The Yarrowia lipolytica lipase LIP2 (YILIP2) gene lip2 and Vitreoscilla hemoglobin gene vgb were co-expressed in Pichia pastoris, both under the control of AOX1 promoter, in order to alleviate respiration limitation under conditions of high cell-density fermentation and enhance YILIP2 production. The results showed that recombinant P. pastoris strains harboring the lip2 and vgb genes (VHb(+)) displayed higher biomass and YILIP2 activity than control strains (VHb(-)). Compared with VHb(-) cells, the expression levels of YILIP2 in VHb-expressing cells when oxygen was not a limiting factor were improved 31.5% in shake-flask culture and 22% in a 10-L fermentor. Under non-limiting dissolved oxygen (DO) conditions, the maximum YILIP2 activity of VHb(+) in a 10-L fermentor reached 33,000 U/mL. Oxygen limitation had a more negative effect on YILIP2 productivity in VHb(-) cells than in VHb(+) cells. The highest YILIP2 activity of VHb(+) cells was approximately 1.84-fold higher than that of VHb- cells at lower DO levels. Moreover, the recombinant strain VHb(+) exhibited a higher specific oxygen uptake rate and achieved higher cell viability under oxygen limiting and non-limiting conditions compared with VHb- cells. Therefore, the above results suggest that intracellular expression of VHb(-) in recombinant P. pastoris has the potential to improve cell growth and industrial enzyme production. (C) 2011 Elsevier Inc. All rights reserved.