Bioconversion of d-xylose to d-xylonate with Kluyveromyces lactis

Metabolic engineering of Saccharomyces cerevisiae for bioconversion of d-xylose to d-xylonate

“…Previously the best D-xylonate production levels with yeast have been reported for K. lactis expressing the T. reesei xyd1 gene (Nygård et al, 2011). Compared to the K. lactis xyd1 strain the S. cerevisiae CEN.PK xylB strain produced 42 fold more D-xylonate at a higher volumetric production rate, while producing less xylitol.…”

“…The frozen pellets were freeze-dried using a Christ Alpha 2-4 lyophiliser (Biotech international, Belgium), removing all excess moisture. Intracellular D-xylonate, D-xylose and xylitol were extracted from the lyophilized pellets ( $ 60 mg biomass ml À 1 ) in 5 mM H 2 SO 4 , as described by Nygård et al (2011). Cell debris was removed by centrifugation and the supernatant analysed by HPLC.…”

“…However, for an industrial production process, an inhibitor tolerant organism such as the yeast Saccharomyces cerevisiae expressing a D-xylose specific Dxylose dehydrogenase would be advantageous. We recently described D-xylonate production with S. cerevisiae (Toivari et al, 2010) and Kluyveromyces lactis (Nygård et al, 2011) using D-xylose preferring D-xylose dehydrogenase from T. reesei (Berghäll et al, 2007). The activity of the T. reesei D-xylose dehydrogenase was relatively low in both hosts, even though the encoding gene was expressed in multiple copies.…”

Genetic improvement of microorganisms for applications in biorefineries

“…Although wild type bacteria are efficient in the xylonic acid production, they still have high nutritional requirements, and low cell biomass production yields, which makes their utilization in industrial processes difficult. Consequently, for the last three years, genetic engineering strategies were used to build recombinant xylonic acid producing strains of E. coli, S. cerevisiae, Kluyveromyces lactis and Pichia kudriavzevii [50][51][52][53][54][55]. These microorganisms were chosen as possible hosts for presenting high growth rates, simple nutritional requirements and specially yeasts, for presenting good tolerance to inhibitors found in lignocellulosic hydrolysates, as commented above [45].…”

“…These microorganisms were chosen as possible hosts for presenting high growth rates, simple nutritional requirements and specially yeasts, for presenting good tolerance to inhibitors found in lignocellulosic hydrolysates, as commented above [45]. Indeed, the identification of genes from different microorganisms, that code for the enzymes involved in the conversion of xylose to xylonic acid allowed construction of strains able to produce xylonic acid with yields above 90% of theoretical maximum and at high concentrations [50][51][52][53][54][55].…”