Effect of temperature on
growth, chemical composition and fatty acid composition of tropical
Australian microalgae grown in batch cultures
S.M. Renaud, Luong-Van Thinh, G. Lambrinidis, D.L.
Parry-2002
Aquaculture, 211(1-4): 195-214
Abstract:
The growth and nutritional content of four tropical
Australian microalgal species, diatom Chaetoceros sp. (CS256), two
cryptomonads, Rhodomonas sp. (NT15) and Cryptomonas sp.
(CRFI01) and unidentified prymnesiophyte (NT19), cultured at five different
temperatures, were studied. Commercially available Isochrysis sp.
(clone T.ISO) was included in the study for comparison. Microalgae were
grown in laboratory 1.5-l batch cultures in F/2 medium at 25, 27, 30, 33 and
35 °C (salinity 25 ppt; pH 8.3; photon flux density 80 µmol photon m-2
s-1; 12:12 h light:dark cycle). Microalgal cells were harvested
in late logarithmic growth phase and analysed for protein, carbohydrate,
lipid, chlorophyll a, inorganic matter (ash) and fatty acid
composition. The optimum temperature for growth was 25-27 °C for Rhodomonas
sp. (specific growth rate, µ=0.27 day-1), and 27-30 °C
for prymnesiophyte NT19, Cryptomonas sp., Chaetoceros sp. and Isochrysis
sp. (µ=0.56, 0.33, 0.87 and 0.97 day-1, respectively).
Only Chaetoceros sp. grew well at 33 and 35 °C (µ>0.78
day-1). All tropical Australian species had significantly lower
percentages of protein when cells were grown at temperatures above 27 °C,
but there was no consistent trend in the percentages of carbohydrate. Chaetoceros
sp. had highest percentage of lipid (16.8% dry weight; P<0.01),
when cells were cultured at 25 °C, while Rhodomonas sp., Cryptomonas
sp., NT19 and Isochrysis sp., had significantly higher amounts of
lipid at temperatures within the range 27-30 °C (15.5, 12.7, 21.4, and
21.7% dw, respectively; P<0.05 in each case). Considering all
species together, there was no overall relationship between percentage of
protein, carbohydrate or lipid and temperature, but there was an overall,
linear relationship between percentage of ash (inorganic matter) and
temperature (r2=0.42, P</=0.05). Highest
calculated energy values were found in Chaetoceros sp. (21.9 kJ g-1)
and Tahitian Isochrysis sp. (22.5 kJ g-1) cultured at
27-30 °C. There was no significant change in chlorophyll a (range
1.2-1.68 pg cell-1) for any species over the temperature range
studied.
The highly unsaturated fatty acid (HUFA),
eicosapentaenoic acid, 20:5n-3, was present in all species, with
highest amounts in prymnesiophyte NT19 (19.9% total fatty acids).
Percentages of 20:5n-3 were slightly lower at highest growth
temperatures for all species. The control, Isochrysis sp., had the
highest amount of docosahexaenoic acid, 22:6n-3 (6.6% total fatty
acids). All species had lower percentages of 22:6n-3 at higher growth
temperatures. Chaetoceros sp. and NT19 had moderate amounts of
arachidonic acid, 20:4n-6 in the fatty acid profile (2.7-5.4% total
fatty acids). Highest percentages were associated with growth temperatures
within the range 27-30 °C. Only Chaetoceros sp. grew well at 35 °C,
maintaining moderate percentages of protein, carbohydrate, lipid, PUFA and
HUFA (9.6% total fatty acids), at that temperature. All tropical Australian
species performed better than Isochrysis sp., in terms of percentage
of HUFA, over the range of growth temperatures.
(Faculty of Science, Information Technology and
Education, Northern Territory University, Darwin, NT 0909, Australia, Tel.:
+61-8-8946-4730; Fax: +61-8-8946-6847, e-mail: sue.renaud@ntu.edu.au)