Lipids have been extracted according to Folch et al. (1956). Resulting chloroform and
diethyl ether extracts are weighted separately. Each extract is analysed using the Iatroscan Thin layer chromatography - flame ionization detector system. Lipid classes are
separated on chromarods using double development in hexan : benzene : acetic acid (80 :
20 : 1) and hexan : diethyl ether : acetic acid (97 : 3 : 1) solvents systems.
RESULTS
Chemical composition
The used medium contains sugars (660 mg.l -1 ), amino acids (74.2 µM.l -1 ), lipids (46 mg.l' 1 )
and phosphates (560 uatg.l -1 ). The dissolved amino acids/free amino acids ratio
is 10.3, that is similar to the ratio usually found in natural sea water.
The chloroform extract of the used medium represents 21.7 % of total lipids separated on
Iatroscan. 75 % of the chloroform extract are polar lipids and 10 % are hydrocarbons.
78 % of lipids are recovered with diethyl ether after acidification of the used medium
among which 40 % are fatty acids and 45 % Co chromatography with monoglycerides.
The composition of organic matter in the used medium is about 100 folds as much as that
of sea water and about 10 time as much as that of the surface film. Both our used medium
and the surface film show large amount of lipids and carbohydrates (Garrett, 1967a ;
Daumas et ai, 1976 ; Hunter and Liss, 1981). In addition the surface film is enriched in
bacteria and phytoplankton (Harvey, 1966 ; Brockman et ai, 1976 ; De Souza Lima,
1981). Thus we decided to dilute the initial used medium down to the range of values
expected to be found in the surface film and in sea water (concentrations of 10,1,0.1 and
0.01 %) and to test the effects of the so-diluted used medium on phytoplankton growth.
Effects of increasing concentrations of the used medium and P. tricornutum and P.
micans growth
The highest concentration (10 %) of the used medium induces a marked inhibition of the
algae growth during the first 48 h. It then depresses the algae growth with a 60 % reduction
of its specific growth rate (Fig. 1 and Tab. 1).
The intermediate concentration (1 %) inhibits its growth during the first 24 h. Afterwards,
its growth is not different from that of the control. Its specific growth rate is, even slightly
higher (Tab. 1).
The lowest concentrations (0.1 %, 0.01 %) stimulate the algae growth (Fig.1, Tab. 1).
Similar results are obtained on P. micans growth : total inhibition occurs at high
concentration (10 %) and stimulation at low concentration (0.01 %).
Percentage of used medium in the culture medium
0
0.01
0.1
1
10
of algae
Specific growth rate division, d -1
1.46
2.35
2.32
1.56
0.59
Table. 1 : Effects of the total used medium on P. tricornutum growth.
We checked that the contribution of phosphate to the observed stimulation at low
concentrations of the used medium is unlikely. We also checked that if some crude oil is
still remaining in the used medium, it has no effects as regards the stimulation of growth at
0.1 % and 0.01 % used medium in algae cultures. Besides, we demonstrated that the
possible remaining crude oil is not responsible of the growth inhibition at concentration
10%.
623
diethyl ether extracts are weighted separately. Each extract is analysed using the Iatroscan Thin layer chromatography - flame ionization detector system. Lipid classes are
separated on chromarods using double development in hexan : benzene : acetic acid (80 :
20 : 1) and hexan : diethyl ether : acetic acid (97 : 3 : 1) solvents systems.
RESULTS
Chemical composition
The used medium contains sugars (660 mg.l -1 ), amino acids (74.2 µM.l -1 ), lipids (46 mg.l' 1 )
and phosphates (560 uatg.l -1 ). The dissolved amino acids/free amino acids ratio
is 10.3, that is similar to the ratio usually found in natural sea water.
The chloroform extract of the used medium represents 21.7 % of total lipids separated on
Iatroscan. 75 % of the chloroform extract are polar lipids and 10 % are hydrocarbons.
78 % of lipids are recovered with diethyl ether after acidification of the used medium
among which 40 % are fatty acids and 45 % Co chromatography with monoglycerides.
The composition of organic matter in the used medium is about 100 folds as much as that
of sea water and about 10 time as much as that of the surface film. Both our used medium
and the surface film show large amount of lipids and carbohydrates (Garrett, 1967a ;
Daumas et ai, 1976 ; Hunter and Liss, 1981). In addition the surface film is enriched in
bacteria and phytoplankton (Harvey, 1966 ; Brockman et ai, 1976 ; De Souza Lima,
1981). Thus we decided to dilute the initial used medium down to the range of values
expected to be found in the surface film and in sea water (concentrations of 10,1,0.1 and
0.01 %) and to test the effects of the so-diluted used medium on phytoplankton growth.
Effects of increasing concentrations of the used medium and P. tricornutum and P.
micans growth
The highest concentration (10 %) of the used medium induces a marked inhibition of the
algae growth during the first 48 h. It then depresses the algae growth with a 60 % reduction
of its specific growth rate (Fig. 1 and Tab. 1).
The intermediate concentration (1 %) inhibits its growth during the first 24 h. Afterwards,
its growth is not different from that of the control. Its specific growth rate is, even slightly
higher (Tab. 1).
The lowest concentrations (0.1 %, 0.01 %) stimulate the algae growth (Fig.1, Tab. 1).
Similar results are obtained on P. micans growth : total inhibition occurs at high
concentration (10 %) and stimulation at low concentration (0.01 %).
Percentage of used medium in the culture medium
0
0.01
0.1
1
10
of algae
Specific growth rate division, d -1
1.46
2.35
2.32
1.56
0.59
Table. 1 : Effects of the total used medium on P. tricornutum growth.
We checked that the contribution of phosphate to the observed stimulation at low
concentrations of the used medium is unlikely. We also checked that if some crude oil is
still remaining in the used medium, it has no effects as regards the stimulation of growth at
0.1 % and 0.01 % used medium in algae cultures. Besides, we demonstrated that the
possible remaining crude oil is not responsible of the growth inhibition at concentration
10%.
623