Redox-reactive membrane vesicles produced by Shewanella.

Dissimilatory iron reducing bacteria produce and release membrane vesicles with diameters ranging from 50 to 250 nm. The vesicles, which arise from the outer membrane of these Gram-negative bacteria, lack DNA but contain proteins that catalyze the reduction of ferric iron and other multivalent heavy metals and radionuclides. This enzymatic process results in the formation of nano-size biogenic mineral assemblages that resemble nanofossils. Under low-shear conditions, membrane vesicles are commonly tethered to intact cells by electrically conductive filaments known as bacterial nanowires. The functional role of membrane vesicles and associated nanowires is not known, but the potential for mineralized vesicles that morphologically resemble nanofossils to serve as paleontological indicators of early life on earth and as biosignatures of like on other planets is recognized.