In order to alleviate oxygen limitation and improve the yield of poly-gamma-glutamic acid (gamma-PGA) during fermentation, the Vitreoscilla hemoglobin gene (vgb) was integrated into the chromosome of Bacillus subtilis and expressed during gamma-PGA production. The activity of the expressed Vitreoscilla hemoglobin (VHb) was confirmed by CO-difference spectrum. Expression of VHb enhanced cell growth under high viscosity fermentation conditions 1.26-fold and increased the yield of gamma-PGA 2.07-fold. These results indicate that the expression of VHb could be advantageous in high viscosity fermentation media. (C) 2010 Elsevier Ltd. All rights reserved.