Presence of the bacterial hemoglobin gene improves alpha-amylase production of a recombinant Escherichia coli strain.

A recombinant plasmid (pMK57) was constructed by cloning the Bacillus stearothermophilus alpha-amylase gene into pUC8; plasmid pMK79 was then derived from pMK57 by inserting the bacterial (Vitreoscilla) hemoglobin gene into the latter plasmid. Both pMK57 and pMK79 were transformed into Escherichia coli strain JM 103 to make strains MK57 and MK79, respectively. Both MK57 and MK79 produced alpha-amylase and MK79 produced hemoglobin. MK79 outgrew MK57 in shake flasks in LB medium, the advantage of the former appearing in late log phase. MK79 produced more alpha-amylase than MK57, on both per cell and per volume bases, in both mid and late log phases; the maximum advantage of MK79 (on a per volume basis) occurred in late log phase, at which time it produced 3.3 times as much alpha-amylase as MK57. The numbers of copies per cell of both pMK57 and pMK79 were significantly lower than that of pUC8.