For example, there is a process which comprises performing culturing from the late logarithmic growth phase to stationary growth phase in an inorganic medium containing about 0.05 wt % to 5.0 wt % of D-glucose, about 0.01 wt % to 1.0 wt % of alkanoic acid or alkane, collecting bacterial cells by centrifugal separation and then further culturing in an inorganic medium containing about 0.01 wt % to