초록
<P><B>Background</B></P><P>In order to establish a cost-efficient biodiesel biorefinery, valorization of its main by-product, crude glycerol, is imperative. Recently, <I>Ustilago trichophora</I> TZ1 was found to efficiently produce malic acid from glycerol. By adaptive laboratory evolution and medium optimization, titer and rate could be improved significantly.</P><P><B>Results</B></P><P>Here we report on the investigation of this strain in fed-batch bioreactors. With pH controlled at 6.5 (automatic NaOH addition), a titer of 142 ± 1 g L<SUP>−1</SUP> produced at an overall rate of 0.54 ± 0.00 g L<SUP>−1</SUP> h<SUP>−1</SUP> was reached by optimizing the initial concentrations of ammonium and glycerol. Combining the potential of bioreactors and CaCO<SUB>3</SUB> as buffer system, we were able to increase the overall production rate to 0.74 ± 0.06 g L<SUP>−1</SUP> h<SUP>−1</SUP> with a maximum production rate of 1.94 ± 0.32 g L<SUP>−1</SUP> reaching a titer of 195 ± 15 g L<SUP>−1</SUP>. The initial purification strategy resulted in 90 % pure calcium malate as solid component. Notably, the fermentation is not influenced by an increased temperature of up to 37 °C, which reduces the energy required for cooling. However, direct acid production is not favored as at a lowered pH value of pH 4.5 the malic acid titer decreased to only 9 ± 1 g L<SUP>−1</SUP>. When using crude glycerol as substrate, only the product to substrate yield is decreased. The results are discussed in the context of valorizing glycerol with Ustilaginaceae.</P><P><B>Conclusions</B></P><P>Combining these results reveals the potential of <I>U.</I><I>trichophora</I> TZ1 to become an industrially applicable production host for malic acid from biodiesel-derived glycerol, thus making the overall biodiesel production process economically and ecologically more feasible.</P>