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Abstract
An isolate of purple non-sulfur bacteria was obtained from an acidic Sphagnum peat bog and designated strain RST. The colour of cell suspensions of this bacterium growing in the light under anaerobic conditions is purplish red. Cells of strain RST are rod-shaped, 0.8–1.0 μm wide and 2.0–6.0 μm long, motile by means of polar flagella, reproduce by budding and have a tendency to form rosette-like clusters in older cultures. The cells contain lamellar intracytoplasmic membranes underlying, and parallel to, the cytoplasmic membrane. The photosynthetic pigments are bacteriochlorophyll a and carotenoids; the absorption spectrum of living cells shows maxima at 377, 463, 492, 527, 592, 806 and 867 nm. The cells grow photoheterotrophically under anaerobic or microaerobic conditions with various organic carbon sources or grow photolithoautotrophically with H2 and CO2. Strain RST is a moderately acidophilic organism exhibiting growth at pH values between 4.8 and 7.0 (with an optimum at pH 5.2–5.5). The major fatty acids are 16 : 1ω7c and 18 : 1ω7c; the major quinones are Q-10 and Q-9. The DNA G+C content of strain RST is 62.6 mol%. Analysis of the 16S rRNA gene sequence revealed that the novel isolate is most closely related (97.3 % sequence similarity) to the type strain ATCC 25092T of the moderately acidophilic purple non-sulfur bacterium Rhodoblastus acidophilus, formerly named Rhodopseudomonas acidophila. However, in contrast to Rbl. acidophilus, strain RST is not capable of aerobic growth in the dark, has no spirilloxanthin among the carotenoids and differs in the pattern of substrate utilization. The value for DNA–DNA hybridization between strain RST and Rbl. acidophilus ATCC 25092T is only 22 %. Thus, strain RST represents a novel species of the genus Rhodoblastus, for which the name Rhodoblastus sphagnicola sp. nov. is proposed. Strain RST (=DSM 16996T=VKM B-2361T) is the type strain.
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