ABSTRACTThe yeastKluyveromyces lactishas been a successful host for the production of heterologous proteins for over 30 years. Currently, the galactose-/lactose-inducible and glucose-repressibleLAC4promoter (PLAC4) is the most widely used promoter to drive recombinant protein expression inK. lactis. However, PLAC4is not fully repressed in the presence of glucose and significant protein expression still occurs. Thus, PLAC4is not suitable in processes where tight regulation of heterologous gene expression is required. In this study, we devised a novelK. lactispromoter system that is both strong and tightly controllable. We first tested several different endogenousK. lactispromoters for their ability to express recombinant proteins. A novel hybrid promoter (termed P350) was created by combining segments of twoK. lactispromoters, namely, the strong constitutive PGAP1promoter and the carbon source-sensitive PICL1promoter. We demonstrate that P350is tightly repressed in the presence of glucose or glycerol and becomes derepressed upon depletion of these compounds by the growing cells. We further illustrate the utility of P350-controlled protein expression in shake flask and high-cell-density bioreactor cultivation strategies. The P350hybrid promoter is a strong derepressible promoter for use in autoinduction of one-step fermentation processes for the production of heterologous proteins inK. lactis.IMPORTANCEThe yeastKluyveromyces lactisis an important host for the expression of recombinant proteins at both laboratory and industrial scales. However, the system lacks a tightly regulated promoter that permits controlled expression of heterologous proteins. In this study, we report the engineering of a highly regulated strong hybrid promoter (termed P350) for use inK. lactis. P350is tightly repressed by glucose or glycerol in the medium but strongly promotes gene expression once the carbon source has been consumed by the cells. This feature permits heterologous protein expression to be “autoinduced” at any scale without the addition of a gratuitous inducer molecule or changing feed solutions.
Complete Genome Sequence of Kluyveromyces lactis Strain GG799, a Common Yeast Host for Heterologous Protein Expression
