Optimisation of the ferrous iron liquid growth medium for Thiobacillus ferrooxidans (DSM 583) by the Design of Experiment (DOE) methodology

The methodology of Design of Experiment was successfully applied for determ ining the optimal composition of a growth medium for Thiobacillus ferrooxid ans DSM583. In order to increase the bacterial concentration in ferrous liq uid medium, its composition was optimised at pH 1.4 and 30 degrees C in 100 -ml shake flasks through a two-step methodology. The objective of the first design was a screening for pointing out the most important parameters amon g 13 tested (agitation rate and concentrations of 12 chemical compounds). A second design was then carried out (D-optimal design) for the 6 majors par ameters (FeSO4, (NH4)(2)SO4, K2HPO4 CuSO4, ZnSO4 and H3BO3) with three fixe d parameters (agitation rate and CaSO4, MgSO4 concentrations). The optimise d composition of the medium providing the higher bacterial concentration wa s found to be (in g L-1): FeSO4 (100), (NH4)(2)SO4 (10), K2HPO4 (10), CuSO4 (0.001), ZnSO4 (0.001), H3BO3 (0.001), CaSO4 (0.001), and MgSO4 (0.1). At pH 1.4 and under a weak agitation (50 rpm) at 30 degrees C, the resulting b acterial concentration was 14.7 mg protein L-1. This value is 50% greater t han those obtained in the usual medium (0.4 g /L of each compound: (NH4)(2) SO4, K2HPO4 and MgSO4) complemented with 100 g FeSO4 L-1.