Biosynthesis of Anthraquinone by Cells of Galium mollugo L. Grown in a Chemostat with Limiting Sucrose or Phosphate

Growth and anthraquinone biosynthesis by Galium cells were examinedin steady-state substrate-limited conditions using a chemostatcontinuous culture technique. Steady-state growth was obtainedin both sucrose- and phosphate-limiting conditions for periodsup to 60 d. In sucrose-limiting conditions three growth rateswere investigated with doubling times (t_d) of 25 h, 35 h and40 h, and phosphate-limited growth was obtained at t_d= 35 h.The kinetics of the growth response to a change in limitingsubstrate concentration in sucrose-limiting conditions was examinedand found to follow closely that predicted by the applicationof Monod's (1950) model obtained for micro-organisms. The anthraquinone content of cells grown in phosphate and sucroselimitation was uniformly similar and at a relatively low level(0.68 mg g^–1 dry wt.). When the substrate limitation wasrelieved by the addition of the limiting substrate, either phosphate,or sucrose, anthraquinone synthesis was markedly stimulated.The addition of the anthraquinone precursor, orthosuccinyl benzoicacid (OSB) greatly enhanced anthraquinone synthesis in phosphate-limitingconditions but not in sucrose-limited cells. The results show that growth limitation by phosphate and bysucrose causes a suppression of the rate of synthesis of thesecondary metabolite anthraquinone in Galium cells and suggeststhat the metabolic point of suppression is different in eachcase. Key words: Anthraquinone biosynthesis, Galium, Continuous culture, recursor feeding