Magnetic Bacteria as a Tool for Bioremediation of Heavy Metal Ion

Magnetotactic bacteria (MTB) are microorganism found in lake sediments and have a chain like organelle called magnetosome which is composed of highly pure crystal of magnetite (Fe3O4). We culturedMagnetospirillum magnetotacticum(MS-1) with culture media containing heavy metal ions such as Fe (standard media), Fe/Zn or Fe/Co and study on a possibility of MTB as a tool for bioremediation. In culture media containing Fe, Fe/Zn or Fe/Co, the growth rate of the bacteria was almost same. We measured the magnetic properties of the dried cells. The saturation magnetization (Ms) and the saturation remanence (Mr) of MS-1 cultured in Fe/Zn or Fe/Co media were decreased, but the coercivity (Hc) and the coercivity remanence (Hr) were increased from those of MS-1 cultured in the Fe media. The value ofMr/MsandHr/Hcwere ca. 0.5 and ca. 1.0, respectively. The changes in the magnetic properties of MS-1 cultured in Fe/Zn or Fe/Co media represent that MS-1 would take not only Fe, but also Zn or Co element in their environment. We discuss about a possible usage and advantages of MTB as a tool for bioremediation.

Magnetospirillum bellicus sp. nov., a Novel Dissimilatory Perchlorate-Reducing Alphaproteobacterium Isolated from a Bioelectrical Reactor

ABSTRACT Previously isolated dissimilatory perchlorate-reducing bacteria (DPRB) have been primarily affiliated with the Betaproteobacteria. Enrichments from the cathodic chamber of a bioelectrical reactor (BER) inoculated from creek water in Berkeley, CA, yielded a novel organism most closely related to a previously described strain, WD (99% 16S rRNA gene identity). Strain VDYT has 96% 16S rRNA gene identity to both Magnetospirillum gryphiswaldense and Magnetospirillum magnetotacticum, and along with strain WD, distinguishes a clade of perchlorate-reducing Magnetospirillum species in the Alphaproteobacteria. In spite of the phylogenetic location of VDYT, attempted PCR for the key magnetosome formation genes mamI and mamL was negative. Strain VDYT was motile, non-spore forming, and, in addition to perchlorate, could use oxygen, chlorate, nitrate, nitrite, and nitrous oxide as alternative electron acceptors with acetate as the electron donor. Transient chlorate accumulation occurred during respiration of perchlorate. The organism made use of fermentation end products, such as acetate and ethanol, as carbon sources and electron donors for heterotrophic growth, and in addition, strain VDYT could grow chemolithotrophically with hydrogen serving as the electron donor. VDYT contains a copy of the RuBisCo cbbM gene, which was expressed under autotrophic but not heterotrophic conditions. DNA-DNA hybridization with strain WD confirmed VDYT as a separate species (46.2% identity), and the name Magnetospirillum bellicus sp. nov. (DSM 21662, ATCC BAA-1730) is proposed.