Filamentous sulfur-oxidizing bacteria of the genus Thioploca from Lake Tonle Sap in Cambodia

Abstract

Members of the genus Thioploca are uncultured filamentous sulfur-oxidizing bacteria that live in freshwater/brackish sediments and have the ability to store nitrate in high concentrations in their cells. Their close relatives that inhabit marine sediments, such as Thiomargarita and 'Candidatus Marithioploca', are thought to greatly influence cycles of sulfur, nitrogen, and phosphorus. To date, the genus Thioploca has been reported only from temperate and subarctic areas. Our demonstration of Thioploca in Lake Tonle Sap, Cambodia, is the first report of this genus in a tropical lake. The filaments obtained from Lake Tonle Sap were morphologically similar to those of other lakes. Phylogenetic analysis based on genes for 16S rRNA, 23S rRNA, and the 16S-23S rRNA internal transcribed spacer (ITS) region revealed that 3 distinct lineages coexist in this lake. These results indicate that the geographical distribution and phylogenetic diversity of the genus Thioploca is greater than previously thought.KEY WORDS: Sulfur-oxidizing bacteria · Freshwater lake · Sediment · Phylogeny Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 66: [295][296][297][298][299][300] 2012 (Lauter born 1907). Subsequently, populations were reported from Lake Erie and Lake Ontario in North America (Maier & Murray 1965, Dermott & Legner 2002, Lake Baikal in Siberia (Zemskaya et al. 2001), and Lake Biwa, Lake Ogawara, and Lake Okotanpe in Japan (Nishino et al. 1998, Kojima et al. 2006, Nemoto et al. 2011. These lakes are located in areas of mid-range to high latitudes in the northern hemisphere. The 16S rRNA gene sequences of Thioploca in these lakes are very closely related, even though they are separated geographically.In the present study, we report the occurrence of the genus Thioploca in Lake Tonle Sap (Cambodia), which is located in a tropical monsoon climatic zone, and show results of phylogenetic analyses. MATERIALS AND METHODS Samples were obtained in May 2005, from the south basin of Lake Tonle Sap. This lake is characterized by a dramatic seasonal change of water level, and the samples were obtained in the season of shallow water depth. The sampling site, Site S3 (12°33' 57'' N, 104°22' 10'' E; 0.4 m deep), corresponds to the site of a previous study (Ohtaka et al. 2010). At the sampling time, the pH and specific conductivity of surface water were 8.0 and 155 µS cm −1 respectively (Ohtaka et al. 2010). The lake water was characterized by very low transparency (0.02 m). The sediment samples, taken using an Ekman-Birge grab sampler, were passed through a mesh with a pore size of 0.25 mm. The retained filamentous materials were immediately fixed in 100% ethanol.Before microscopic observation, the filamentous samples were soaked in distilled water for 30 min to replace the ethanol with water. The shapes of the filaments were observed, and the diameters of 200 trichomes were measured under an optical microscope (Axioplan 2, Zeiss).Thioploca filaments (sheaths with trichomes) were c...

Ecophysiology of Thioploca ingrica as revealed by the complete genome sequence supplemented with proteomic evidence

“…Morphologically, T. ingrica was defined as a Thioploca species having a trichome 2.0-4.5 mm in diameter (Wislouch, 1912;Maier, 1984). Organisms that fit this description have been found in freshwater and brackish sediments of various localities, and the placement of these organisms in the same species has been generally supported by their 16S rRNA gene sequences (Maier and Murray, 1965;Nishino et al, 1998;Zemskaya et al, 2001Zemskaya et al, , 2009Dermott and Legner, 2002;Kojima et al, 2003Kojima et al, , 2006Høgslund et al, 2010;Nemoto et al, 2011Nemoto et al, , 2012Salman et al, 2011). Nitrate accumulation by T. ingrica was reported in previous studies, although the intracellular concentrations were much lower than in relatives with large vacuoles (Zemskaya et al, 2001;Kojima et al, 2007;Høgslund et al, 2010).…”