Changes in Shewanella putrefaciens CN32 Membrane Stability upon Growth in the Presence of Soluble Mn(II), V(IV), and U(VI)

In natural reducing environments, such as anoxic sediments and soils, bacteria may be exposed to high concentrations of soluble transition metals. The aim of this study was to identify physiological and biochemical adaptations of Shewanella putrefaciens CN32 membranes to soluble Mn(II), V(IV), and U(VI). We assessed responses of CN32 to these metals, in aerobic and anaerobic cultures, by means of membrane fluidity and fatty acid composition assays. During aerobic growth, all metals had a stabilizing effect on fluidity, while under anoxic conditions this was only observed for bacteria treated with U(VI). Membrane gel-to-fluid phase transition temperatures were higher under anaerobic conditions and were not affected by the metal treatments. Fatty acid desaturation demonstrated linear correlation with significant increases in membrane fluidity, despite metal treatments that did not significantly alter fatty acid chemistry. Scanning transmission X-ray microscopy (STXM) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS) at Mn 2p- and V 2p-edges revealed that both Mn(II) and V(IV) were associated with CN32 membranes, with V(IV) associating as VO²⁺ under anoxic conditions only. The results of this study indicate that the bacterial growth environment greatly impacts membrane chemistry and stability, with overall implications for in vitro as well as in situ studies. Supplemental materials are available for this article. Please go to the publisher's online edition of Geomicrobiology Journal to view the supplemental file.