sp. strain ATCC 29133 (PCC 73102; 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 29133. By use of a Tn derivative, Tn-1063 (Km Bm Sm), delivered by conjugation from , antibiotic-resistant mutants of 29133 were generated at a frequency of approximately 1 × 10, 0.4% of which expressed a nitrogen fixation (heterocyst) defective phenotype. Mutant strain UCD 328 was isolated after co-culture of 86 29133::Tn-1063 clones with the symbiotic plant partner, ; 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 29133, and the transposition site identified from a 29133 genomic library. Transposon mutagenesis has thus provided the means for isolation and identification of developmental and symbiotic-specific genes of 29133.


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