Identification and characterisation of hydrophobins from Fusarium graminearum

Fungal infection of barley and malt, particularly by strains of the genus Fusarium, is known to be a direct cause of undesirable beer gushing. Gushing is a phenomenon in which beer spontaneously, without agitation, vigorously over foams out from the package immediately on opening. We have shown previously that small fungal proteins called hydrophobins act as the gushing factors of beer. Hydrophobins have been found on the cell walls of hyphae and on spore surfaces, but they can also be secreted into the culture medium. The characteristic feature of these surface-active proteins is their ability to self-assemble at hydrophilic/hydrophobic interfaces forming amphipathic membranes. Based on sequence comparison, hydrophobins are divided into two different classes, I and II. The aim of our work was to isolate and characterise hydrophobins from a gushing active fungus Fusarium graminearum. We generated profile hidden Markov models (profile HMMs) for the hydrophobin classes IA, IB and II from the multiple sequence alignments of their known members. We searched Fusarium graminearum genome database of predicted proteins (http://www.broad.mit.edu) with the models. The best matching sequences and the corresponding genes were isolated and characterised. One of the putative hydrophobin genes was expressed in Trichoderma reesei and the hydrophobin-like protein was isolated from the culture filtrate of the transformant. A concentration of 0.1 ppm of the RP-HPLC purified protein was observed to induce beer gushing.