Although different promoter systems exist for a controlled or continuous expression of heterologous proteins in P. pastoris, frequently the strong and tightly controlled promoter of alcohol oxidase 1 (AOX1) is applied. The AOX promoter is induced by methanol [6] . Methanol, aside from being the inducer of the promoter is also a carbon/ energy substrate. Generally, in such P. pastoris processes, methanol is the only carbon substrate during the production phase of the AOX1-promoter controlled protein. A drawback is the toxicity of methanol. Generally, methanol concentrations above 3.6% inhibit the yeast growth and lead to death [2] .