Dynamics and polyphasic characterization of odor-producing cyanobacterium Tychonema bourrellyi from Lake Erhai, China.

The previous studies indicated that Tychonema-like strains from Lake Erhai could release geosmin so that the species was listed as the potential harmful cyanobacteria influencing the drinking water safety around Lake Erhai. But, the dynamics and biological information of this species were too limited. In this study, the polyphasic approach was used to reveal its biological characterization and the dynamics in Lake Erhai. The characters of trichomes, including filaments with solitary or bundle state, reddish-brown or blue-green color, planktonic habitat, and presence of keritomized content, were examined by the microscopic method. The 16S rDNA sequences of these strains were used for phylogenetic analysis and molecular identification. The strains were morphologically classified as Tychonema bourrellyi, and geosmin and β-ionone were identified as the major volatile substances using gas chromatography-mass spectrometry (GC-MS) analysis. No strains of T. bourrellyi were found to produce microcystin by the HPLC and mcy gene approaches. Cell numbers at 12 sampling sites in Lake Erhai were shown as an average of 3 × 10(4) cells L(-1) in 2009 and 2010. The obvious peaks occurred in July and August each year. This was the first report on occurrence of T. bourrellyi from outside of Europe, and T. bourrellyi was also a newly recorded species in China. Such a result demonstrated that T. bourrellyi could distribute extending from cold waters in North Europe to the warm waters in subtropical regions. It was interesting to observe the coincidence of the occurrence of T. bourrellyi with slightly eutrophicated waters since Lake Erhai had been regarded as an early phase of eutrophicated lake.