Combined Approaches for Characterization of an Uncultivated Magnetotactic coccus from Lake Miyun near Beijing

This paper reports the features of an as yet uncultivated magnetotactic coccus, named MYC-1, recently found from surface sediments of Lake Miyun near Beijing. Light microscope and Bacteriodrome analyses demonstrate that MYC-1 is north-seeking in the Earth's magnetic field. Transmission electron microscope (TEM) attached with energy-dispersive X-ray analyses reveal that this coccus contains a single chain of magnetosomes, containing approximately 10 large iron-oxide crystals. Morphology of these crystals is featured by prism with a mean length and width of 117 nm and 95 nm (statistics from 281 crystals), respectively; it yields an aspect factor of 1.24. A linear relationship (r2 = 0.83) clearly exists between the length and width of crystals. In agreement with previous results, we observed that the size distribution of the MYC-1 is distinctly asymmetric with cut off toward larger sizes, which is the opposite of non-biogenic crystals. Low-temperature magnetic measurements on bulk bacteria samples show a distinct Verwey transition temperature (Tv) around 115 K indicative of magnetite, thus the magnetosomes contain magnetite. For a field of 0.5 mT, we determined a swimming speed of approximately 141 m/s for the MYC-1. Furthermore, the magnetic moment estimated from the rotating magnetic field method is 1.8 x 10-15 Am2 per cell. Finally, this finding of freshwater magnetotactic coccus in Lake Miyun suggests that magnetite produced by the MYC-1 strain is a potentially important remanence carrier in these lake sediments.