Carotenoids content of Botryococcus braunii displayed low nitrate demand; the concentration of 3.2 mM
nitrate (50% of Chu 13 medium) resulted in most of the growth magnitude whereas carotenoids increments
were highest at 25% (1.6 mM) nitrate. P
(net photosynthetic oxygen evolution) and carotenoids content
responded opposite to each other at supplemental bicarbonate; carotenoids have been enhanced at low
concentrations (0, 1 or 5 mM), being highest at 100% nitrate (6.4 mM) while P
N
was significantly enhanced
at higher concentrations (10, 15 and 20 mM) and vice versa. Enhanced P
N
N
at high carbon and nitrogen may
have shifted the metabolism to amino acid synthesis thus inhibiting hydrocarbons synthesis. NaCl (0.15
or 0.2 M) increased carotenoids content 5 times that of the control (zero NaCl) whereas higher salinity
concentrations (0.25 and 0.3 M NaCl) were relatively inhibitory. Salinity, in addition, abolished the usual
preferential effect of nitrate concentrations on carotenoids accumulation since their level was only slightly
less at 6.4 mM than at 50% this concentration (3.2 mM). Collectively, NaCl (0.1-0.2 M) induced highest
carotenoids and chlorophyll contents, highest P
N
and lowest R
in 50% nitrate whereas does not have such
effect in 100% nitrate. Botryococcus braunii proved strong capability of adjusting the pH of the medium,
whether acidic or alkaline, back close to the start. Carotenoids content was not responsive to a wide range
of pH values (4-12), exhibiting their highest level at pH 6.
D