Genetic identification of three ABC transporters as essential elements fornitrate respiration in Haloferax volcanii

More than 40 nitrate respiration-deficient mutants of Haloferax volcanii be longing to three different phenotypic classes were isolated. All 15 mutants of the null phenotype were complemented with a genomic library of the wild type Wild-type copies of mutated genes were recovered from complemented mu tants using two different approaches. The DNA sequences of 13 isolated frag ments were determined. Five fragments were found to overlap; therefore nine different genomic regions containing genes essential for nitrate respirati on could be identified. Three genomic regions containing genes coding for s ubunits of ABC transporters were further characterized. In two cases, genes coding for an ATP-binding subunit and a permease subunit were clustered an d overlapped by four nucleotides. The third gene for a permease subunit had no additional ABC transporter gene in proximity. One ABC transporter was f ound to be glucose specific. The mutant reveals that the ABC transporter so lely mediates anaerobic glucose transport. Based on sequence similarity, th e second ABC transporter is proposed to be molybdate specific, explaining i ts essential role in nitrate respiration. The third ABC transporter is prop osed to be anion specific. Genome sequencing has shown that ABC transporter s are widespread in Archaea. Nevertheless, this study represents only the s econd example of a functional characterization.