title: Bioconversion of D-galacturonate to keto-deoxy-L-galactonate (3-deoxy-L-threo-hex-2-ulosonate) using filamentous fungi.
abstract: BACKGROUND
  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.
  
  
  RESULTS
  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](-1). 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: VTT Technical Research Centre of Finland, P,O, Box 1000, FI-02044 VTT, Finland. marilyn.wiebe@vtt.fi
authors.forename: Marilyn G
authors.initials: MG
authors.lastname: Wiebe
authors.forename: Dominik
authors.initials: D
authors.lastname: Mojzita
authors.forename: Satu
authors.initials: S
authors.lastname: Hilditch
authors.forename: Laura
authors.initials: L
authors.lastname: Ruohonen
authors.forename: Merja
authors.initials: M
authors.lastname: Penttilä
mesh_terms: D001234:Aspergillus niger / Q000378:metabolism*; D001711:Biotransformation; D006603:Hexuronic Acids / Q000378:metabolism*; D007218:Industrial Microbiology / Q000379:methods*; D010368:Pectins / Q000378:metabolism; D013400:Sugar Acids / Q000378:metabolism*; D014242:Trichoderma / Q000378:metabolism*
chemical_list: D006603:Hexuronic Acids; D013400:Sugar Acids; C012991:galactonic acid; C007819:galacturonic acid; D010368:Pectins
references.citation: Biochemistry. 2005 Aug 23;44(33):11234-40
references.pmid: 16101307
references.citation: Microbiology (Reading). 2001 Oct;147(Pt 10):2635-2642
references.pmid: 11577142
references.citation: J Biol Chem. 2007 Sep 7;282(36):26195-201
references.pmid: 17609199
references.citation: Biotechnol Bioeng. 2001 Apr 20;73(2):146-56
references.pmid: 11255162
references.citation: Appl Environ Microbiol. 2010 Jan;76(1):169-75
references.pmid: 19897761
references.citation: Appl Microbiol Biotechnol. 2009 Mar;82(4):597-604
references.pmid: 19159926
references.citation: Mol Microbiol. 2006 Aug;61(4):1060-8
references.pmid: 16879654
references.citation: Fungal Genet Biol. 2008 Nov;45(11):1449-57
references.pmid: 18768163
references.citation: Nat Biotechnol. 2008 May;26(5):553-60
references.pmid: 18454138
references.citation: Biotechnol Bioeng. 1983 Aug;25(8):1981-7
references.pmid: 18551544
references.citation: Biochem J. 1999 Nov 1;343 Pt 3:563-70
references.pmid: 10527934