Highlights d Early farmers domesticated the milk yeast Kluyveromyces lactis d A dairy lineage of Kluyveromyces marxianus donated the LAC genes to K. lactis d A new Kluyveromyces-specific gene cluster for utilizing cellobiose was identified d K. marxianus carries an integrated cellobiose and lactose utilization gene cluster
Crude glycerol is the main by-product of the biodiesel manufacturing industry (10% w/w). Its use as a substrate in microbial fermentations is a concrete strategy to efficiently address its market surplus. In this study, the conversion of crude glycerol to citric acid, a key biochemical in the emerging bioeconomy, by a wild-type yeast Yarrowia lipolytica DSM 8218 was modelled using the Response Surface Methodology. The model relates C/N mass ratio and crude glycerol concentration to maximize the citric acid yield in flask scale using two different N sources, yeast extract and ammonium sulphate. Under the optimal conditions (yeast extract, C/N 141, glycerol 33 g/L), the conversion yield was 0.249 g/g. The optimal conditions were used for up-scaling a fed-batch fermentation in a 2 L bioreactor highlighting a metabolic shift from mannitol to citric acid when high stirring rates were applied (800 rpm). In these conditions, a morphic transition from pseudo-mycelial form to round-shaped yeast-like cells was observed too.
Highlights d Early farmers domesticated the milk yeast Kluyveromyces lactis d A dairy lineage of Kluyveromyces marxianus donated the LAC genes to K. lactis d A new Kluyveromyces-specific gene cluster for utilizing cellobiose was identified d K. marxianus carries an integrated cellobiose and lactose utilization gene cluster
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