Transposon mutagenesis of Nostoc sp. strain ATCC 29133, a filamentous cyanobacterium with multiple cellular differentiation alternatives

Section of Microbiology, Division of Biological Sciences, University of California, Davis, CA 95616, USA ABSTRACT Nostoc sp. strain ATCC 29133 (PCC 73102; Nostoc 29133) is a symbiotically-competent, facultatively heterotrophic, diazotrophic cyanobacterium with the capacity to differentiate specialized cells such as heterocysts, akinetes and hormogonial filaments. We have optimized several methods for physiological and molecular genetic analysis of Nostoc 29133. By use of a Tn 5 derivative, Tn 5 -1063 (Km r Bm r Sm r ), delivered by conjugation from Escherichia coli , antibiotic-resistant mutants of Nostoc 29133 were generated at a frequency of approximately 1 x 10 -6 , 0.4% of which expressed a nitrogen fixation (heterocyst) defective phenotype. Mutant strain UCD 328 was isolated after co-culture of 86 Nostoc 29133::Tn 5 -1063 clones with the symbiotic plant partner, Anthoceros punctatus ; strain UCD 328 expressed a symbiotic phenotype of increased frequency of hormogonia-dependent infection. The transposon and flanking genomic DNA was recovered from strain UCD 328, the mutation and phenotype reconstructed by homologous recombination in Nostoc 29133, and the transposition site identified from a Nostoc 29133 genomic library. Transposon mutagenesis has thus provided the means for isolation and identification of developmental and symbiotic-specific genes of Nostoc 29133. Author for correspondence: J. C. Meeks. Tel: +1 916 752 3346. Fax: +1 916 752 9014. Keywords: Nostoc sp. ATCC 29133, diazotrophic cyanobacterium, symbiotic cyanobacterium, transposon mutagenesis, homologous recombination