Induction of extracellular β-galactosidase (Bga1) formation by D-galactose in Hypocrea jecorina is mediated by galactitol

Erzsébet Fekete, Lavente Karaffa, Christian P. Kubicek, Attila Szentirmai, Bernhard Seiboth

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

The ability of Hypocrea jecorina (Trichoderma reesei) to grow on lactose strongly depends on the formation of an extracellular glycoside hydrolase (GH) family 35 β-galactosidase, encoded by the bga1 gene. Previous studies, using batch or transfer cultures of pregrown cells, had shown that bga 1 is induced by lactose and D-galactose, but to a lesser extent by galactitol. To test whether the induction level is influenced by the different growth rates attainable on these carbon sources, bga 1 expression was compared in carbon-limited chemostat cultivations at defined dilution (=specific growth) rates. The data showed that bga1 expression by lactose, D-galactose and galactitol positively correlated with the dilution rate, and that galactitol and D-galactose induced the highest activities of β-galactosidase at comparable growth rates. To know more about the actual inducer for β-galactosidase formation, its expression in H. jecorina strains impaired in the first steps of the two D-galactose-degrading pathways was compared. Induction by D-galactose and galactitol was still found in strains deleted in the galactokinase-encoding gene gal1, which is responsible for the first step of the Leloir pathway of D-galactose catabolism. However, in a strain deleted in the aldose/D-xylose reductase gene xyl1, which performs the reduction of D-galactose to galactitol in a recently identified second pathway, induction by D-galactose, but not by galactitol, was impaired. On the other hand, induction by D-galactose and galactitol was not affected in an L-arabinitol 4-dehydrogenase (lad1)-deleted strain which is impaired in the subsequent step of galactitol degradation. These results indicate that galactitol is the actual inducer of Bga 1 formation during growth on D-galactose in H. jecorina.

Original languageEnglish
Pages (from-to)507-512
Number of pages6
JournalMicrobiology
Volume153
Issue number2
DOIs
Publication statusPublished - Feb 1 2007

    Fingerprint

ASJC Scopus subject areas

  • Microbiology

Cite this