Abstract
Lactic acid is the monomeric unit of polylactide (PLA), a bioplastic widely used in the packaging, automotive, food, and pharmaceutical industries. Previously, the yeast Komagataella phaffii was genetically modified for the production of lactate from glycerol. For this, the bovine L-lactate dehydrogenase- (LDH)-encoding gene was inserted and the gene encoding the pyruvate decarboxylase (PDC) was disrupted, resulting in the GLp strain. This showed a yield of 67% L-lactic acid and 20% arabitol as a by-product in batches with oxygen limitation. Following up on these results, the present work endeavored to perform a detailed study of the metabolism of this yeast, as well as perturbing arabitol synthesis in an attempt to increase lactic acid titers. The GLp strain was cultivated in a glycerol-limited chemostat at different dilution rates, confirming that the production of both lactic acid and arabitol is dependent on the specific growth rate (and consequently on the concentration of the limiting carbon source) as well as on the oxygen level. Moreover, disruption of the gene encoding arabitol dehydrogenase (ArDH) was carried out, resulting in an increase of 20% in lactic acid and a 50% reduction in arabitol. This study clarifies the underlying metabolic reasons for arabitol formation in K. phaffii and points to ways for improving production of lactic acid using K. phaffii as a biocatalyst.
Highlights
Lactic acid is a bio-product with a consolidated market
We introduced the gene of the bovine L-lactate dehydrogenase- (LDH) into a strain of K. phaffii, along with engineered overexpression of two transporters—PAS and JEN1p [14]
Lactic acid increased in yield concomitant to an increased dilution rate, which can be described as a Crabtree-like effect
Summary
Lactic acid is a bio-product with a consolidated market. It is the monomeric unit for the production of polylactide (PLA), a biopolymer that has garnered great interest as a biodegradable biological substitute for conventional plastics of petrochemical origin [1,2]. The yeast Komagatataela phaffii (formerly Pichia pastoris) has been of interest for the production of lactic acid, mainly due to its ability to consume glycerol, a plentiful carbon source with low added value. This is considered advantageous as a way to make the biodiesel production chain, of which glycerol is a by-product, more profitable, and to maximize the use of biomass contributing to the biorefinery concept [10,11,12,13]. Several studies demonstrate the efficient use of crude and/or pure glycerol as a carbon source by K. phaffii in the production of heterologous proteins, industrial enzymes and high added-value chemicals [10,14,15,16]
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