Schematic of purification procedures. A One-Step bait fishing. A Hbt.salinarum strain overexpressing the bait protein fused to CBD is cultured in synthetic medium containing 13C6-leucine. The corresponding bait-control strain overexpressing the bait protein without CBD is cultured in synthetic medium containing 12C6-leucine. The lysate from both strains is mixed and purification done on one cellulose column. B Two-Step bait fishing. The bait overexpression strain and a general CBD-control strain expressing plain CBD are grown in complex medium. The bait-CBD fusion and the plain CBD are bound to separate cellulose columns and stringently washed to remove all proteins except bait or CBD. The columns are incubated with lysate from Hbt.salinarum cells grown in synthetic medium containing 12C-leucine (bait) or 13C-leucine (pMS4), respectively. After elution, the eluates are pooled.