Effect of aggregate size in cell cultures of Tagetes patula on thiophene production and cell growth

Summary The effect of the size of Tagetes patula (marigolds) cell aggregates on growth and thiophene production in MS-medium was studied. A heterogeneous aggregate suspension was aseptically divided into 7 fractions, each with a defined aggregate diameter range, with subsequent inoculation of the fractions into MS growth medium. Growth occurred in all aggregate fractions and thiophene production increased with increasing aggregate diameter starting at about 3 mm, an effect possibly due to an increasing lack of oxygen in the aggregate centre. Calculations of oxygen concentration profiles in the aggregates showed namely, that the critical aggregate diameter where the oxygen concentration in the aggregate centre becomes very low, is about 3 mm. Aggregates with a diameter exceeding 1.2 cm showed a decreased thiophene production, however, these aggregates were hollow. The thiophenes produced mainly consisted of 5-(4-hydroxy-1-butenyl)1-2,2-bithienyl, which was excreted into the medium.Nomenclature ID_e effective diffusion coefficient (m²s^-1) - c oxygen concentration (mol m^-3) - c_s substrate concentration at surface (mol m^-3) - c_s.exp experimental value of c_s (mol m^-3) - c_eq substrate concentration at equilibrium (mol m^-3) - r_s consumption rate (mol m^-3 s^-1) - d_crit critical aggregate diameter (m) - d_agg aggregate diameter (m) - L length of aggregate (m) - W width of aggregate (m) - t time (s) - r distance from aggregate centre (m) - R radius of aggregate (m) - R(c) oxygen consumption (mol m^-3 s^-1) - V_c convection velocity (m s^-1) - V_m intrinsic maximum consumption rate (mol kg^-1 s^-1) - K_m intrinsic Michaelis Menten constant (mol m^-3) - V_m apparent maximum consumption rate (mol kg^-1 s^-1) - K_m apparent Michaelis Menten constant (mol m^-3) - * multiplication sign