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

Abstract

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.

Keywords:

• Shewanella
• metals
• membrane biochemistry
• STXM
• NEXAFS

Acknowledgments

We thank Dianne Moyles for TEM advice and support, and Professors Susan Koval and John Dutcher for their insight. We also thank Brandy Toner for providing the Mn standard materials, and Tolek Tyliszczak and David Kilcoyne for support at ALS beamlines 11.0.2 and 5.3.2. We offer special thanks to the late Professor Terry Beveridge for CN32 cultures and advice. This work was supported by the Advanced Food and Materials Network, as well as the National Sciences and Engineering Research Council. The Advanced Light Source and work at BL11.0.2 and 5.3.2 is supported by the Office of Basic Energy Sciences, Division of Materials Sciences, Division of Chemical Sciences, Geosciences, and Biosciences of the DOE at Lawrence Berkeley National Laboratory under contract DE-AC02-05CH11231.