Two genera of magnetococci with bean-like morphology from intertidal sediments of the Yellow Sea, China.

Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China.
Applied and Environmental Microbiology (Impact Factor: 3.95). 06/2012; 78(16):5606-11. DOI: 10.1128/AEM.00081-12
Source: PubMed

ABSTRACT Magnetotactic bacteria have the unique capacity of being able to swim along geomagnetic field lines. They are Gram-negative bacteria with diverse morphologies and variable phylogenetic relatedness. Here, we describe a group of uncultivated marine magnetococci collected from intertidal sediments of Huiquan Bay in the Yellow Sea. They were coccoid-ovoid in morphology, with an average size of 2.8 ± 0.3 μm by 2.0 ± 0.2 μm. Differential interference contrast microscopy, fluorescence microscopy, and transmission electron microscopy revealed that each cell was apparently composed of two hemispheres. The cells synthesized iron oxide-type magnetosomes that clustered on one side of the cell at the interface between the two hemispheres. In some cells two chains of magnetosomes were observed across the interface. Each cell had two bundles of flagella enveloped in a sheath and displayed north-seeking helical motion. Two 16S rRNA gene sequences having 91.8% identity were obtained, and their authenticity was confirmed by fluorescence in situ hybridization. Phylogenetic analysis revealed that the magnetococci are affiliated with the Alphaproteobacteria and are most closely related to two uncultured magnetococci with sequence identities of 92.7% and 92.4%, respectively. Because they display a >7% sequence divergence to all bacteria reported, the bean-like magnetococci may represent two novel genera.

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    ABSTRACT: Two morphotypes of multicellular magnetotactic prokaryotes (MMPs) have been identified: spherical (several species) and ellipsoidal (previously one species). Here, we report novel ellipsoidal MMPs that are ∼10 × 8 μm in size, and composed of about 86 cells arranged in six to eight interlaced circles. Each MMP was composed of cells that synthesized either bullet-shaped magnetite magnetosomes alone, or both bullet-shaped magnetite and equidimensional greigite magnetosomes. They showed north-seeking magnetotaxis, ping-pong motility, and negative phototaxis at a velocity up to 300 μm s-1. During reproduction, they divided along either their long- or short- body axes. For genetic analysis, we sorted the ellipsoidal MMPs with micromanipulation, and amplified their genomes using multiple displacement amplification. We sequenced the 16S rRNA gene and found 6.9% sequence divergence from that of ellipsoidal MMPs, Candidatus Magnetananas tsingtaoensis, and > 8.3% divergence from those of spherical MMPs. Therefore, the novel MMPs belong to different species and genus compared to the currently known ellipsoidal and spherical MMPs, respectively. The novel MMPs display a morphological cell differentiation, implying a potential division of labor. These findings provide new insights into the diversity of MMPs in general, and contribute to our understanding of the evolution of multicellularity among prokaryotes.
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