In March 1996, a survey of hydrothermal sites on the island of Montserrat was carried out. Six sites (Galway's Soufriere, Gages Upper and Lower Soufrieres, Hot Water Pond, Hot River, and Tar River Soufriere) were mapped and sampled for chemical, ATP, and microbial analyses. The hydrothermal Soufriere sites on the slopes of the active Chances Peak volcano exhibited temperatures up to almost 100 degreesC and were generally either mildly acidic at pH 5-7 or strongly acidic at pH 1.5-3, but with some hot streams and pools of low redox potential at pH 7-8. Hot Water Pond sites, comprising a series of heated pools near the western shoreline of the island, were neutral and saline, consistent with subsurface heating of entrained seawater. Biological activity shown by ATP analyses was greatest in near-neutral pH samples and generally decreased as acidity increased. A variety of heterotrophic and chemolithotrophic thermophilic organisms were isolated or observed in enrichment cultures. Most of the bacteria that were obtained in pure culture were familiar acidophiles and neutrophiles, but novel, iron-oxidizing species of Sulfobacillus were revealed. These species included the first mesophilic iron-oxidizing Sulfobacillus strains to be isolated and a strain with a higher maximum growth temperature (65 degreesC) than the previously described moderately thermophilic Sulfobacillus species
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