Genome sequence of the deep-sea gamma-proteobacterium Idiomarina loihiensis reveals amino acid fermentation as a source of carbon and energy.

We report the complete genome sequence of the deep-sea gamma-proteobacterium, Idiomarina loihiensis, isolated recently from a hydrothermal vent at 1,300-m depth on the Loihi submarine volcano, Hawaii. The I. loihiensis genome comprises a single chromosome of 2,839,318 base pairs, encoding 2,640 proteins, four rRNA operons, and 56 tRNA genes. A comparison of I. loihiensis to the genomes of other gamma-proteobacteria reveals abundance of amino acid transport and degradation enzymes, but a loss of sugar transport systems and certain enzymes of sugar metabolism. This finding suggests that I. loihiensis relies primarily on amino acid catabolism, rather than on sugar fermentation, for carbon and energy. Enzymes for biosynthesis of purines, pyrimidines, the majority of amino acids, and coenzymes are encoded in the genome, but biosynthetic pathways for Leu, Ile, Val, Thr, and Met are incomplete. Auxotrophy for Val and Thr was confirmed by in vivo experiments. The I. loihiensis genome contains a cluster of 32 genes encoding enzymes for exopolysaccharide and capsular polysaccharide synthesis. It also encodes diverse peptidases, a variety of peptide and amino acid uptake systems, and versatile signal transduction machinery. We propose that the source of amino acids for I. loihiensis growth are the proteinaceous particles present in the deep sea hydrothermal vent waters. I. loihiensis would colonize these particles by using the secreted exopolysaccharide, digest these proteins, and metabolize the resulting peptides and amino acids. In summary, the I. loihiensis genome reveals an integrated mechanism of metabolic adaptation to the constantly changing deep-sea hydrothermal ecosystem.

Idiomarina loihiensis sp. nov., a halophilic gamma-Proteobacterium from the Lo'ihi submarine volcano, Hawai'i.

During an investigation of bacterial diversity at hydrothermal vents on the Lo'ihi Seamount, Hawai'i, a novel bacterium (designated L2-TR(T)) was cultivated, which shares 99.9 % 16S rRNA gene sequence similarity over 1415 nt with an uncultured eubacterium from sediment at a depth of 11 000 m in the Mariana Trench. The nearest cultivated neighbour of L2-TR(T), however, is Idiomarina abyssalis KMM 227(T), with which it shares 98.9 % 16S rRNA sequence similarity. L2-TR(T) differed from I. abyssalis KMM 227(T) in several phenotypic respects, including growth at 46 degrees C and in medium that contained 20 % (w/v) NaCl. DNA-DNA hybridization data showed that L2-TR(T) did not belong to the species I. abyssalis (43.4 % DNA-DNA reassociation). Cells of L2-TR(T) were Gram-negative rods, 0.35 microm wide and 0.7-1.0 microm long, which were occasionally up to 1.8 microm in length. Cells were motile by a single polar or subpolar flagellum. The major fatty acid in L2-TR(T) was iso-C(15 : 0) (32.6 %). The DNA G+C content was 47.4 mol%. Phenotypic and genotypic analyses indicated that L2-TR(T) could be assigned to the genus Idiomarina but, based on significant phenotypic and genotypic differences, constituted a novel species within this genus, Idiomarina loihiensis sp. nov., of which L2-TR(T) (=ATCC BAA-735(T)=DSM 15497(T)) is the type strain.

Microbial community in acidic hydrothermal waters of volcanically active White Island, New Zealand.

We report the first description of the microbial community in a stream of acidic hydrothermal waters on volcanically active White Island, New Zealand, using both molecular and microbiological methods. alpha- and beta-Proteobacteria, green-sulfur bacteria, and uncultured Firmicutes were identified from the community DNA-based 16s rRNA gene library. The same bacterial groups and the Rhodophyte Cyanidium caldarium were represented in enrichment cultures. C. caldarium, two Firmicutes and an acidophilic alpha-Proteobacterium, Acidiphilium cryptum, were brought into pure culture. Bacteria cultured from the stream grow at pH > or =2, and the Cyanidium grows at pH 0.2.