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.

蓝细菌是全球饮用水和鱼类中味道和气味化合物土臭味素和2-甲基异冰片醇（2-MIB）的主要生产者。近年来，越南的Tri An和Dau Tieng水库爆发了蓝藻水华，引起人们对味道和气味问题的关注日益增加。在本研究中，在田样和Dau Tieng和Tri An水库的浮游性蓝细菌的50株分离菌株中发现了两种异味化合物Geosmin和2-MIB。首次使用顶空固相微萃取和气相色谱-质谱（HPME GC-MS）进行了筛选。产生异味化合物的能力取决于两种分子标记物：geoA和mib。结果表明，田间样品中土臭素和2-MIB的平均浓度分别为13.3到9.6 ng / L和4.9到101.7 ng / L。属于两个蓝藻属（Dolichospermum）的总共五个产生土臭素的菌株[最高浓度：湿重（ww）272.9 ng / g]和九个产生2-MIB的菌株（最高浓度：362.1 ng / g ww）。和Oscillatoria被确定。土臭素生产商中的四家还生产了2-MIB。16S rRNA最大似然（ML）树显示了代表不同形态型和基因型的分离菌株的高度多样性。BLAST搜索显示，与GenBank提供的序列相比，本研究中获得的16S rRNA基因序列的相似性值介于96.46和99.37％之间。这是越南水域中异味化合物产生蓝细菌的第一份报告。HPME GC-MS和聚合酶链反应（PCR）的结合为可靠地表征异味化合物提供了强大的工具。我们的结果表明，越南水域中属于球菌的味道和产生异味的蓝细菌尚未开发，需要进一步调查。