Efficient malic acid production from glycerol with Ustilago trichophora TZ1

Abstract

BackgroundThe large surplus of crude glycerol, as main low-value waste stream in biodiesel production, has led to the investigation of new possibilities for the production of value-added chemicals from this feedstock. New and efficient (bio-) catalysts are needed that are able to convert glycerol to versatile chemical building blocks. This would contribute to further develop away from a mainly petroleum based, to a sustainable, bio-based industry. One promising group of discussed building block chemicals are dicarbonic acids.ResultsHere, we report the efficient synthesis of malate from glycerol using Ustilago trichophora RK089, which was identified in a screening of 74 Ustilaginaceae. For economically feasible production that can compete with existing processes, a high productivity is required. By adaptive laboratory evolution, the growth and production rate were increased by 2.5- and 6.6-fold, respectively. Further medium optimization increased the final titer, yield, and overall production rate to 196 g L−1, 0.82 gmal ggly−1, and 0.39 g L−1 h−1, respectively.ConclusionsThis titer is the highest reported for microbial malate production, making U. trichophora TZ1 a promising microbial production host for malate from crude glycerol, especially since it is not genetically engineered. Since this production process starts from an industrial waste stream as substrate and yields an interesting platform chemical, which can be used to replace petro-chemicals, it greatly contributes to a sustainable bio-economy.

Efficient itaconic acid production from glycerol with Ustilago vetiveriae TZ1

“…Recently, we were able to improve malate production, growth rate, and glycerol uptake in U.   trichophora by ALE [40]. Here we used the same re-inoculation scheme in shake flasks applying faster growth rate and consequently higher glycerol uptake rates as selection pressure for all six strains from the last screening in duplicates.…”

“…Even though production values both for malic acid, as well as itaconic acid were improved by ALE, the reached titers and production rates are still low compared to published values [16, 28, 40, 48, 53]. To further improve production properties, medium optimization was performed.…”

“…The concentration of dissolved malic acid in the culture broth of CaCO 3 -buffered cultures was determined to be about 15 g L −1 throughout the cultivation, consequently lowering the osmotic stress for the cells [40]. For itaconic acid, the concentration of dissolved acid in CaCO 3 -buffered water was determined to be about 11 g L −1 (Tim Massmann, personal communication) with precipitation of the residual itaconate as calcium itaconate, strengthening the hypothesis of product inhibition by higher dissolved itaconic acid concentrations in NaOH-titrated bioreactors.…”

Draft Genome Sequences of Itaconate-Producing Ustilaginaceae

“…Previous bioprospecting utilizing glucose or glycerol identified several itaconate-producing Ustilaginaceae (1, 7). The investigated species and strains varied in their product spectra and the amounts of product.…”

“…Among the species Ustilago maydis , individual strains differed highly in their ability to produce organic acids, although the product spectra did not differ. Some of the species investigated, for example Ustilago vetiveriae CBS 131474, produced itaconate only with glycerol as carbon source (1, 7). Also, the pH dependency of itaconate production varied a lot.…”