Albidovulum inexpectatum gen. nov., sp. nov., a nonphotosynthetic and slightly thermophilic bacterium from a marine hot spring that is very closely related to members of the photosynthetic genus Rhodovulum

Abstract

Several bacterial isolates, with an optimum growth temperature of about 50 degrees 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 alpha-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 alpha-3 subclass of the Proteobacteria.

FIG. 1.

Ultrastructure of strain FRR-10^T. Bar = 0.20 μm.

FIG. 2.

Agarose gel electrophoresis of PCR-amplified partial puf genes with an annealing temperature of 48°C. Lane 1, marker IV (Roche Molecular Biochemicals). Amplification products were generated with primers PUBM1 and PUBM2 from Rhodovulum sulfidophilum DNA (lane 2), Rhodovulum euryhalinum DNA (lane 4), and FRR-10^T DNA (lane 7), and with PULM1 and PULM2 from Rhodovulum sulfidophilum DNA (lane 3), Rhodovulum euryhalinum DNA (lane 5), Roseococcus thiosulfatophilus DNA (lane 6), and FRR-10^T DNA (lane 8).

FIG. 3.

Thin-layer chromatography of the polar lipids of FRR-10^T (lane 1), Rhodobacter sphaeroides (lane 2), Rhodovulum sulfidophilum (lane 3), and Rhodovulum euryhalinum (lane 4). PE, phosphatidylethanolamine; PG, phosphatidylglycerol; PC, phosphatidylcholine; SQD sulfoquinovosyldiglyceride.

FIG. 4.

Electron ionization mass spectrum of the DMOX derivative of the fatty acid with an ECL of 18.08. The interruption of the series with regularly spaced alkyl chain cleavage ions between m/z 264 and 224, together with the reduced abundance of the ion at m/z 236, identifies the compound as 11-methyl-11,12-octadecenoic acid.

FIG. 5.

Phylogenetic dendrogram based on 16S gene sequence comparisons showing the position of the FRR-10^T strain within the radiation of the species of the genus Rhodovulum.