High incidence of halotolerant bacteria in Pacific hydrothermal-vent and pelagic environments.

The abundance of halotolerant microorganisms in hydrothermal-vent and pelagic waters in the North and South Pacific was estimated by the most probable number (MPN) technique using a heterotrophic 16% NaCl medium incubated at 20-24 degrees C. Based on these MPNs and direct counts with epifluorescence microscopy to enumerate the total microbial population, salt-tolerant microbes comprised from <0.01 to >28% of the total microbial community. Fourteen isolates from these MPN enrichments were identified by sequencing a portion of the 16S rRNA gene, and all were found to belong to the genera Halomonas and Marinobacter. The response to salt of mesophilic hydrothermal-vent microbial isolates obtained without selecting for salt tolerance was also examined. Forty-one of 65 strains cultured from hydrothermal plume waters, low-temperature hydrothermal fluids, sulfide rock and an animal specimen at approximately 2000-2200 m depth from the Endeavour Segment of the Juan de Fuca Ridge were subjected to increasing concentrations of NaCl, and over half grew at a NaCl concentration that is lethal to many commonly isolated marine bacteria. At least 36 of the 65 isolates (>/=55%) grew in the enrichment medium supplemented with 10% NaCl; at least 30 of 65 (>/=46%) grew with 16% NaCl; at least 20 of 65 (>/=31%) tolerated 22% NaCl. Based on phylogenetic analysis of the 16S rRNA gene in nine of these 65 isolates, four belonged to the genus Halomonas. These Halomonas strains tolerated 22-27% NaCl. It is possible that a majority of the other 16 isolates which grew with 22% NaCl are also Halomonas based on their degree of halotolerance, morphology, and apparent abundance as revealed by MPN enrichments. The four Halomonas strains obtained without selecting for halotolerance were further characterized physiologically and metabolically. Overall, they grew between -1 degrees C and 40 degrees C, were facultative aerobes, oxidized between 49 and 70 organic compounds according to Biolog plate substrate utilization matrices, grew with oligotrophic quantities of carbon (0.002% yeast extract) in liquid media, reduced nitrate to nitrite, and tolerated up to 0.05-3 mM Cd(2+). Halomonas is one of the most abundant culturable organisms in the ocean, and its success may be attributed to its metabolic and physiological versatility.

Archaeaplankton in the Columbia River, its estuary and the adjacent coastal ocean, USA.

PCR-amplified 16S rRNA genes from particle-attached and free-living Archaea in the Columbia River estuary, particle-attached Archaea in the river, and Archaea in the adjacent coastal ocean were cloned, and 43 partial sequences were determined. There was a high diversity of Archaea in the estuary, especially among the particle-attached Archaea, with representatives from four major phylogenetic clusters. Eighteen of 21 estuarine clones were closely related to clones from the river and the coastal ocean or to clusters of marine and soil clones identified in other studies. This contrasts with a similar study of the estuarine bacterial community that found 62% of bacterial 16S rRNA clones to be unique to the estuary. Archaea in the estuary were primarily allochthonous, and therefore, unlike the bacteria, probably do not form a native estuarine community.

The Quantum Event of Oceanic Crustal Accretion: Impacts of Diking at Mid-Ocean Ridges

Seafloor diking-eruptive events represent the irreducible, quantum events of upper oceanic crustal accretion. They record events by which a large portion of the oceanic crust has formed through geological history. Since 1993, the U.S. Navy's real-time Sound Surveillance System has allowed location of ongoing acoustic signatures of dike emplacement and basalt eruptions at ridge crests in the northeast Pacific. These diking-eruptive events trigger a sequence of related, rapidly evolving physical, chemical, and biological processes. Magmatic volatiles released during these events may provide nutrients for communities of subseafloor microorganisms, some of which thrive in high-temperature anaerobic environments. Many of the organisms identified from these systems are Archaea. If microorganisms can thrive in the water-saturated pores and cracks within deep, volcanically active portions of our planet, other hydrothermally active planets may harbor similar life forms.