Metals have disparate impacts on lipid mobility in Shewanella putrefaciens CN32

Bacteria are central to soil bioremediation strategies to reduce metal concentrations in soil and water. This requires the cell envelope to maintain structural integrity despite elevated concentrations of cationic. Here we investigate liposomes obtained from extracted S. putrefaciens CN32 phospholipids after culturing CN32 with Mn(II), V(IV) and U(VI), using spectrofluorometric lipid microviscosity assays. Phospholipid diffusion decreased following exposure to 0.01 mM V(IV) and Mn(II); exposure to 0.1 mM concentration decreased phospholipid diffusion for the Mn(II) treatment only. At 1 mM, V(IV) and Mn(II) fluidized the phospholipids. Sub-micron Mn particulates and diffuse Mn were observed using Scanning Transmission X-ray Microscopy (STXM), but vanadium was not detected on the envelopes.  In contrast to Mn and V, U impeded diffusion significantly at all concentrations from 0.01 to 1 mM. The mobility of membrane components is critical for bacterial survival and growth. Our results demonstrate that cationic Mn, V and U impose strong abiotic effects on membrane lipid dynamics.