Complete Genome Sequence of the Chemolithoautotrophic Marine Magnetotactic Coccus Strain MC-1

Abstract

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...

Comparative metagenomics of microbial communities inhabiting deep-sea hydrothermal vent chimneys with contrasting chemistries

“…Strain MC-1 has been demonstrated to use the rTCA cycle for carbon fixation, but initially no bona fide ATP citrate lyase could be identified (Williams et al, 2006). However, recently, the genome sequence of MC-1 has been completed, which has led to the suggestion that the genes Mmc13638 and Mmc13639 encode the large (aclA) and small (aclB) subunits of an ATP-dependent citrate lyase (Schubbe et al, 2009). The aclA gene of strain MC-1 contains an inserted portion that prevented its previous identification as an ATP citrate lyase.…”

Genomic insights into the uncultured genus ‘Candidatus Magnetobacterium’ in the phylum Nitrospirae

“…Although this is a conservative estimate because the genome of Mcas is not complete, the products of these orthologous genes seem to be common in Nitrospirae and Proteobacteria MTB, and hence some of them may have roles in magnetotaxis or magnetosome formation. It is widely accepted that chemotaxis and motility have important roles in the magnetotactic swimming behaviors of MTB (Matsunaga et al, 2005;Schü bbe et al, 2009), and genes involved in these processes are among the shared orthologous genes identified (Supplementary Table S3). …”

“…In addition to the magnetosome genes, we have compared the draft genome of Mcas with four complete genomes of Proteobacteria MTB strains, including M. magneticum AMB-1 (Matsunaga et al, 2005), M. gryphiswaldense MSR-1 (Wang et al, 2014) and M. marinus MC-1 (Schü bbe et al, 2009) belonging to the Alphaproteobacteria and D. magneticus RS-1 (Nakazawa et al, 2009) Table S3). Although this is a conservative estimate because the genome of Mcas is not complete, the products of these orthologous genes seem to be common in Nitrospirae and Proteobacteria MTB, and hence some of them may have roles in magnetotaxis or magnetosome formation.…”

Magneto-aerotactic bacteria deliver drug-containing nanoliposomes to tumour hypoxic regions

“…Furthermore, such an approach could also benefit from the fact that bacteria-mediated delivery of nanoparticles and cargo into cells for various applications is already feasible 24 . Besides potential future efforts towards genetically modified carriers 25 based on known genome sequences 26 and the development of better magnetotactic guidance algorithms to increase the therapeutic index further, these initial findings may influence not only specific engineering concepts and medical interventional methods, but also open opportunities for the synthesis of new targeted therapeutic, imaging, and diagnostic vectors while providing further opportunities to enhance the delivery and efficacy of existing nanocarriers.…”