Production of alpha-amylase in fed batch cultures of vgb(+) and vgb(-) recombinant Escherichia coli: Some observations

Synthesis and excretion of Bacillus stearothermophilus cl-amylase is analyz ed in fed-batch cultivations of Escherichia coli JM103[pMK79] and E. coli J m103[pMK57], the former strain containing the plasmid-encoded Vitreoscilla hemoglobin (VHb) gene (vgb) and the latter strain being devoid of this gene . Fed-batch operation is observed to be substantially superior to batch ope ration as concerns the alpha-amylase production rate and the extent of excr etion of the enzyme. Faster feeding of a nutrient medium (LB or M9) discour ages synthesis of a-amylase. While synthesis of cl-amylase in the vgb(-)str ain is discouraged when oxygen availability is reduced, the reverse is the case with the vgb(+) strain, the promotion of cl-amylase synthesis in the l atter strain being linked to the synthesis of VHb. Increased availability o f the principal carbon source (glucose) in a defined medium leads to overpr oduction of both alpha-amylase and VHb under oxygen limitation, which may b e responsible for the segregational instability observed with the vgb+ stra in. The very high extents of excretion of a-amylase attained in fed-batch c ultures are encouraging for downstream processing of the recombinant protei n.