Comparison of green fluorescent protein expression in two industrial Escherichia coli strains, BL21 and W3110, under co-expression of bacterial hemoglobin.

Vitreoscilla hemoglobin (VHb) has been successfully used to enhance production of foreign proteins in several microorganisms including Escherichia coli. We compared the expression of an oxygen-dependent foreign protein, green fluorescent protein (GFP) under co-expression of VHb in two typical industrial E. coli strains, BL21 (a B derivative) and W3110 (a K12 derivative), which have different metabolic properties. We employed the nar oxygen-dependent promoter for self-tuning regulation of VHb expression due to the natural transition of dissolved oxygen (DO) level during culture. We observed several interesting and differing behaviors in cultures of the two strains. VHb co-expression showed a positive influence on expression, and even on solubility, of GFP in both strains; while strain BL21 had the higher GFP expression level, W3110 showed higher solubility of expressed GFP. GFP expression in strain BL21 was very largely affected by variation of aeration environments, but W3110 was not significantly impacted. We surmised that this arose from different oxygen utilization abilities and indeed the two strains showed different patterns of oxygen uptake rate. Interestingly, the VHb co-expressing W3110 strain exhibited a peculiar increasing pattern of GFP expression during the late culture period even under low aeration conditions and this enhancement was more obvious in large-scale cultures. Therefore, this strain could be successfully employed in practical large-scale production cultures where DO levels tend to be limited.