The freshwater alga Chlorella, a highly productive source of starch, might substitute for starch-rich terrestrial plants in bioethanol production. The cultivation
conditions necessary for maximizing starch content in Chlorella biomass, generated in outdoor scale-up solar photobioreactors, are described. The most important factor
that can affect the rate of starch synthesis, and its accumulation, is mean illumination resulting from a combination of biomass concentration and incident light intensity. While 8.5% DW of starch was attained at a mean light intensity of 215 mmol/(m2s1),40% of DW was synthesized at a mean light intensity 330 mmol/(m2s1). Another important factor is the phase of the cell cycle. The content of starch was highest (45% of DW) prior to cell division, but during the course of division, its cellular level rapidly decreased to about 13% of DW in cells grown in light, or to about 4%
in those kept in the dark during the division phase. To
produce biomass with high starch content, it is necessary to
suppress cell division events, but not to disturb synthesis of
starch in the chloroplast. The addition of cycloheximide
(1mg/L), a specific inhibitor of cytoplasmic protein synthesis, and the effect of element limitation (nitrogen, sulfur,phosphorus) were tested. The majority of the experiments
were carried out in laboratory-scale photobioreactors, where
culture treatments increased starch content to up to about
60% of DWin the case of cycloheximide inhibition or sulfur
limitation. When the cells were limited by phosphorus or
nitrogen supply, the cellular starch content increased to 55%
or 38% of DW, respectively, however, after about 20 h,
growth of the cultures stopped producing starch, and the
content of starch again decreased. Sulfur limited and cycloheximide-treated cells maintained a high content of starch
(60% of DW) for up to 2 days. Sulfur limitation, the most
appropriate treatment for scaled-up culture of starchenriched biomass, was carried out in an outdoor pilot-scale
experiment. After 120 h of growth in complete mineral
medium, during which time the starch content reached
The freshwater alga Chlorella, a highly productive source of starch, might substitute for starch-rich terrestrial plants in bioethanol production. The cultivationconditions necessary for maximizing starch content in Chlorella biomass, generated in outdoor scale-up solar photobioreactors, are described. The most important factorthat can affect the rate of starch synthesis, and its accumulation, is mean illumination resulting from a combination of biomass concentration and incident light intensity. While 8.5% DW of starch was attained at a mean light intensity of 215 mmol/(m2s1),40% of DW was synthesized at a mean light intensity 330 mmol/(m2s1). Another important factor is the phase of the cell cycle. The content of starch was highest (45% of DW) prior to cell division, but during the course of division, its cellular level rapidly decreased to about 13% of DW in cells grown in light, or to about 4%in those kept in the dark during the division phase. Toproduce biomass with high starch content, it is necessary tosuppress cell division events, but not to disturb synthesis ofstarch in the chloroplast. The addition of cycloheximide(1mg/L), a specific inhibitor of cytoplasmic protein synthesis, and the effect of element limitation (nitrogen, sulfur,phosphorus) were tested. The majority of the experimentswere carried out in laboratory-scale photobioreactors, whereculture treatments increased starch content to up to about60% of DWin the case of cycloheximide inhibition or sulfur
limitation. When the cells were limited by phosphorus or
nitrogen supply, the cellular starch content increased to 55%
or 38% of DW, respectively, however, after about 20 h,
growth of the cultures stopped producing starch, and the
content of starch again decreased. Sulfur limited and cycloheximide-treated cells maintained a high content of starch
(60% of DW) for up to 2 days. Sulfur limitation, the most
appropriate treatment for scaled-up culture of starchenriched biomass, was carried out in an outdoor pilot-scale
experiment. After 120 h of growth in complete mineral
medium, during which time the starch content reached
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