The marine bacterium strain MC-1 is a member of the alpha subgroup of the proteobacteria that contains the magnetotactic cocci and was the first member of this group to be cultured axenically. The magnetotactic cocci are not closely related to any other known alphaproteobacteria and are only distantly related to other magnetotactic bacteria. The genome of MC-1 contains an extensive (102 kb) magnetosome island that includes numerous genes that are conserved among all known magnetotactic bacteria, as well as some genes that are unique. Interestingly, certain genes that encode proteins considered to be important in magnetosome assembly (mamJ and mamW) are absent from the genome of MC-1. Magnetotactic cocci exhibit polar magneto-aerotaxis, and the MC-1 genome contains a relatively large number of identified chemotaxis genes. Although MC-1 is capable of both autotrophic and heterotrophic growth, it does not appear to be metabolically versatile, with heterotrophic growth confined to the utilization of acetate. Central carbon metabolism is encoded by genes for the citric acid cycle (oxidative and reductive), glycolysis, and gluconeogenesis. The genome also reveals the presence or absence of specific genes involved in the nitrogen, sulfur, iron, and phosphate metabolism of MC-1, allowing us to infer the presence or absence of specific biochemical pathways in strain MC-1. The pathways inferred from the MC-1 genome provide important information regarding central metabolism in this strain that could provide insights useful for the isolation and cultivation of new magnetotactic bacterial strains, in particular strains of other magnetotactic cocci.Almost all magnetotactic bacteria (MTB) are microaerophiles that are most abundant at the oxic-anoxic interface (OAI) of natural aquatic environments, where magnetotactic cocci are often ubiquitous and the most dominant morphotype of MTB (43). The original discovery of MTB was based on the observation of polar magnetotaxis (44) in the magnetotactic cocci (19). In addition, phylogenetic studies of the magnetotactic cocci revealed a surprising degree of diversity (104, 105) in spite of their virtually identical cell morphology of coccoid to ovoid cells that are bilophotrichously flagellated on one side of the cell (27,45,71). These organisms are phylogenetically distinct from other MTB and form a clade at the base of the alphaproteobacterial branch on the tree of life, whereas other MTB of the Alphaproteobacteria (e.g., Magnetospirillum) are nested deep within the group (106). Despite their ubiquity in natural aquatic systems, for many years only one strain of magnetotactic cocci, designated strain MC-1, was isolated and grown in pure culture (44). Recently, another related strain was isolated, but it has not yet been characterized by molecular taxonomy (70). Strain MC-1 is a marine species that was isolated from water collected from the OAI of the Pettaquamscutt Estuary (Narragansett, RI) (34). It is presently in the process of valid description as "Magnetococcus marinus."Cells of s...

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The combination of large-acceptance high-resolution X-ray optics with bright synchrotron sources permits quantitative analysis of rare events such as X-ray¯uorescence from very dilute systems, weak uorescence transitions or X-ray Raman scattering. Transition-metal K¯uorescence contains information about spin and oxidation state; examples of the characterization of the Mn oxidation states in the oxygen-evolving complex of photosystem II and Mn-consuming spores from the marine bacillus SG-1 are presented. Weaker features of the K spectrum resulting from valence-level and`interatomic' ligand to metal transitions contain detailed information on the ligandatom type, distance and orientation. Applications of this spectral region to characterize the local structure of model compounds are presented. X-ray Raman scattering (XRS) is an extremely rare event, but also represents a unique technique to obtain bulk-sensitive lowenergy (<600 eV) X-ray absorption ®ne structure (XAFS) spectra using hard ($10 keV) X-rays. A photon is inelastically scattered, losing part of its energy to promote an electron into an unoccupied level. In many cases, the cross section is proportional to that of the corresponding absorption process yielding the same X-ray absorption near-edge structure (XANES) and extended X-ray absorption ®ne structure (EXAFS) features. XRS ®nds application for systems that defy XAFS analysis at low energies, e.g. liquids or highly concentrated complex systems, reactive compounds and samples under extreme conditions (pressure, temperature). Recent results are discussed.

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