Intracellular Expression of Vitreoscilla Hemoglobin (VHb) Enhances Total Protein Secretion and Improves the Production of α-Amylase and Neutral Protease in Bacillus subtilis

Abstract

In an attempt to alleviate oxygen limitation during batch cultivations, a heterologous bacterial hemoglobin gene (vhb) of Vitreoscilla was introduced into Bacillus subtilis. Biochemically active VHb, as demonstrated by immunoblot analysis and carbon monoxide binding assay, was intracellularly expressed in B. subtilisfrom an inducible promoter−repressor (spac−lacI). Expression of VHb in oxygen‐limited B. subtilis batch bioreactor cultivations enhanced cell growth, decreased accumulation of acetate, and increased the total protein secreted into the culture medium by approximately 1.5‐fold. In addition, VHb‐expressing B. subtiliscultures exhibited increases of approximately 30% and 5−17% in neutral protease activity and α‐amylase activity, respectively, relative to the parental, VHb‐free strain.