Implication of exofacial thiol groups in the reducing activity ofListeria monocytogenes

Listeria monocytogenes growing in BHI in anaerobic condition leads a decrease of redox potential at pH7 ( E h7 ) from 0 to −250 mV. An investigation of mechanisms involved in this reducing activity shows the implication of thiol groups located on the bacterial cell surface. Indeed, after reduction of media to −250 mV, only thiol-reactive reagents could restore the initial E h7 value. Moreover, the growth of L. monocytogenes in anaerobic condition is characterized by a reduction then acidification phases. This suggests a sensor mechanism of environmental E h7 to convert the metabolism way from the first phase to the second. Finally, the concentration of exofacial thiol still increase strongly during the acidification phase of L. monocytogenes , even after reach the minimal value of E h7 . These results suggest that maintaining the exofacial thiol (−SH) groups in a reduced state do not depend on an active mechanism. Thiol groups appear to be displayed by membrane proteins or cell wallbound proteins and may participate in protecting cells against oxidative stress.