AMINO-ACID-TRANSPORT IN TAXONOMICALLY DIVERSE CYANOBACTERIA AND IDENTIFICATION OF 2 GENES ENCODING ELEMENTS OF A NEUTRAL AMINO-ACID PERMEASE PUTATIVELY INVOLVED IN RECAPTURE OF LEAKED HYDROPHOBIC AMINO-ACIDS

The activities of uptake of thirteen C-14-labeled amino acids were det ermined in nine cyanobacteria, including the unicellular strains Synec hococcus sp, strain PCC 7942 and Synechocystis sp, strain PCC 6803; th e filamentous strain Pseudanabaena sp, strain PCC 6903, and the filame ntous, heterocyst-forming strains Anabaena sp, strains PCC 7120 and PC C 7937; Nostoc sp. strains PCC 7413 and PCC 7107; Calothrix sp, strain PCC 7601 (which is a mutant unable to develop heterocysts); and Fisch erella muscicola UTEX 1829, Amino acid transport mutants, selected as mutants resistant to some amino acid analogs, were isolated from the A nabaena, Nostoc, Calothrix, and Pseudanabaena strains. All of the test ed cyanobacteria bear at least a neutral amino acid transport system, and some strains also bear transport systems specific for basic or aci dic amino acids. Two genes, natA and natB, encoding elements (conserve d component, NatA, and periplasmic binding protein, NatB) of an ABC-ty pe permease for neutral amino acids were identified by insertional mut agenesis of strain PCC 6803 open reading frames from the recently publ ished genomic DNA sequence of this cyanobacterium. DNA sequences homol ogous to natA and natB from strain PCC 6803 were detected by hybridiza tion in eight cyanobacterial strains tested, Mutants unable to transpo rt neutral amino acids, including natA and natB insertional mutants, a ccumulated in the extracellular medium a set of amino acids that alway s included Ala, Val, Phe, lie, and Leu, A general role for a cyanobact erial neutral amino acid permease in recapture of hydrophobic amino ac ids leaked from the cells is suggested.