms have highly oxidized and cysteine cross-linked membrane proteins that confer environmental stability when outside their host cells. Once these organisms infect a new host cell, the proteins become reduced and remain reduced during the active growth stage. These proteins become oxidized at the end of their growth cycle, wherein infectious organisms are produced and released to the environment. How chlamydiae mediate and regulate this key step in their pathogenesis is unknown. Using biosensors specifically targeted to different compartments within the infected host cell and for the chlamydial organisms themselves, the oxidoreductive states of these compartments were measured during the course of infection. We found that the host cell redox states are not changed by infection with C. trachomatis, whereas the state of the chlamydial organisms remains reduced during infection until the late developmental stages, wherein the organisms' cytosol and periplasm become oxidized and they acquire environmental resistance and infectivity.