Extremely barophilic bacteria isolated from the Mariana Trench, Challenger Deep, at a depth of 11,000 meters

Abstract

Two strains of obligately barophilic bacteria were isolated from a sample of the world's deepest sediment, which was obtained by the unmanned deep-sea submersible Kaiko in the Mariana Trench, Challenger Deep, at a depth of 10,898 m. From the results of phylogenetic analysis based on 16S rRNA gene sequences, DNA-DNA relatedness study, and analysis of fatty acid composition, the first strain (DB21MT-2) appears to be most highly similar to Shewanella benthica and close relatives, and the second strain (DB21MT-5) appears to be closely related to the genus Moritella. The optimal pressure conditions for growth of these isolates were 70 MPa for strain DB21MT-2 and 80 MPa for strain DB21MT-5, and no growth was detected at pressures of less than 50 MPa with either strain. This is the first evidence of the existence of an extreme-barophile bacterium of the genus Moritella isolated from the deep-sea environment.

FIG. 1

PCR amplification of pressure-regulated operons ORF1.2 and ORF3 from the DNAs of Mariana isolates by using the ORF1.2 and ORF3 primers. Lanes: 1 and 14, DNA size marker DRIgestIII (λHindIII plus φX174 HaeIII; Pharmacia Biotech, Uppsala, Sweden); 2 and 8, DB21MT-2; 3 and 9, DB21MT-4; 4 and 10, DB21MT-5; 5 and 11, DB21MT-6; 6 and 12, DB21MT-9; and 7 and 13, DB21MT-9.

FIG. 2

Electron micrographs (negative staining) of extreme-barophile bacteria (strains DB21MT-2 [A] and DB21MT-5 [B]). Bar, 1 μm.

FIG. 3

Growth properties of the extreme barophiles at elevated hydrostatic pressure. Dotted line, DB21MT-2; solid line, DB21MT-5. t_d, doubling time (in hours).

FIG. 4

Phylogenetic tree showing the relationships among the isolated bacteria within the γ subdivision of the class Proteobacteria. The scale represents the average numbers of nucleotide substitutions per site. Bootstrap values are shown for frequencies per 1,000 times.