Abstract
Backgroundd-Lactate is a valued chemical which can be produced by some bacteria including Klebsiella pneumoniae. However, only a few studies have focused on K. pneumoniae for d-lactate production with a significant amount of by-products, which complicated the purification process and decreased the yield of d-lactate.ResultsBased on the redirection of carbon towards by-product formation, the effects of single-gene and multiple-gene deletions in K. pneumoniae on d-lactate production from glucose via acetolactate synthase (budB), acetate kinase (ackA), and alcohol dehydrogenase (adhE) were tested. Klebsiella pneumoniae mutants had different production behaviours. The accumulation of the main by-products was decreased in the mutants. The triple mutant strain had the most powerful ability to produce optically pure d-lactate from glucose, and was tested with xylose and arabinose as carbon sources. Fed-batch fermentation was also carried out under various aeration rates, and the strain accumulated 125.1 g/L d-lactate with a yield of 0.91 g/g glucose at 2.5 vvm.ConclusionsKnocking out by-product synthesis genes had a remarkable influence on the production and yield of d-lactate. This study demonstrated, for the first time, that K. pneumoniae has great potential to convert monosaccharides into d-lactate. The results provide new insights for industrial production of d-lactate by K. pneumoniae.
Highlights
Background dLactate is an important chiral chemical with widespread applications in herbicides, coatings, adhesive, spices, and cosmetics. d-Lactate is an excellent monomer for polylactate (PLA) production, a biodegradable plastic
The properties of PLA depend on the monomer composition, and different monomers can be polymerized into different bioplastics, such as poly l-lactate (PLLA), poly d-lactate (PDLA), and poly d, l-lactate (PDLLA)
Effect of gene deletion on cell growth To investigate the effects of single-gene deletion or multigene deletions of budB, acetate kinase (ackA), and alcohol dehydrogenase (adhE) on cell growth, the gene-deficient mutants and wild-type strain were cultured under the same conditions in shake flask (Fig. 1)
Summary
Background dLactate is an important chiral chemical with widespread applications in herbicides, coatings, adhesive, spices, and cosmetics. d-Lactate is an excellent monomer for polylactate (PLA) production, a biodegradable plastic. D-Lactate is an excellent monomer for polylactate (PLA) production, a biodegradable plastic. The properties of PLA depend on the monomer composition, and different monomers can be polymerized into different bioplastics, such as poly l-lactate (PLLA), poly d-lactate (PDLA), and poly d, l-lactate (PDLLA). Stereocomplex PLA (PDLLA, or sc-PLA), prepared by blending PLLA and PDLA at different ratios, has a Biosynthesis of chemicals has attracted great attention because of its high efficiency, sustainable development, and ability to alleviate dependence on petroleum-based materials. D-Lactate can be produced by fermentation using wild-type microbes, such as Lactobacillus [3], Sporolactobacillus [4] and metabolic engineered strains, including those of the Escherichia [5], Saccharomyces [6], and Klebsiella [7] genera. Blocking the by-products synthesized during metabolic engineering is a primary solution to improve d-lactate production.
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