Summary auto-generated
Researchers isolated and characterized a new thermophilic bacterium, Porphyrobacter tepidarius strain OT3T, from a brackish hot spring in Japan. This obligately aerobic bacterium synthesizes bacteriochlorophyll a and possesses a photosynthetic apparatus with light-harvesting and reaction center complexes, yet cannot grow anaerobically in light. The strain is the first thermophilic aerobic photosynthetic bacterium discovered, with optimal growth between 40-48°C and capability to grow up to 50°C, significantly exceeding the 25-30°C optimum of previously described aerobic photosynthetic bacteria. Cells are nonmotile, ovoid to short rods without flagella or intracytoplasmic membranes. Phylogenetic analysis based on 16S rRNA sequences places the bacterium within the α-4 group of Proteobacteria, most closely related to Porphyrobacter neustonensis (96.8% sequence similarity). The organism utilizes glucose, acetate, glutamate, butyrate, Casamino acids, and yeast extract as energy sources. Its pigmentation includes bacteriochlorophyll a, carotenoid sulfates, nostoxanthin, and bacteriorubixanthinal. The DNA G+C content is 65.0 mol%, similar to other freshwater members of the α-4 group.
Key findings
- P. tepidarius is the first thermophilic aerobic photosynthetic bacterium, with optimal growth at 40-48°C, compared to 25-30°C for other aerobic photosynthetic bacteria
- The organism contains bacteriochlorophyll a and functional photosynthetic reaction centers but grows only under aerobic conditions in the dark, not anaerobically in light
- 16S rRNA sequence analysis confirms the bacterium belongs to the α-4 group of Proteobacteria, with closest relationship to P. neustonensis at 96.8% similarity
- The bacterium is nonmotile with ovoid-to-short rod morphology, lacks intracytoplasmic membranes, and utilizes limited organic substrates including glucose, acetate, and glutamate
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Abstract
A new thermophilic bacterium, strain OT3T (T = type strain), was isolated from a brackish hot spring. Strain OT3T is an obligate aerobe that synthesizes bacteriochlorophyll a and has a photosynthetic apparatus. This isolate is a thermophilic bacterium with an optimal growth temperature of 40 to 48°C. The cells are nonmotile, ovoid to short rods. An analysis of 16S rRNA sequences revealed that the new strain forms a coherent cluster with members of the α-4 group of the α subclass of the Proteobacteria, which contains the genera Erythrobacter, Erythromicrobium, and Porphyrobacter. The closest relative is Porphyrobacter neustonensis with a 16S rRNA sequence similarity of 96.8%. The in vivo absorption spectrum has maxima at 460, 494, 596, 800, and 870 nm. The main carotenoids are OH-β-carotene sulfate derivatives, nostoxanthin, and bacteriorubixanthinal. Growth occurs with glucose, acetate, glutamate, butyrate, Casamino Acids, and yeast extract as sole energy sources. The pigment composition and nutritional profile of the new isolate are similar to the pigment composition and nutritional profile of P. neustonensis. Although there are marked differences in cell morphology between the new isolate and the budding bacterium P. neustonensis, the results of phenotypic and genetic comparisons suggest that the new isolate is closely related to P. neustonensis. Consequently, we assign the new isolate to the genus Porphyrobacter and propose the name Porphyrobacter tepidarius sp. nov. for it; the type strain of P. tepidarius is strain OT3 (= DSM 10595).