Isolation of tellurite- and selenite-resistant bacteria from hydrothermal vents of the Juan de Fuca Ridge in the Pacific Ocean

Abstract

Deep-ocean hydrothermal-vent environments are rich in heavy metals and metalloids and present excellent sites for the isolation of metal-resistant microorganisms. Both metalloid-oxide-resistant and metalloid-oxide-reducing bacteria were found. Tellurite- and selenite-reducing strains were isolated in high numbers from ocean water near hydrothermal vents, bacterial films, and sulfide-rich rocks. Growth of these isolates in media containing K(2)TeO(3) or Na(2)SeO(3) resulted in the accumulation of metallic tellurium or selenium. The MIC of K(2)TeO(3) ranged from 1,500 to greater than 2,500 micro g/ml, and the MIC of Na(2)SeO(3) ranged from 6,000 to greater than 7,000 micro g/ml for 10 strains. Phylogenetic analysis of 4 of these 10 strains revealed that they form a branch closely related to members of the genus Pseudoalteromonas, within the gamma-3 subclass of the Proteobacteria. All 10 strains were found to be salt tolerant, pH tolerant, and thermotolerant. The metalloid resistance and morphological, physiological, and phylogenetic characteristics of newly isolated strains are described.

FIG. 1.

Plates used for the enumeration of metalloid-resistant or -reducing bacteria in bacterial-film-like formations taken from the Melarie Summit site, Main Endeavor Field. (A) Metalloid-free control plate. (B and C) Plates containing 100 μg of Na₂SeO₃ per ml and 100 μg of K₂TeO₃ per ml, respectively. The red-orange color of colonies (B) is due to the accumulation of elemental Se, and the black color (C) is due to the accumulation of elemental Te.

FIG. 2.

Strain Se-1-2-red under phase-contrast microscopy. (A) Cells grown in the absence of metalloids; (B) 48-h-old culture grown in the presence of tellurite; (C and D) 72-h-old cultures grown in the presence of selenite and tellurite, respectively. Most of the Se globules were excreted from cells and present as cell-free light-refractile particles (C), whereas most of the Te globules were located inside the cells (D).

FIG. 3.

Electron microscopy of ultrathin sections. (A) Strain Se-1-2-red grown in metalloid-free medium; (B and C) intracellular localizations of Se (B) and Te (C), as reduction products of selenite and tellurite, in strains Se-1-2-red (48-h-old culture) and Te-1-1 (72-h-old culture), respectively; (D) granules of Se released from cells of Se-1-2-red (48-h-old culture). Bars: 0.5 μm.

FIG. 4.

Unrooted tree showing the phylogenetic positions of four selected strains among members of the obligately marine genus Pseudoalteromonas, within the γ-subclass of the Proteobacteria.