title: Characterization of a second physiologically relevant lactose permease gene (lacpB) in Aspergillus nidulans.
abstract: In Aspergillus nidulans, uptake rather than hydrolysis is the rate-limiting step of lactose catabolism. Deletion of the lactose permease A-encoding gene (lacpA) reduces the growth rate on lactose, while its overexpression enables faster growth than wild-type strains are capable of. We have identified a second physiologically relevant lactose transporter, LacpB. Glycerol-grown mycelia from mutants deleted for lacpB appear to take up only minute amounts of lactose during the first 60 h after a medium transfer, while mycelia of double lacpA/lacpB-deletant strains are unable to produce new biomass from lactose. Although transcription of both lacp genes was strongly induced by lactose, their inducer profiles differ markedly. lacpA but not lacpB expression was high in d-galactose cultures. However, lacpB responded strongly also to β-linked glucopyranose dimers cellobiose and sophorose, while these inducers of the cellulolytic system did not provoke any lacpA response. Nevertheless, lacpB transcript was induced to higher levels on cellobiose in strains that lack the lacpA gene than in a wild-type background. Indeed, cellobiose uptake was faster and biomass formation accelerated in lacpA deletants. In contrast, in lacpB knockout strains, growth rate and cellobiose uptake were considerably reduced relative to wild-type, indicating that the cellulose and lactose catabolic systems employ common elements. Nevertheless, our permease mutants still grew on cellobiose, which suggests that its uptake in A. nidulans prominently involves hitherto unknown transport systems.
authors.affiliation: Department of Biochemical Engineering, Faculty of Science and Technology, University of Debrecen, H-4032, Egyetem tér 1, Debrecen, Hungary.
authors.forename: Erzsébet
authors.initials: E
authors.lastname: Fekete
authors.affiliation: Department of Biochemical Engineering, Faculty of Science and Technology, University of Debrecen, H-4032, Egyetem tér 1, Debrecen, Hungary.
authors.forename: Anita
authors.initials: A
authors.lastname: Orosz
authors.affiliation: Department of Biochemical Engineering, Faculty of Science and Technology, University of Debrecen, H-4032, Egyetem tér 1, Debrecen, Hungary.
authors.forename: László
authors.initials: L
authors.lastname: Kulcsár
authors.affiliation: Department of Biochemical Engineering, Faculty of Science and Technology, University of Debrecen, H-4032, Egyetem tér 1, Debrecen, Hungary.
authors.forename: Napsugár
authors.initials: N
authors.lastname: Kavalecz
authors.affiliation: Department of Biochemical Engineering, Faculty of Science and Technology, University of Debrecen, H-4032, Egyetem tér 1, Debrecen, Hungary.
authors.forename: Michel
authors.initials: M
authors.lastname: Flipphi
authors.affiliation: Department of Biochemical Engineering, Faculty of Science and Technology, University of Debrecen, H-4032, Egyetem tér 1, Debrecen, Hungary.
authors.forename: Levente
authors.initials: L
authors.lastname: Karaffa
mesh_terms: D001233:Aspergillus nidulans / Q000235:genetics* / Q000378:metabolism*; D001692:Biological Transport / Q000235:genetics; D002475:Cellobiose / Q000378:metabolism; D005690:Galactose / Q000378:metabolism; D017353:Gene Deletion; D015966:Gene Expression Regulation, Fungal / Q000235:genetics*; D055786:Gene Knockout Techniques; D005936:Glucans / Q000378:metabolism; D005990:Glycerol / Q000378:metabolism; D007785:Lactose / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics*
chemical_list: D005936:Glucans; D026901:Membrane Transport Proteins; D002475:Cellobiose; C021499:lactose permease; D007785:Lactose; D005990:Glycerol; D005690:Galactose; C003328:sophorose