Optical density, chlorophyll, carotenoids and oil contents were the highest at 10
mM malonate; higher concentrations were inhibitory (with few exceptions). Rates of
respiratory oxygen uptake also decreased at malonate concentrations above 10 mM.
Dry mass was, however, continually increasing by increased malonate
concentrations. Free glycerol contents have not been generally altered by malonate
concentrations, with few exceptions. The above-mentioned observations were
consistent at all of the studied species (local isolates of Chlorococcum humicola,
Scenedesmus dimorphus, Scenedesmus acutiformis and Scenedesmus quadricauda),
except in the dry mass of Chlamydomonas (SAG isolate (Samlung für Algen
kulturen).
The inhibitory action on respiration by malonate concentration above 10 mM was
accompanied by lipoid decrease. Thus, the hypothesis of competitive inhibition of
succinate dehydrogenase (SD) by malonate, with increased acetyl CoA and
subsequently triglycerides, is ruled out at malonate concentration above 10 mM.
Increased oil yield at ≤ 10 mM malonate resulted from increased culture cell density
along with increased oil content per cell. Doubling oil and dry mass contents in one
litre (10 mM) of the studied algae roughly costs 0.23€.