Cyanobacteria can exist in water resources and produce odorants. 2-Methylisoborneol (2-MIB) and geosmin are the main odorant compounds affecting the drinking water quality in reservoirs. In this study, encoding genes 2-MIB (mic, monoterpene cyclase) and geosmin (geo, putative geosmin synthase) were investigated using newly developed primers for quantitative PCR (qPCR). Gene copy numbers were compared to 2-MIB/geosmin concentrations and cyanobacterial cell abundance. Samples were collected between July and October 2020, from four drinking water sites in South Korea. The results showed similar trends in three parameters, although the changes in the 2-MIB/geosmin concentrations followed the changes in the mic/geo copy numbers more closely than the cyanobacterial cell abundances. The number of odorant gene copies decreased from upstream to downstream. Regression analysis revealed a strong positive linear correlation between gene copy number and odorant concentration for mic (R² = 0.8478) and geo (R² = 0.601). In the analysis of several environmental parameters, only water temperature was positively correlated with both mic and geo. Our results demonstrated the feasibility of monitoring 2-MIB/geosmin occurrence using qPCR of their respective synthase genes. Odorant-producing, gene-based qPCR monitoring studies may contribute to improving drinking water quality management.

Summary: We investigated the abundance of Pseudanabaena species and the concentration of the monoterpene 2‐methylisoborneol (2‐MIB) from July to October at three sampling sites in South Korea. To identify the main cause of 2‐MIB occurrence in drinking water source, we characterized and performed a phylogenetic analysis of the 2‐MIB synthase gene. Pseudanabaena was the dominant cyanobacterium (68%–100%) among the samples. At all three sampling sites, a strong positive correlation was detected between 2‐MIB concentrations and Pseudanabaena cell numbers. A phylogenetic analysis of 222 MIB sequences isolated from the water samples showed that all of the clones were affiliated with the Pseudanabaena MIB synthase gene, demonstrating that the 2‐MIB in the Han River drinking water source was produced by Pseudanabaena sp. Using a clone of the 2‐MIB gene, network‐based analysis and unweighted pair group method with arithmetic mean analysis were used to examine temporal and spatial variation in the 2‐MIB concentration and Pseudanabaena abundance. The network analysis showed greater temporal than spatial similarity among the 2‐MIB gene clones. Together, our results demonstrate that Pseudanabaena was the main producer of 2‐MIB. These findings provide important information for odour management in drinking water source.

The presence of the odorant 2-methylisoborneol (2-MIB) in drinking water sources is undesirable. Although 2-MIB production is known to be influenced by temperature, its regulation at the gene level and its relationship with Chlorophyll-a (Chl-a) at different temperatures remain unclear. This study investigates the impact of temperature on 2-MIB production and related gene expression in Pseudanabaena strains PD34 and PD35 isolated from Lake Paldang, South Korea. The strains were cultured at three temperatures (15, 25, and 30 °C) to examine cell growth, 2-MIB production, and mic gene expression levels. 2-MIB production per cell increased with higher temperatures, whereas mic gene expression levels were higher at lower temperatures, indicating a complex regulatory mechanism involving post-transcriptional and enzyme kinetics factors. Additionally, the relationship between Chl-a and 2-MIB involved in metabolic competition was analyzed, suggesting that high temperatures appear to favor 2-MIB synthesis more than Chl-a synthesis. The distinct difference in the total amount of the two products and the proportion of 2-MIB between the two strains partially explains the variations in 2-MIB production. These findings highlight the significant effect of temperature on 2-MIB biosynthesis in Pseudanabaena and provide a valuable background for gene data-based approaches to manage issues regarding 2-MIB in aquatic environments.

Groundwater is an essential drinking water source for humans. However, improper groundwater management leads to fecal contamination and waterborne diseases caused by viral pathogens. Therefore, this study aimed to investigate norovirus (NoV) contamination by conducting nationwide monitoring over five years (2019–2023). Groundwater samples were analyzed for water quality parameters, indicator microorganisms, NoV prevalence, and viral genotypes. Water quality was assessed for temperature, turbidity, and residual chlorine, whereas microorganisms were analyzed for total coliforms, Escherichia coli, and NoV genotypes. Of the 600 sites, 11 (1.8%) were NoV-positive, irrespective of season or location. Low residual chlorine levels (0.02–0.75 mg/L) were observed, possibly limiting viral inactivation. Total coliforms were detected in only three NoV-positive samples, and E. coli was absent. NoV genotypes were identified as GI.1 and GII.4, with GII.4 being the most frequently detected genotype. The present study demonstrated that periodic monitoring and expanded nationwide efforts are required for effective groundwater management and public health protection.

We investigated the abundance of Pseudanabaena species and the concentration of the monoterpene 2-methylisoborneol (2-MIB) from July to October at three sampling sites in South Korea. To identify the main cause of 2-MIB occurrence in drinking water source, we characterized and performed a phylogenetic analysis of the 2-MIB synthase gene. Pseudanabaena was the dominant cyanobacterium (68–100%) among the samples. At all three sampling sites, a strong positive correlation was detected between 2-MIB concentrations and Pseudanabaena cell numbers. A phylogenetic analysis of 222 MIB sequences isolated from the water samples showed that all of the clones were affiliated with the Pseudanabaena MIB synthase gene, demonstrating that the 2-MIB in Han River drinking water source was produced by Pseudanabaena sp. Using a clone of the 2-MIB gene, network-based analysis and unweighted pair group method with arithmetic mean (UPGMA) analysis were used to examine temporal and spatial variation in the 2-MIB concentration and Pseudanabaena abundance. The network analysis showed greater temporal than spatial similarity among the 2-MIB gene clones. Together, our results demonstrate that Pseudanabaena was the main producer of 2-MIB. These findings provide important information for odor management in drinking water source.