PORIN FROM THE HALOPHILIC SPECIES ECTOTHIORHODOSPIRA-VACUOLATA - CLONING, STRUCTURE OF THE GENE AND COMPARISON WITH OTHER PORINS

The gene coding for the anion-specific porin of the halophilic eubacte rium Ectothiorhodospira (Ect.) vacuolata was cloned and sequenced, the first such gene so analyzed from a purple sulfur bacterium. It encode s a precursor protein consisting of 374 amino acid (aa)-residues inclu ding a signal peptide of 22-aa residues. Comparison with aa sequences of porins from several other members of the Proteobacteria revealed li ttle homology. Only two regions showed local homology with the previou sly sequenced porins of Neisseria species, Comamonas acidovorans, Bord etella pertussis, Alcaligenes eutrophus, and Burkholderia cepacia. Gen omic Southern blot hybridization studies were carried out with a probe derived from the 5' end of the gene coding for the porin of Ect. vacu olata. Two related species, Ect. haloalkaliphila and Ect. shaposhnikov ii, exhibited a clear signal, while the extremely halophilic bacterium Halorhodospira (Hlr.) halophila (formerly Ect. halophila) did not sho w any cross-hybridization even at low stringency. This result is in go od accordance with a recently proposed reassignment within the family Ectothiorhodospiraceae, which included the separation of the extremely halophilic species into the new genus Halorhodospira. (C) 1997 Elsevi er Science B.V.