FIG. 1.

Construction of a microaerobically expressed hydrogenase system in R. leguminosarum bv. viciae UPM791. The σ⁵⁴-dependent promoter of hupSL expressed in symbiosis (top) was replaced by the FnrN-dependent PfixN promoter from R. leguminosarum UPM791. This construct was introduced into the pK18 mobsac plasmid, producing pKPF1. This plasmid was used to exchange the PhupSL promoter in strain UPM791 and in cosmid pAL618, obtaining strain SPF25 and cosmid pALPF1, respectively. Arrows, genes flanking the PhupSL promoter and the fixNOQP genes; white and grey boxes (top), σ⁵⁴ and integration host factor binding sequences in PhupSL; bottom box, FnrN consensus binding site (anaerobox). B, BamHI; E, EcoRI; N, NdeI; X, XbaI.