AIMS: To study the cellular growth and morphology of Yarrowia lipolytica W29 and its lipase and protease production under increased air pressures.

METHODS AND RESULTS: Batch cultures of the yeast were conducted in a pressurized bioreactor at 4 and 8 bar of air pressure and the cellular behaviour was compared with cultures at atmospheric pressure. No inhibition of cellular growth was observed by the increase of pressure. Moreover, the improvement of the oxygen transfer rate (OTR) from the gas to the culture medium by pressurization enhanced the extracellular lipase activity from 96.6 U L^-1 at 1 bar to 533.5 U L^-1 at 8 bar. The extracellular protease activity was reduced by the air pressure increase, thereby eliciting further lipase productivity. Cell morphology was slightly affected by pressure, particularly at 8 bar, where cells kept the predominant oval form but decreased in size.

CONCLUSIONS: OTR improvement by total air pressure rise up to 8 bar in a bioreactor can be applied to the enhancement of lipase production by Y. lipolytica. 

SIGNIFICANCE AND IMPACT OF THE STUDY: Hyperbaric bioreactors can be successfully applied for yeast cells cultivation, particularly in high-density cultures used for enzymes production, preventing oxygen limitation and consequently increasing overall productivity.