Prismatic magnetite magnetosomes from cultivated Magnetovibrio blakemorei strain MV-1: a magnetic fingerprint in marine sediments? Luigi Jovane, 1 * Fabio Florindo, 2 Dennis A. Bazylinski 3 and Ulysses Lins 4 1 Instituto Oceanográfico, Universidade de São Paulo, São Paulo, Brazil. 2 Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy. 3 School of Life Sciences, University of Nevada at Las Vegas, Las Vegas, Nevada, USA. 4 Instituto de Microbiologia, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil. Summary The magnetic properties (first-order reversal curves, ferromagnetic resonance and decomposition of satu- ration remanent magnetization acquisition) of Magne- tovibrio blakemorei, a cultivated marine magnetotactic bacterium, differ from those of other magnetotactic species from sediments deposited in lakes and marine habitats previously studied. This finding suggests that magnetite produced by some magnetotactic bacteria retains magnetic properties in relation to the crystal- lographic structure of the magnetic phase produced and thus might represent a ‘magnetic fingerprint’ for a specific magnetotactic bacterium. The use of this fin- gerprint is a non-destructive, new technology that might allow for the identification and presence of spe- cific species or types of magnetotactic bacteria in certain environments such as sediments. Introduction Magnetotactic bacteria are prokaryotic microorganisms which internally biomineralize magnetite (Fe 3O4) or greigite (Fe3S4) crystals (nanoparticles) or both enveloped in a lipid bilayer membrane. These organelles, called magneto- somes, contribute significantly to the magnetic properties of sediments (Bazylinski and Frankel, 2004). Magneto- somes have very interesting biotechnological chara- cteristics because they are made of singular, perfect, single-magnetic-domain (SD) crystals of magnetite or greigite that are usually aligned in chains within the cell (Schüler, 2006). Here we present the results of a study using Magne- tovibrio blakemorei strain MV-1: a cultivated magnetotac- tic marine vibrio that produces prismatic magnetite magnetosomes (~50–100 nm diameter) and was origi- nally isolated from sediment collected from a salt marsh pool near the Neponset River (Milton, MA, USA) (Bazy- linski et al., 1988; 2012). In this report, we focus on the magnetosome magnetite crystals of M. blakemorei and their importance in future studies of sediments and their environmental significance in oceanographic changes. Because M. blakemorei lives naturally in the sediment and water column and produces pseudo-hexagonal pris- matic magnetite magnetosomes under microaerobic and strictly anaerobic conditions, its magnetosome crystals may provide a magnetic fingerprint of anaerobic condi- tions that can be identified in the geological record. The presence of magnetotactic bacteria in sediments, detected as magnetosome crystals, namely magnetofos- sils, may be the primary source of natural remanence in these sediments and is able to maintain the non- interacting SD bulk magnetic properties because of the preservation of the chain structure (Moskowitz et al., 1993). Recently, their presence has been associated to hyperthermal events and high-productivity climatic events (Schumann et al., 2008; Roberts et al., 2011; Chang et al., 2012) outlining the importance of magnetotactic bacteria as a proxy for reconstructing paleoenvironments. Magnetic analyses provide a quick and efficient tool to determine the presence of magnetotactic bacteria and/or magnetosome crystals in recent or ancient sediments or in the water columns of aquatic habitats (Roberts et al., 2011; 2012). In particular, first-order reversal curves (FORC) (Roberts et al., 2000; Egli et al., 2010), ferromag- netic resonance (FMR) measurements (e.g. Weiss et al., 2004) and decomposition of saturation remanent mag- netization (M r) acquisition (DAM) (Heslop et al., 2002) are well-understood, rapid, inexpensive and non-destructive measurements which can be used to determine magnetic properties, magnetic grain-size distributions, interactions and crystallographic anomalies. FORC diagrams are contour plots of the second derivative of magnetic fields Hu and Hc, which are related to the coercivity (Hu) and bias Received 7 June, 2012; revised 19 September, 2012; accepted 23 September, 2012. *For correspondence. E-mail jovane@usp.br; Tel. (+55) 11 31096609; Fax (+55) 11 31096610. Environmental Microbiology Reports (2012) 4(6), 664–668 doi:10.1111/1758-2229.12000 © 2012 Society for Applied Microbiology and Blackwell Publishing Ltd