# Effects of Climate Change on 2-Methyllisoborneol Production in Two Cyanobacterial Species
## 1 Introduction  
The combustion of fossil fuels during the past two centuries has significantly increased the atmospheric carbon dioxide (CO\({}_{2}\)) concentration, a trend that has been projected to continue over the coming decades [1]. Atmospheric CO\({}_{2}\) concentrations that had previously increased at a rate of 1% per year in the 20 th century are now increasing at 3% per year and may exceed 900 ppm. Furthermore, there may be a more than 2 \({}^{\circ}\)C increase by 2100 [1, 2]. If the concentration of CO\({}_{2}\) in the atmosphere increased from 350 to 900 ppm, the pH and dissolved inorganic carbon (DIC) in water bodies would change. The carbonate ion concentration (\(\text{c}_{\text{CO}_{3}^{2-}}\)) would decrease while the concentration of bicarbonate ions (\(\text{c}_{\text{CO}_{3}^{2-}}\)) would increase [3, 4, 5, 6, 7]. Since a natural water body is an open system,the CO\({}_{2}\) exchange between air and water is a long-term and stable process, and so are its effects on cyanobacteria and green algae [8]. [PERSON] et al. reported that the microcystin concentration in water declined when CO\({}_{2}\) concentrations increased [7]. Figure 1 shows the longitudinal carbon cycling in the water environment, and the increase in atmospheric CO\({}_{2}\) concentration has an effect on the inorganic carbon in the water. Algal cells transport HCO\({}_{3}\)\({}^{-}\) into the cytosol via plasma membrane active transport and HCO\({}_{3}\)\({}^{-}\) is converted to CO\({}_{2}\) in the cells by carbonic anhydrase [9]. An increased atmospheric CO\({}_{2}\) concentration changes cyanobacteria and algae growth because it alters the open water carbonate equilibrium, although this effect is buffered to some degree by the carbonate equilibrium. Furthermore, substantial CO\({}_{2}\) increases also affect carbon sequestration. The effect on filamentous bacteria is even more obvious [10]. Under high temperature conditions in summer, especially during heat waves, the inorganic carbon utilization mechanism becomes more effective [3; 11]. Harmful algal blooms caused by cyanobacteria have been reported in scientific literature for more than 130 years [12]. It is one of the most important waterborne microbial hazards to human and freshwater ecosystems [13]. Periodic taste and odor events are common problems that influence the water quality in reservoirs and lakes [14; 15]. 2-Methylisoborneol (2-MIB), geosmin, and other volatile organic compounds are the primary off-flavor compounds in surface and drinking water [16; 17]. The odorous 2-MIB is a secondary metabolite produced by cyanobacteria, such as _Dolichosperm_ sp., _Planktonrix_ sp., _Pseudanabaena_, and _Oscillatoria_ sp. [18; 19; 20]. 2-MIB is synthesized in algal cells. The natural substrate (\(E\))-2-methylgeranyl diphosphate (3,2-MeGPP) is formed from the methyl group \(S\)-adenosyl-L-methionine (SAM) and 2-MIB is synthesized from MeGPP by 2-methylisoborneol synthase (MIBS) [21; 22]. The presence of 2-MIB in source waters decreases the water quality, and the smell in water leads to frequent complaints from consumers [23]. Furthermore, _Planktothrix_ sp. has been identified as a potential 2-MIB producer [18]. Extracellular and intracellular 2-MIB are produced from different algae organic matter (AOM) fractions [24; 25; 26; 27]. Aqueous AOMs are derived from algae metabolites that are generally categorized into extracellular organic matter and intracellular organic matter [28]. Natural organic matters present in surface water are complex and multiphase mixtures consisting of humic acids, fulvic acids, low molecular weight organic acids, carbohydrates, proteins, and other compounds [29]. Dissolved organic matters (DOMs) include organic molecules with chromophoric (light absorbing) and fluorophoric (light emitting) moieties. The fluorescence excitation-emission matrix (EEM) analysis of water samples has become increasingly common because it can interpret the fluorescence characteristics of DOM with a high degree of sensitivity [30].