| Research Abstract |
Molecular ecological studies were done for sulfur-metabolizing microorganisms in various aquatic environments. Among these, freshwater filamentous gliding sulfide-oxidizing bacteria of the genus Thioploca were found on sediments in profundal areas of Lake Biwa, a Japanese freshwater mesotrophic lake, and characterized morphologically, ecologically and phylogenetically. The Lake Biwa Thioploca resembled morphologically Thioploca ingrica, a brackish water species from a Danish fjord. The diameter of individual trichomes was 3-5.6 μm ; the diameter of complete Thioploca filaments was in the range of 18-75 μm. Cell lengths ranged from 1.2 to 3.8 μm. In TEM specimens stained with uranyl acetate, dense intracellular particles were found, which did not show any positive signal of phosphorus and sulfur in the X-ray analysis. The 16S rRNA gene of Thioploca from Lake Biwa was amplified using newly designed Thioploca-specific primers (706-Thioploca, Biwa160F and Biwa829R) in combination with general bacterial primers, to avoid unspecific amplification of contaminating bacterial DNA. DGGE analysis of all three overlapping PCR products resulted in single DGGE bands, indicating that a single 16S rRNA gene has been amplified. With the same method, Thioploca from Lake Constance was examined. The 16S rRNA sequence was verified with FISH hybridization targeted at specific motifs of Lake Biwa Thioploca. Positive signals were obtained for the bacterial probe EUB-338, the γ-proteobacterial probe GAM42a, and the probe Biwa829 targeting Lake Biwa Thioploca. Based on the near-complete 16S rRNA sequence and on morphological similarities, Thioploca from Lake Biwa and Lake Constance are closely related to Thioploca ingrica and to each other.
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