Abstract
Cyanobacteria are the major producers of the taste and odour compounds geosmin and 2-methylisoborneol (2-MIB) in drinking water and fish worldwide. In recent years, the outbreaks of cyanobacteria blooms in Tri An and Dau Tieng Reservoirs, Vietnam have led to an increase attention in taste and odour problems. In the present study, the two off-flavour compounds geosmin and 2-MIB were found in field samples and 50 isolated strains of planktonic cyanobacteria from Dau Tieng and Tri An Reservoirs. They were screened for the first time using headspace solid-phase microextraction and gas chromatography–mass spectrometry (HPME GC–MS). The ability to produce off-flavour compounds was determined by the presence of two molecular markers: geoA and mib. Results showed that mean geosmin and 2-MIB concentrations ranged from 13.3 to 9.6 ng/L and 4.9 to 101.7 ng/L in field samples, respectively. A total of five geosmin-producing strains [with the highest concentration: 272.9 ng/g wet weight (ww)] and nine 2-MIB-producing strains (with the highest concentration: 362.1 ng/g ww) belonging to two cyanobacteria genera Dolichospermum and Oscillatoria were identified. Four of the geosmin producers also produced 2-MIB. The 16S rRNA maximum likelihood (ML) tree showed a high diversity of the isolated strains that represented different morphotypes and genotypes. The BLAST searches revealed that the 16S rRNA gene sequence obtained in this study shared the similarity values ranging between 96.46 and 99.37% compared to the available sequences from GenBank. This is the first report of off-flavour compound producing cyanobacteria in Vietnamese waters. The combination of HPME GC–MS and polymerase chain reaction (PCR) provides a robust tool for reliably characterizing the off-flavour compound. Our results highlight that taste and odour-producing cyanobacteria belonging to Chroococcales in Vietnamese waters are unexplored and require further investigation.
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