OCCURRENCE OF PLANKTONIC CYANOBACTERIUM TYCHONEMA BOUURRELLYI IN ERHAI LAKE AND ITS TAXONOMIC STUDIES

Tychonema was separated from Oscillatora and established as a new genus in 1988 by setting Tychonema tenue as the type species. This new genus was accepted and currently considered to include three species as T. tenue, T. bornetii and T. bourrellyi. T. bornetii was described from the Tibet Plateau, but no reports on type species and its related taxa of Tychonema were from China. The present study reported the occurrence of a Tychonemaspecies from the Erhai Lake, and this species was morphologically identified as T. bouurrellyi based on its planktonic habit, trichome color and cellular content structure etc. Cultivated strains were also isolated, and comparative analyses on the sequences of 16S rDNA also confirmed that the T. bouurrellyi strain was tightly grouped with the strains of T. bouurrellyi/T. tenue. This is the first report on occurrence of T. bouurrellyi from outside of Europe, and T. bouurrellyi is also a newly recorded species in China. Such a result demonstrated that T. bouurrellyi can distribute extending from cold waters in North Europe to the warm waters in subtropical regions. It is interesting to coincide the occurrence of T. bouurrellyi with slightly eutrophicated waters since Lake Erhai has been regarded as an early phase of eutrophicated lake. The taxonomic problem and revision of the Tychonema genus was discussed in this study.