SECONDARY METABOLITE SCALE-UP TO MINIMIZE HOMOLOG IMPURITY LEVELS

A mutant strain of Streptomyces hygroscopicus was found to produce up to 9.0 units/L of an immunoregulant precursor, immunomycin, with up to 3.5% of a lower homolog impurity under either dual fed-batch or batch conditions. Glycerol and valine were key nutrients influencing produc tivity and impurity levels. Soybean oil was successfully substituted f or glycerol as a carbon source to minimize shot additions to batch cul ture. The remainder of the production medium was composed largely of d efined components with the exception of yeast extract. Valine limitati on increased lower homolog formation while decreasing higher homolog f ormation; excess valine decreased lower homolog formation below 2-3% w hile increasing higher homolog formation. Higher homolog formation in the presence of valine seemed to be slower than lower homolog formatio n in the absence of valine. Valine was believed to be the major butyra te precursor; consequently its availability influenced the impurity pr ofile. A preliminary cost analysis suggests that elimination of added valine from the cultivation and replacement of glycerol with soybean o il can result in a 6.6-fold reduction in media costs relative to the o riginal fed-batch process. (C) 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 59: 595-604, 1998.