Effect of cultivation mode on a bioprocess for chromium yeast biomass enrichment

Defined cultivation media for yeast growth which contained 278.8 mM of gluc ose and 0.1 mM of chromium(III) added as K2Cr(SO4)(2). 12 H2O was used in b atch and combined batch/fed-batch cultivation mode. In fed batch cultivatio n mode the rate of substrate addition remained constant during growth of ye ast and corresponded to a growth rate of 0.25 h(-1). In both cases the grow th and yeast activity was followed by on line measurement of optical densit y, pH and pO(2) at 30 degrees C. At the end of the bioprocess the concentra tion of protein in yeast biomass was determined off line by the biuret reac tion. Total and organically bound chromium was detected by ETA-AAS. Differe nt cultivation modes affected the total cell protein concentration of yeast grown in media supplemented with chromium. In batch process the protein co ntent represented 25.7% of dry yeast biomass, in contrast in the mixed biop rocess this value was 16.9% one the same period of time. The influence of c ultivation mode on chromium uptake was seen in total chromium accumulation which reached 8.68 +/- 0.16 mu mol g(-1) d.wt. in batch and 1.92 +/- 0.04 m u mol of chromium g(-1) of dry yeast biomass in combined batch/fed-batch cu ltivation mode. The opposite was observed for organically bound chromium. T he 60 % of total accumulated chromium was organically bound during yeast gr owth in combined batch/fed-batch mode. When yeast was grown in batch mode t his value attained 13.5 %. Results suggested that a combined batch/fed-batc h mode of cultivation was more effective over a batch system in chromium bi otransformation to organically bound chromium, regardless of the lower prot ein ratio determined in the yeast biomass.