Differential effects of amino acid analogs on growth and heterocyst differentiation in two nitrogen-fixing blue-green algae

Abstract

Effects of a few amino acid analogs on growth and heterocyst differentiation have been studied in two nitrogen-fixing species ofAnabaena. All the analogs except α-methyl-DL-aspartic acid inhibited growth. Exposure of Anabaena doliolum, to DL-5-fluorotryptophan and DL-p-fluorophenylalanine caused pronounced fragmentation of filaments into single cells. At low concentrations (0.01 mM), α -methyl-DL-aspartic acid stimulated growth of the strain of A. doliolum as well as the strain of the second (unidentified) Anabaena species. Ethionine, DL-p-fluorophenylalanine, DL-5-fluorotryptophan, and canavanine blocked heterocyst differentiation, whereas α -methyl-DL-aspartic acid, a-methyl-DL-methionine, N-o-nitrophenylsulfenyl-l-tryptophan, nor leucine, and S-2-aminoethyl-l-cysteine did not show any significant effect. Treatment with 7-azatryptophan, DL-β-hydroxynorvaline,l-methionine-DL-sulfoximine, L-methionine sulfone, and β-2-thienyl-DL-alanine led to a twofold increase in heterocyst frequency. Possible modes of action of the analogs in growth inhibition and changes in heterocyst frequency are discussed.