The intracellular galactoglycome in Trichoderma reesei during growth on lactose

Levente Karaffa, Leon Coulier, Erzsébet Fekete, Karin M. Overkamp, Irina S. Druzhinina, Marianna Mikus, Bernhard Seiboth, Levente Novák, Peter J. Punt, Christian P. Kubicek

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10 Citations (Scopus)

Abstract

Lactose (1,4-0-β-d-galactopyranosyl-d-glucose) is used as a soluble carbon source for the production of cellulases and hemicellulases for - among other purposes - use in biofuel and biorefinery industries. The mechanism how lactose induces cellulase formation in T. reesei is enigmatic, however. Previous results from our laboratory raised the hypothesis that intermediates from the two galactose catabolic pathway may give rise to the accumulation of intracellular oligogalactosides that could act as inducer. Here we have therefore used high-performance anion-exchange chromatography-mass spectrometry to study the intracellular galactoglycome of T. reesei during growth on lactose, in T. reesei mutants impaired in galactose catabolism, and in strains with different cellulase productivities. Lactose, allo-lactose, and lactulose were detected in the highest amounts in all strains, and two trisaccharides (Gal-β-1,6-Gal-β-1,4-Glc/Fru and Gal-β-1,4-Gal-β-1,4-Glc/ Fru) also accumulated to significant levels. Glucose and galactose, as well as four further oligosaccharides (Gal-β-1,3/1,4/1,6-Gal; Gal-β-1,2-Glc) were only detected in minor amounts. In addition, one unknown disaccharide (Hex-β-1,1-Hex) and four trisaccharides were also detected. The accumulation of the unknown hexose disaccharide was shown to correlate with cellulase formation in the improved mutant strains as well as the galactose pathway mutants, and Gal-β-1,4-Gal-β-1,4-Glc/Fru and two other unknown hexose trisaccharides correlated with cellulase production only in the pathway mutants, suggesting that these compounds could be involved in cellulase induction by lactose. The nature of these oligosaccharides, however, suggests their formation by transglycosylation rather than by glycosyltransferases. Based on our results, the obligate nature of both galactose catabolic pathways for this induction must have another biochemical basis than providing substrates for inducer formation.

Original languageEnglish
Pages (from-to)5447-5456
Number of pages10
JournalApplied Microbiology and Biotechnology
Volume97
Issue number12
DOIs
Publication statusPublished - Jun 1 2013

Keywords

  • Cellulase
  • Galactoglycome
  • HPAEC-MS
  • Lactose
  • Trichoderma reesei

ASJC Scopus subject areas

  • Biotechnology
  • Applied Microbiology and Biotechnology

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    Karaffa, L., Coulier, L., Fekete, E., Overkamp, K. M., Druzhinina, I. S., Mikus, M., Seiboth, B., Novák, L., Punt, P. J., & Kubicek, C. P. (2013). The intracellular galactoglycome in Trichoderma reesei during growth on lactose. Applied Microbiology and Biotechnology, 97(12), 5447-5456. https://doi.org/10.1007/s00253-012-4667-y