VTT Technical Research Centre of Finland, P,O, Box 1000, FI-02044 VTT, Finland.
BMC Biotechnol. 2010 Aug 26;10:63. doi: 10.1186/1472-6750-10-63.
The D-galacturonic acid derived from plant pectin can be converted into a variety of other chemicals which have potential use as chelators, clarifiers, preservatives and plastic precursors. Among these is the deoxy-keto acid derived from L-galactonic acid, keto-deoxy-L-galactonic acid or 3-deoxy-L-threo-hex-2-ulosonic acid. The keto-deoxy sugars have been found to be useful precursors for producing further derivatives. Keto-deoxy-L-galactonate is a natural intermediate in the fungal D-galacturonate metabolic pathway, and thus keto-deoxy-L-galactonate can be produced in a simple biological conversion.
Keto-deoxy-L-galactonate (3-deoxy-L-threo-hex-2-ulosonate) accumulated in the culture supernatant when Trichoderma reesei Δlga1 and Aspergillus niger ΔgaaC were grown in the presence of D-galacturonate. Keto-deoxy-L-galactonate accumulated even if no metabolisable carbon source was present in the culture supernatant, but was enhanced when D-xylose was provided as a carbon and energy source. Up to 10.5 g keto-deoxy-L-galactonate l(-1) was produced from 20 g D-galacturonate l(-1) and A. niger ΔgaaC produced 15.0 g keto-deoxy-L-galactonate l(-1) from 20 g polygalacturonate l(-1), at yields of 0.4 to 1.0 g keto-deoxy-L-galactonate g D-galacturonate consumed. Keto-deoxy-L-galactonate accumulated to concentrations of 12 to 16 g l(-1) intracellularly in both producing organisms. This intracellular concentration was sustained throughout production in A. niger ΔgaaC, but decreased in T. reesei.
Bioconversion of D-galacturonate to keto-deoxy-L-galactonate was achieved with both A. niger ΔgaaC and T. reesei Δlga1, although production (titre, volumetric and specific rates) was better with A. niger than T. reesei. A. niger was also able to produce keto-deoxy-L-galactonate directly from pectin or polygalacturonate demonstrating the feasibility of simultaneous hydrolysis and bioconversion. Although keto-deoxy-L-galactonate accumulated intracellularly, concentrations above ~12 g l(-1) were exported to the culture supernatant. Lysis may have contributed to the release of keto-deoxy-L-galactonate from T. reesei mycelia.
植物果胶中的 D-半乳糖醛酸可以转化为多种其他化学物质，这些物质具有作为螯合剂、澄清剂、防腐剂和塑料前体的潜在用途。其中一种是 L-半乳糖醛酸衍生的脱氧酮酸、酮基脱氧-L-半乳糖酸或 3-脱氧-L-苏型-己-2-酮糖酸。已经发现酮基脱氧糖是进一步衍生的有用前体。酮基脱氧-L-半乳糖酸盐是真菌 D-半乳糖醛酸代谢途径中的天然中间产物，因此可以通过简单的生物转化来生产酮基脱氧-L-半乳糖酸盐。
当曲霉菌 Δlga1 和黑曲霉 ΔgaaC 在 D-半乳糖醛酸盐存在下生长时，酮基脱氧-L-半乳糖酸盐（3-脱氧-L-苏型-己-2-酮糖酸）在培养上清液中积累。即使培养上清液中没有可代谢的碳源，酮基脱氧-L-半乳糖酸盐也会积累，但当提供 D-木糖作为碳和能源源时，酮基脱氧-L-半乳糖酸盐会增强。从 20g D-半乳糖醛酸盐 l(-1)中生产了 10.5g 酮基脱氧-L-半乳糖酸盐 l(-1)，黑曲霉 ΔgaaC 从 20g 聚半乳糖醛酸盐 l(-1)中生产了 15.0g 酮基脱氧-L-半乳糖酸盐 l(-1)，产率为 0.4 至 1.0g 酮基脱氧-L-半乳糖酸盐 g D-半乳糖醛酸盐消耗。在两种产生菌中，酮基脱氧-L-半乳糖酸盐在细胞内积累到 12 至 16g l(-1)的浓度。在黑曲霉 ΔgaaC 中，这种细胞内浓度在整个生产过程中都能维持，但在曲霉菌中会下降。
用黑曲霉 ΔgaaC 和曲霉菌 Δlga1 实现了 D-半乳糖醛酸盐向酮基脱氧-L-半乳糖酸盐的生物转化，尽管黑曲霉的生产（产量、体积和比速率）优于曲霉菌。黑曲霉还能够直接从果胶或聚半乳糖醛酸盐生产酮基脱氧-L-半乳糖酸盐，证明了同时水解和生物转化的可行性。尽管酮基脱氧-L-半乳糖酸盐在细胞内积累，但浓度超过~12g l(-1)会被运送到培养上清液中。裂解可能有助于酮基脱氧-L-半乳糖酸盐从曲霉菌菌丝体中释放。
