In Lake Shinji, Japan, periodic outbreaks of musty odour have occurred since mid-May 2007. Although the substance responsible for the odour was identified as geosmin, the odour-producing organism was unknown. We cultivated an axenic unialgal strain and determined that a species of Coelosphaerium (Synechococcales) was responsible for the production of geosmin in Lake Shinji. Our analysis was conducted using gas chromatography/mass spectrometry to determine the odorous compound. To determine the algae species, it was observed by optical microscopy to describe its morphological characteristics and the polymerase chain reaction was used to characterise the nucleotide sequence of the 16S rRNA gene and the 16S-23S rRNA internal transcribed spacer region. In addition, we explored the relationship between the number of cells of the Coelosphaerium sp. and the concentration of geosmin. In conclusion, geosmin, the cause of the musty odour in Lake Shinji in autumn 2009, was produced by Coelosphaerium sp., and to our knowledge, this is the first report of a geosmin-producing species in the family Coelosphaeriaceae.
close to the theoretical value for both compounds, and almost all organic carbons in each solution were detectable by TOC equipment. On the other hand, the COD oxidation rate in both the saccharide and amino acid solutions decreased according to the increase in the solutions' concentration, and there were also significant differences in the decomposition rate in each compound. The relationship between field data on COD and TOC in Shinji and Nakaumi lakes may be approximated by a quadratic expression, but the approximated curve did not pass the original point.This result indicates that there are some organic compounds that can be decomposed by TOC equipment but not by COD analytical methods, and the decomposition of COD was insufficient in high concentrations in environmental water. Therefore, we consider COD not to be an appropriate indicator of the organic compounds in public waters;instead, TOC should be used.
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