Mathematical modeling of Microcystis aeruginosa growth and [D-Leu1] microcystin-LR production in culture media at different temperatures

Abstract

A B S T R A C TThe effect of temperature (26 C, 28 C, 30 C and 35 C) on the growth of native CAAT-3-2005 Microcystis aeruginosa and the production of Chlorophyll-a (Chl-a) and Microcystin-LR (MC-LR) were examined through laboratory studies. Kinetic parameters such as specific growth rate (m), lag phase duration (LPD) and maximum population density (MPD) were determined by fitting the modified Gompertz equation to the M. aeruginosa strain cell count (cells mL À1 ). A 4.8-fold increase in m values and a 10.8-fold decrease in the LPD values were found for M. aeruginosa growth when the temperature changed from 15 C to 35 C. The activation energy of the specific growth rate (Em) and of the adaptation rate (E 1 /LPD) were significantly correlated (R 2 = 0.86). The cardinal temperatures estimated by the modified Ratkowsky model were minimum temperature = 8.58 AE 2.34 C, maximum temperature = 45.04 AE 1.35 C and optimum temperature = 33.39 AE 0.55 C.Maximum MC-LR production decreased 9.5-fold when the temperature was increased from 26 C to 35 C. The maximum production values were obtained at 26 C and the maximum depletion rate of intracellular MC-LR was observed at 30-35 C. The MC-LR cell quota was higher at 26 and 28 C (83 and 80 fg cell À1 , respectively) and the MC-LR Chl-a quota was similar at all the different temperatures (0.5-1.5 fg ng À1 ).The Gompertz equation and dynamic model were found to be the most appropriate approaches to calculate M. aeruginosa growth and production of MC-LR, respectively. Given that toxin production decreased with increasing temperatures but growth increased, this study demonstrates that growth and toxin production processes are uncoupled in M. aeruginosa. These data and models may be useful to predict M. aeruginosa bloom formation in the environment.

Cyanobacteria Growth Kinetics

“…The ratio of the specific growth rate to the lag time duration was approximately constant, suggesting a linear relationship between lag phase and the reciprocal of the growth rate. This finding was corroborated by Crettaz Minaglia [39], who reported that the lag phase showed a linear behavior with the reciprocal specific growth rate for M. aeruginosa. The correlation coefficient (R 2 ) was 0.86.…”

“…Crettaz Minaglia [39] found that the production of MC-LR decreased with increasing temperature, coinciding with the findings of [43][44][45][46][47][48][49][50].…”

“…The Gompertz parameters of these curves were reported by Crettaz Minaglia et al [39]. It can be seen that as the temperature increases, the value of μ increases and LPD decreases.…”

“…Generation time was defined as the time for the bacterial population to double in cell numbers and was calculated by dividing μ values by 0.301 (equivalent to log 10 2); GT is thus a measure of the metabolic rate in a new environment. The RLPD, defined by the amount of work to be done in adjusting to a new environment and the rate at which that work is done, was calculated by dividing LPD by GT [39].…”

“…Paerl [38] reported the optimum temperature to be higher than 25°C, overlapping with that of green algae (27-32.8°C) but clearly differing from that of dinoflagellates (17-27°C) and diatoms (17-22°C). Crettaz Minaglia [39] reported the optimum growth temperature for native M. aeruginosa to be 33.39 ± 0.55°C.…”