Isolation and cultivation of a novel sulfate-reducing magnetotactic bacterium belonging to the genus Desulfovibrio

Abstract

Magnetotactic bacteria (MTB) synthesize magnetosomes composed of membrane-enveloped magnetite (Fe3O4) and/or greigite (Fe3S4) nanoparticles in the cells. It is known that the magnetotactic Deltaproteobacteria are ubiquitous and inhabit worldwide in the sediments of freshwater and marine environments. Mostly known MTB belonging to the Deltaproteobacteria are dissimilatory sulfate-reducing bacteria that biomineralize bullet-shaped magnetite nanoparticles, but only a few axenic cultures have been obtained so far. Here, we report the isolation, cultivation and characterization of a dissimilatory sulfate-reducing magnetotactic bacterium, which we designate “strain FSS-1”. We found that the strain FSS-1 is a strict anaerobe and uses casamino acids as electron donors and sulfate as an electron acceptor to reduce sulfate to hydrogen sulfide. The strain FSS-1 produced bullet-shaped magnetite nanoparticles in the cells and responded to external magnetic fields. On the basis of 16S rRNA gene sequence analysis, the strain FSS-1 is a member of the genus Desulfovibrio, showing a 96.7% sequence similarity to Desulfovibrio putealis strain B7-43T. Futhermore, the magnetosome gene cluster of strain FSS-1 was different from that of Desulfovibrio magneticus strain RS-1. Thus, the strain FSS-1 is considered to be a novel sulfate-reducing magnetotactic bacterium belonging to the genus Desulfovibrio.

Fundidesulfovibrio magnetotacticus sp. nov., a sulphate-reducing magnetotactic bacterium, isolated from sediments and freshwater of a pond

“…Sediments together with freshwater were collected from Suwa Pond in Hidaka, Saitama, Japan (35.892173°N, 139.367665°E) in June 2017, and transferred to 2 l plastic bottles [37]. MTB cells were collected by neodymium–iron–boron magnets (diameter, 10×10 mm) of 480 mT attached to the outer surface of the bottles 1 cm above the sediment–water interface for 60 min, and then the cells accumulated by the magnets were collected with a Pasteur pipette.…”

“…The genome was annotated using Prokka version 1.12 with the exception of the genes encoding magnetosome proteins [50]. The magnetosome genes were annotated manually using blast x of the NCBI blast tools [37]. The draft genome sequence of strain FSS-1 T was deposited in the DDBJ/EMBL/GenBank database under the following accession numbers: BLTE01000001–BLTE01000058.…”

“…The MTB cells were then magnetically enriched by an MTB trap device for 120 min [38]. To cultivate and isolate sulphate-reducing magnetotactic bacteria, we used magnetotactic Desulfovibrio (MD) medium [37], which was composed of 0.5 ml l −1 modified Wolfe's mineral elixir [39,40], 0.5 mg l −1 resazurin, 0.25 g l −1 NH 4 Cl, 0.1 g l −1 MgSO 4 •7H 2 O, 0.1 g l −1 casamino acids (Becton, Dickinson and Company) and 0.02 g l −1 yeast extract (Becton, Dickinson and Company), and the medium was adjusted to pH 7.0. The modified Wolfe's mineral elixir contained the following salts (per litre of distilled water): 15.0 g nitrilotriacetic acid, 30.…”

Heating ability of elongated magnetic nanoparticles

“…Furthermore, oriented assemblies of nanoparticles showed increased SAR [ 37 – 38 ] when the ac magnetic field was applied parallel to the assembly orientation axis. It is worth mentioning that, in nature, some strains of magnetotactic bacteria can synthesize elongated magnetic nanoparticles [ 39 – 41 ]. Biogenic magnetic nanoparticles have a perfect crystal structure and narrow size distribution, which makes them potential agents for magnetic hyperthermia [ 27 , 42 ].…”

Heating ability of elongated magnetic nanoparticles

“…Furthermore, the oriented assembly of nanoparticles showed increased SAR [37,38] when ac magnetic field is applied parallel to the orientation axis. It is worth mentioning that in nature, some strains of magnetotactic bacteria can synthesize elongated magnetic nanoparticles [39][40][41]. Biogenic magnetic nanoparticles have a perfect crystal structure and narrow size distribution, which makes them potential agents for magnetic hyperthermia [27,42].…”