J. Microbiol. Biotechnol. J. Microbiol. Biotechnol. (2017), 27(7), 1316–1323 https://doi.org/10.4014/jmb.1702.02069 Research Article jmb Review Effects of Environmental Factors on Cyanobacterial Production of Odorous Compounds: Geosmin and 2-Methylisoborneol Hyung-Seok Oh 1 , Chang Soo Lee 2 , Ankita Srivastava 1 , Hee-Mock Oh 1 , and Chi-Yong Ahn 1 * Cell Factory Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon 34141, Republic of Korea Freshwater Bioresources Culture Research Division, Nakdonggang National Institute of Biological Resources, Sangju 37242, Republic of Korea Introduction The naturally occurring compounds geosmin and 2- methylisoborneol (2-MIB) are responsible for musty or earthy tastes and odors in water (Fig. 1). Both geosmin and 2-MIB have extremely low odor thresholds to humans, below 10 ng/l [1]. Geosmin and 2-MIB do not pose a health risk; however, the presence of these compounds in drinking water can lead to consumer distrust. The odorous compounds (OCs) in drinking water supplies have been a major concern throughout the world. These OCs frequently appear in aquatic systems and result in strong odor even at extremely low concentrations. In drinking water treatment plants, common processes such as screening, flocculation, sedimentation, and chlorination did not prove useful for their complete removal [2, 3]. Geosmin and 2-MIB are produced by some cyanobacteria and actinomycetes [4]. Cyanobacteria that have been associated with OCs include Anabaena, Aphanizomenon, Lyngbya, Oscillatoria, Phormidium, Planktothrix, and Pseudanabaena [5]. Anabaena is a common geosmin-producing genus in eutrophic lakes and rivers [6, 7]. In the case of 2-MIB, Planktothrix is a major OC-producing genus [8], but the incidence of 2-MIB problems has been much less frequent than that of geosmin. Planktothrix, accordingly, has not been scrutinized as much as Anabaena. Phylogenetic and evolutionary studies of the geosmin synthesis gene (geoA) recently reached to suggest that this gene has been spread by horizontal gene transfer and has a common origin with the 2-MIB gene [9]. qPCR for geoA showed a better correlation with geosmin concentration than Anabaena cell counting data [10]. Compared with such achievement in genetic studies, physiological research is still bewildering. Universal, optimal conditions for cyanobacterial OC production have not been found. It is likely that different strains have their own specific optimal conditions. Temperature and light intensity are the major factors that affect the growth of cyanobacteria. Most cyanobacteria are known to prefer high temperature (>20 C) for growth, but Anabaena spiroides can grow even at temperatures lower than 8 C [11]. Many filamentous cyanobacteria have the Received: February 27, 2017 Revised: April 5, 2017 Accepted: April 20, 2017 First published online April 21, 2017 *Corresponding author Phone: +82-42-860-4329; Fax: +82-42-860-4594; E-mail: cyahn@kribb.re.kr pISSN 1017-7825, eISSN 1738-8872 Copyright © 2017 by The Korean Society for Microbiology and Biotechnology Geosmin and 2-methylisoborneol (2-MIB), responsible for earthy or musty smell, are a major concern for safe drinking water supplies. This study investigated the effects of environmental factors on odorous compound production and cell growth in cyanobacterial strains. Anabaena sp. FACHB-1384, a 2-MIB producer, was sensitive to low temperature (<20 C). However, geosmin producers, Anabaena sp. Chusori and Anabaena sp. NIER, were sensitive to high light intensity (>100 μmol/m /sec), but not to low temperature. Geosmin concentrations increased under higher nitrate concentrations, being linearly proportional to cell density. A P-limited chemostat showed that P-stress decreased the geosmin productivity and extracellular geosmin amount per cell in Anabaena sp. NIER. However, only 2-MIB productivity was reduced in Planktothrix sp. FACHB-1374 under P-limitation. The extracellular 2-MIB amount per cell remained constant at all dilution rates. In conclusion, high light intensity and P-stress can contribute to the lower incidence of geosmin, whereas 2-MIB reduction could be attainable at a lower temperature. Keywords: Geosmin, 2-methylisoborneol, chemostat, cyanobacteria, Anabaena, Planktothrix