Table 1: Low and high levels of each variable used in Plackett-Burman design.

VariablesMedium components+values (g/L)−values (g/L)

Starch202.0
Yeast extract80.8
Peptone40.4
MgSO420.2
KBr0.20.02
FeSO4·7H2O0.080.008
CaCO340.4