Specific cellobionic acid transporter NCU05853 (CBT-1). a Accumulation of cellobionic acid (A2) in the supernatant of β-glucosidase and NCU05853 mutant strains, providing Avicel as carbon source. Δ3BG, triple β-glucosidase deletion strain; Δ3BGΔ5853, triple β-glucosidase deletion plus ΔNCU05853 deletion strain. b Percentage of the remaining sugars after incubation with S. cerevisiae strains expressing different transporters. c Homology model of CBT-1, showing the conserved arginine residue R438. G2 cellobiose, X2 xylobiose, A2 cellobionic acid.