Teredinibacter turnerae T7901

Teredinibacter turnerae (strain ATCC 39867 / T7901) is a cellulolytic and diazotrophic Gram-negative bacterium isolated from the gills of woodboring marine bivalves Bankia gouldi of the family Teredinidae (shipworms). This species are shown to coexist with other as yet uncultivated bacteria as a component of an intracellular endosymbiotic bacterial consortium within specialized cells (bacteriocytes) of the gill epithelium. It displays an unusual combination of properties, being the only aerobic bacterium known to grow with cellulose and dinitrogen, respectively, as its sole carbon and nitrogen sources. The cellulolytic and diazotrophic capabilities of T. turnerae suggested two potential roles for this bacterium in the shipworm symbiosis. The first is to produce enzymes that may assist the host in degrading carbohydrate components of woody plant materials (cellulose, hemicellulose, and pectin). Shipworms are the only marine animals known to grow and reproduce normally with wood as their sole source of particulate food. The second is to provide a source of fixed nitrogen to supplement the host's nitrogen deficient diet of wood. T. turnerae genome is notable for containing an unusually large number of protein domains involved in the degradation of complex polysaccharides, including glycoside hydrolases (GH), carbohydrate esterases (CE), pectin lyases (PL), and carbohydrate binding modules (CBM). However, in contrast to S. degradans, which is a generalist capable of degrading more than 10 types of plant, algal, animal and fungal polysaccharides, the T. turnerae genome lacks enzyme systems for degradation of common marine polysaccharides including agar, alginate, and fucoidan and has only comparatively sparse representation of chitinase (two vs. seven in S. degradans) and laminarinase (six vs. ten in S. degradans) genes. Enzymes for degradation of the fungal polysaccharide pullulan are also absent in T. turnerae. Instead, the gene content of the T. turnerae genome suggests a high degree of specialization for degrading polysaccharides associated with woody plant materials, including cellulose, xylan, mannan, galactorhamnan and pectin. The genome of T. turnerae revealed a complete set of nitrogen fixation genes (nif) organized in three main clusters. The first cluster contains nitrogenase accessory and regulatory genes including nifQ, nifBAL, and the electron transport complex genes rnfABCDGE. The second cluster contains the structural nitrogenase genes encoded by the nifHDKT operon. The third cluster contains genes nifENX whose gene products function to synthesize nitrogenase molydenum-iron cofactors, as well as nifUSVPWZM whose gene products also function in nitrogen fixation. In addition to genes involved in nitrogen fixation, about 40 genes in the genome of T. turnerae are predicted to function in nitrogen assimilation. The majority of these are dedicated to urea metabolism and transport. The genome of T. turnerae is also of interest as an example of the range of adaptations associated with intracellular endosymbionts of eukaryotes. A characteristic suite of genomic modifications, including reduced genome size, skewed %G+C, elevated mutation rates and loss of genes of core metabolism, are identified through analysis of genomes of a number of obligate intracellular symbionts. However, this is not the case for T. turnerae, which stands as an example of a bacterium that is observed in nature only as an endosymbiont, but that can be cultivated in vitro in a simple defined medium without added vitamins or growth factors. (Adaptated from PMID:19568419). (HAMAP: TERTT)