Culture and growth of two benthic diatoms species isolated from the Salar del Huasco (North of Chile, 20° S) at different conditions of temperature, light and nutrient

Abstract

Benthic diatoms are cultured usually under laboratory conditions to be used as a food source for other organisms, of
aquaculture interest or for biotechnological applications. Laboratory experiments demonstrate the incidence of the physical
and chemical variables on abundance and growth rates of diatoms. While macronutrients are usually selected and dosed into
common culture mediums to meet the general requirements of a wide range of diatoms, the availability and optimization
of micronutrients are more susceptible to each organism’s particular physiological conditions. The aim of this study was to
characterize the growth of two species of benthic diatoms isolated from the Salar de Huasco in batch cultures at different
conditions of temperature (10, 15 and 20 °C), light intensity (40, 80 and 120 ?mol m-2 s-1) and concentrations of silica (1.06
x 10-4 M Na2SiO3 x 9H2O and 2.12 x 10-4 M Na2SiO3 x 9H2O) and selenium (10-8 M H2SeO3) in f/2 medium, on a lightdark
cycle of 18:6 h. Both Nitzschia epithemioides Grunow in Cleve & Grunow (1880) as Nitzschia sp. showed higher
maximum cell densities (692800 ± 107704 and 649600 ± 68942 cells ml-1, respectively) and exponential growth rates
(1.80±0.56 and 0.97±0.32 div. d-1, respectively) at the highest temperature (20°C). The light intensity to which the cultures
were exposed had no effect on cell density and exponential growth rate in both taxa. Regarding to nutrients, an increase
in silicates concentrations on the culture medium could promote the growth of N. epithemioides and Nitzschia sp. since a
tendency was observed to higher cell densities (1.08 x 106 ± 84,639 and 1.32 x 106 ± 109,038 cells ml-1, respectively) and
exponential growth rates (1.98 ± 0.44 and 0.95 ± 0.18 div. d-1, respectively) with respect at the normal f/2 medium and f/2
medium plus selenium. Simultaneous addition of silicate and selenium to the culture medium increased the maximum cell
density of the two strains under study, but this increase was significant (p = 0.05) only for N. epithemioides and among
the normal f/2 medium (719200 ± 116895 cells ml-1) and the f/2 medium with double the amount of silicate and selenium
(1498800 ± 209599 cells ml-1). However, the exponential growth rates were not significantly different when compared
to those of the control (without the addition of silicate and selenium). In conclusion both N. epithemioides and Nitzschia
sp shown an increased cell density and exponential growth rate at 20 °C. The different light intensities not significantly
influenced the growth of both taxa. An increase in the concentration of silicates or simultaneous increase in silicates
and selenium in the culture medium can be considered as possible strategy to increase cell density of benthic diatom N.
epithemioides in batch cultures.