Several bacterial isolates, with an optimum growth temperature of about 50°C, were recovered from the marine hot spring at Ferraria on the island of São Miguel in the Azores. The geothermal water emerged from a porous lava flow and rapidly cooled in contact with seawater except at low tide. The bacterial species represented by strains FRR-10 T and FRR-11 was nonpigmented, strictly aerobic, and organotrophic. Several genes, bchZ, pufB, pufA, pufL, or pufM, encoding the photosynthetic reaction center proteins and the core light-harvesting complexes were not detected in these strains. The organism oxidized thiosulfate to sulfate with enhancement of growth. The organism did not require additional NaCl in the culture medium for growth, but NaCl at 1.0% enhanced growth. Phylogenetic analyses using the 16S rRNA gene sequence of strain FRR-10 T indicated that the new organism represented a new species of the ␣-3 subclass of the Proteobacteria and that it branches within the species of the genus Rhodovulum. The contradiction of classifying an organism which branches within the radiation of the genus Rhodovulum but does not possess the hallmark characteristics of this genus is discussed. However, the absence of several of these characteristics, namely, the lack of photosynthesis and pigmentation, which could be related to colonization of dark environments, and growth at high temperatures, leads to our proposal that strains FRR-10 T and FRR-11 should be classified as a new species of a novel genus, Albidovulum inexpectatum, representing, at present, the most thermophilic organism within the ␣-3 subclass of the Proteobacteria.A large number of thermophilic organisms have been isolated from continental hydrothermal areas where the levels of sodium are very low, as well as from shallow or abyssal marine hydrothermal vents where NaCl can reach the levels of seawater. Most of the organisms isolated and described from marine hydrothermal sites are slightly halophilic and have optimum growth temperatures above 70°C and some, namely Methanopyrus kandleri and Pyrolobus fumarii, have optimum temperatures for growth above 100°C (2, 20). However, many marine hot springs have lower vent temperatures and the organisms isolated from these are slightly or moderately thermophilic. These organisms do not elicit as much interest as those that grow at temperatures around 100°C, although new, slightly or moderately thermophilic species increase our perception of microbial biodiversity and may have characteristics and phylogenetic affiliations that are sometimes unexpected.We recently isolated several slightly thermophilic nonpigmented organisms from the marine hot spring at Ferraria on the island of São Miguel in the Azores that did not produce carotenoids, bacteriochlorophyll a (Bchl a), or puf genes that encode the photosynthetic reaction center proteins and the core light-harvesting complexes. These organisms were not phototrophic but they are, based on 16S rRNA gene sequence analysis, members of the genus Rhodovulum, which comprises the sp...

Page 4272, column 2, lines 34 and 35: "Hydrogen and reduced sulfur compounds are not used as energy sources" should read "Hydrogen and reduced sulfur compounds are not used as energy sources under autotrophic conditions." Line 36: "Chemoorganotrophic" should read "Facultatively chemolithoorganotrophic on reduced sulfur compounds." Line 50: "Chemoorganotrophic" should read "Facultatively chemolithoorganotrophic."