Precipitation of Iron on the Surface of Leptospira interrogans Is Associated with Mutation of the Stress Response Metalloprotease HtpX

Abstract

ABSTRACTHigh concentrations of free metal ions in the environment can be detrimental to bacterial survival. However, bacteria utilize strategies, including the activation of stress response pathways and immobilizing chemical elements on their surface, to limit this toxicity. In this study, we characterized LA4131, the HtpX-like M48 metalloprotease fromLeptospira interrogans, with a putative role in bacterial stress response and membrane homeostasis. Growth of thela4131transposon mutant strain (L522) in 360 μM FeSO4(10-fold the normalin vitroconcentration) resulted in the production of an amorphous iron precipitate. Atomic force microscopy and transmission electron microscopy analysis of the strain demonstrated that precipitate production was associated with the generation and release of outer membrane vesicles (OMVs) from the leptospiral surface. Transcriptional studies indicated that inactivation ofla4131resulted in altered expression of a subset of metal toxicity and stress response genes. Combining these findings, this report describes OMV production in response to environmental stressors and associates OMV production with thein vitroactivity of an HtpX-like metalloprotease.