Abstract
Outbreaks of 2-methylisoborneol (2-MIB) contamination in drinking water sources cause inconvenient odor issues in the water distribution system. In this study, microscopy-based isolation with physiological and molecular phylogenetic characterization were performed to investigate and characterize the 2-MIB odor producers that caused an odor problem in the freshwater system of the North Han River in the autumn of 2018. A benthic cyanobacterium was isolated from 2-MIB odor-issue freshwater samples and was found to be phylogenetically affiliated with Pseudanabaena yagii (99.66% sequence similarity), which was recorded in South Korea for the first time. The 2-MIB synthesis gene sequences from the odor-issue freshwater samples showed 100% similarity with those in the P. yagii strains. Protein sequences of 2-MIB synthase observed in the genome of the isolated strain showed structural and functional characteristics similar to those observed in other Pseudanabaena species. The 2-MIB production rate increased slowly during mat formation on the vessel wall; however, it rapidly increased after the temperature dropped. The 2-MIB gene was continuously expressed regardless of the temperature changes. These results suggest that the 2-MIB odor issue in the North Han River might be caused by the release of 2-MIB from the mat-forming P. yagii species in a low-temperature freshwater environment.
Highlights
The presence of earthy-musty odor compounds in freshwater is a significant problem worldwide, and it has a negative impact on water and aquaculture production [1]
2-MIB concentration showed gradually increased patterns from June, with the highest concentration detected in the samples collected from November, when the temperatures were low. These results suggest that the earthy-musty odor issue in the North Han River could mainly be caused by microbes that produce 2-MIB compounds during the summer season, which are increasingly released during low temperature conditions
The results produced after measuring the odor-causing compounds in freshwater samples revealed that the muddy odor issue in the North Han River might be mainly caused by microbes that produce 2-MIB compounds during the summer season and release them under low temperature conditions
Summary
The presence of earthy-musty odor compounds (geosmin/2-methylisoborneol) in freshwater is a significant problem worldwide, and it has a negative impact on water and aquaculture production [1]. 2-methylisoborneol (2-MIB) is known to cause mold odor in freshwater and water distribution systems [2,3,4,5]. The cyanobacteria genera are known to be the major 2-MIB producers [10] in freshwater systems. The 2MIB-producing species are largely non-heterocystous filamentous organisms, and the odor problems from benthic cyanobacteria are fundamentally harder to resolve than those from cyanobacteria of planktonic origin because of their distribution characteristics in the water sample. In the United States, 2-MIB odor problems in water environments are more than twice as likely to be caused by benthic organisms than planktonic organisms [11]
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