HR: 17:00h
AN: B24A-05    [Abstracts]
TI: Identification and enumeration of novel uncultivated marine magnetotactic bacteria
AU: * Simmons, S L
EM: sheris@mit.edu
AF: Geomicrobiology Group, Woods Hole Oceanographic Institution, MS #8, Woods Hole, MA 02543 United States
AU: Edwards, K J
EM: katrina@whoi.edu
AF: Geomicrobiology Group, Woods Hole Oceanographic Institution, MS #8, Woods Hole, MA 02543 United States
AB: Magnetotactic bacteria (MB) precipitate intracellular single domain ferromagnetic iron oxide (magnetite) or iron sulfide (greigite) minerals, causing them to respond to geomagnetic fields. MB are typically found at or below the interface between oxic and sulfidic environments, and can reach significant population densities. We have observed 10⁴ to 10⁵ magnetotactic bacterial cells per ml in Salt Pond (Falmouth, MA), a seasonally stratified shallow marine basin. We used PCR, sequencing, and catalyzed reporter deposition-in situ hybridization (CARD-FISH), to identify and enumerate three new species of marine magnetotactic bacteria in Salt Pond. These include a greigite producing rod (the first MB in the gamma Proteobacteria), a magnetite-producing coccus in the alpha Proteobacteria, and an organism with a unique chain morphology in the delta Proteobacteria (the 'barbell'). We used quantitative PCR (qPCR) to describe the population dynamics of these organisms in Salt Pond during summer 2003, in conjunction with geochemical analysis. Each organism occupied a distinct position in the water column with respect to iron and sulfur chemistry. Magnetite producing organisms were located at the redox boundary while greigite producing organisms were found at and below the boundary. Abundances of the barbell MB reached 10⁵ cells per ml when stratification narrowed, up to 25% of total cells. The gregite producing rod was found in sulfidic waters at concentrations of order 100 cells per ml throughout the summer. It did not appear to be a gradient organism, suggesting that greigite magnetosomes can be produced in the absence of a proximal redox boundary. Our qPCR assay is the first developed for uncultivated magnetotactic bacteria in the environment. The population data obtained with this assay is important in determining the ultimate impact of MB on Fe and S cycling, as well as providing boundaries on the magnitude of their contribution to sediment magnetism via magnetosome deposition.
DE: 0424 Biosignatures and proxies
DE: 0448 Geomicrobiology
DE: 0460 Marine systems (4800)
DE: 0463 Microbe/mineral interactions
SC: Biogeosciences [B]
MN: Fall Meeting 2005