Abstract
Abstract Background Second-generation feedstocks such as lignocellulosic hydrolysates are more and more in the focus of sustainable biotechnological processes. Corynebacterium glutamicum, which is used in industrial amino acid production at a million-ton scale, has been engineered towards utilization of alternative carbon sources. As for other microorganisms, the focus has been set on the pentose sugars present in lignocellulosic hydrolysates. Utilization of the hexuronic acids D-galacturonic acid (abundant in pectin-rich waste streams such as peels and pulps) and D-glucuronic acid (a component of the side-chains of plant xylans) for growth and production with C. glutamicum has not yet been studied. Results Neither aldohexuronic acid supported growth of C. glutamicum as sole or combined carbon source, although its genome encodes a putative uronate isomerase sharing 28% identical amino acids with UxaC from Escherichia coli. Heterologous expression of the genes for both uptake and catabolism of D-galacturonic acid and D-glucuronic acid was required to enable growth of C. glutamicum with either aldohexuronic acid as the sole carbon source. When present in mixtures with glucose, the recombinant C. glutamicum strains co-utilized D-galacturonate with glucose and D-glucuronate with glucose, respectively. When transformed with the plasmid for uptake and catabolism of the aldohexuronates, model producer strains were able to grow with and produce from D-galacturonate or D-glucuronate as sole carbon source. Conclusions An easily transferable metabolic engineering strategy for access of C. glutamicum to aldohexuronates was developed and applied to growth and production of the amino acids L-lysine and L-ornithine as well as the terpene lycopene from D-galacturonate or D-glucuronate.
Highlights
Second-generation feedstocks such as lignocellulosic hydrolysates are more and more in the focus of sustainable biotechnological processes
Characteristic of C. glutamicum is the capability of growing on mixtures of different carbon sources with a monoauxic growth [5,6] as opposed to diauxic growth observed for many other microorganisms such as Escherichia coli and Bacillus subtilis [7]
The hexuronic acid utilization and transporter genes originated from E. coli MG1655, whereas the strain E. coli DH5α [38] was used for plasmid construction
Summary
Second-generation feedstocks such as lignocellulosic hydrolysates are more and more in the focus of sustainable biotechnological processes. Corynebacterium glutamicum, which is used in industrial amino acid production at a million-ton scale, has been engineered towards utilization of alternative carbon sources. As for other microorganisms, the focus has been set on the pentose sugars present in lignocellulosic hydrolysates. Corynebacterium glutamicum is a rod-shaped Grampositive aerobic bacterium, which can be found in soil, sewages, vegetables, and fruits [1]. This bacterium is capable of utilizing various sugars as well as organic acids [2]. Characteristic of C. glutamicum is the capability of growing on mixtures of different carbon sources with a monoauxic growth [5,6] as opposed to diauxic growth observed for many other microorganisms such as Escherichia coli and Bacillus subtilis [7]. Its importance has further increased as it was for production of of non-natural products [9] such as isobutanol [15], ethanol [16], putrescine [14,17,18], cadaverine [19], carotenoids and terpenoids [20,21,22,23,24,25], and xylitol [26]
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