A high-throughput method for measuring growth and loss rates in microalgal cultures

A miniaturized and low-cost assay for algal growth and loss rates, and estimation of compensation light was developed and optimized. Microalgal cultures were grown in white 96-well microplates to estimate specific growth rates at six temperatures, five salinities and eight light levels. Data from black 24-well microplates at six temperatures, five salinities and five light conditions were used in addition to estimate loss rates and compensation light. Absorption and reflection of light were different in the white and black microplates. Growth rates were estimated from daily in vivo fluorescence (IVF) measurements using a microplate reader fitted with a fluorometer. To validate the microplate algal growth assay, IVF was compared with cell counting by flow cytometry. Maximal growth rate for the test alga Pseudochattonella farcimen (Heterokonta) was estimated to 0.52 +/- 0.05 day(-1) at optimal temperatures ranging from 9 to 14A degrees C and salinities 18-26 psu. Lowest value of compensation light as photosynthetic photon flux density (PPFD) was 4.2 A +/- 1.2 mu mol photons m(-2) s(-1), and lowest saturation light, 34.1 A +/- 3.7 mu mol photons m(-2) s(-1), was observed in the temperature range 5-11A degrees C and salinity range 23-28 psu. Minimum loss rate was obtained at temperatures 5-8A degrees C and salinities 26-31 psu. Blooms of P. farcimen have been recorded in nature under conditions similar to those minimizing loss rates rather than maximizing growth rates in this study. The microalgal assay described here allows for a large number of conditions to be tested, and accurate optimal conditions for growth and loss rates to be obtained.