Influence of Vitreoscilla hemoglobin gene expression on 2,3-butanediol production in Klebsiella oxytoca

Abstract

A hemoglobin-like protein is a protein that aids in the delivery of oxygen in microbes in a similar fashion as hemoglobins in plants and animals. In this study, expression of Vitreoscilla hemoglobin (VHb) was used to improve the growth of Klebsiella oxytoca, and consequently, the 2,3-butanediol (2,3-BDO) production. The Vitreoscilla hemoglobin gene (vgb) was cloned into the expression vector pET-24a, and the recombination plasmid was then transformed in Klebsiella oxytoca ATCC43863. The efficiency of 2,3-BDO production and cell growth was analyzed by placing VHb expression under the control of the nar and luxS promoters instead of the T7 in Klebsiella oxytoca. Fermentation experiments were performed for comparison with the wild type under conditions of high/low aeration for the optimization of VHb-expressing cells in a 500 mL shaking flask and a 5 L fermenter. Moreover, cultivations were performed with addition of acetic acid to the culture media to study the effects of acetic acid on 2,3-BDO production, as acetic acid is known to induce 2,3-BDO production. The results indicated a 10% increase of cell growth in the presence of VHb, while 2,3-BDO production was further improved by the addition of acetic acid. In particular, the fed-batch fermentation of Klebsiella oxytoca LV with acetic acid added exhibited increase of the dry cell weight from 11.9 to 14.0 g/L, and improvement of the 2,3-BDO production from 34.9 to 49.4 g/L in 40 h.