Aeration volume and photosynthetic photon flux affect cell growth and secondary metabolite contents in bioreactor cultures of Morinda citrifolia

To improve their growth and secondary metabolite production, we cultured Morinda citrifolia leaf cells for 3 weeks in bioreactors with different aeration volumes (0.05, 0.1, 0.2, or 0.3 vvm; or 0.05/0.1/0.2/0.3 vvm, as increased at 5-d interval), and photosynthetic photon fluxes (PPF; 0, 15, 30, or 45 mu moL m(-2) s(-1)). Cell growth was greatest (15.6 g L-1 dry weight) at 0.3 vvm whereas the accumulation of secondary metabolites (total anthraquinones, phenolics, and flavonoids) was maximized at 0.1 vvm. A PPF of 15 mu moL m(-2) s(-1) accelerated the accumulation of both cell biomass and metabolites. Dark-culturing suppressed cell growth, while a high PPF (45 mu moL m(-2) s(-1)) inhibited metabolite biosynthesis. Further studies are required to understand the reason for differences in the effect of light on cell growth and secondary metabolite contents in M. citrifolia cell cultures.