[13] Conjugal transfer of plasmids to cyanobacteria

This chapter discusses the conjugal transfer of plasmids to cyanobacteria. The chapter mentions different types of cyanobacteria—the filamentous, heterocyst-forming cyanobacteria—that include the genera Anabaena and Nostoc, which are of particular interest as they are capable of oxygenic photosynthesis, aerobic nitrogen fixation, and cellular differentiation with associated pattern formation. A complete understanding of the unique capabilities of cyanobacteria depends upon the development of systems for their genetic analysis. Some unicellular cyanobacteria are transformable but not reproducible. Such vectors can introduce (1) the wild-type homologs of mutant alleles for complementation analysis; (2) the transposons for mutagenesis;(3) cloned and altered genes for site-specific mutation; and (4) genes with an easily assayed product, such as/3-galactosidase or luciferase, to permit study of transcriptional control. The chapter describes techniques that have been used to construct shuttle vectors for the strains of Anabaena and Nostoc and conditions for conjugal transfer of those vectors from  Escherichia coli  to cyanobacterial hosts. The colonies of cyanobacteria growing on antibiotic-containing medium are streaked on the same selective medium used in mating.