Gene transfer to the desiccation-tolerant cyanobacterium Chroococcidiopsis

The coccoid cyanobacterium Chroococcidiopsis dominates microbial communitie s in the most extreme arid hot and cold deserts. These communities withstan d constraints that result from multiple cycles of drying and wetting and/or prolonged desiccation, through mechanisms which remain poorly understood. Here we describe the first system for genetic manipulation of Chroococcidio psis, Plasmids pDUCA7 and pRL489, based on the pDU1 replicon of Nostoc sp. strain PCC 7524, were transferred to different isolates of Chroococcidiopsi s via conjugation and electroporation. This report provides the first evide nce that pDU1 replicons can be maintained in cyanobacteria other than Nosto c and Anabaena. Following conjugation, both plasmids replicated in Chroococ cidiopsis sp. strains 029, 057, and 123 but not in strains 171 and 584, Bot h plasmids were electroporated into strains 029 and 123 but not into strain s 057, 171, and 584. Expression of P-psbA-luxAB on pRL489 was visualized th rough in vivo luminescence. Efficiencies of conjugative transfer for pDUCA7 and pRL489 into Chroococcidiopsis sp. strain 029 were approximately 10(-2) and 10(-4) transconjugants per recipient cell, respec tively. Conjugative transfer occurred with a lower efficiency into strains 057 and 123, Electro transformation efficiencies of about 10(-4) electrotransformants per recipi ent cell were achieved with strains 029 and 123, using either pDUCA7 or pRL 489. Extracellular deoxyribonucleases were associated with each of the five strains. Phylogenetic analysis, based upon the V6 to V8 variable regions o f 16S rRNA, suggests that desert strains 057, 123, 171, and 029 are distinc t from the type species strain Chroococcidiopsis thermalis PCC 7203. The hi gh efficiency of conjugative transfer of Chroococcidiopsis sp. strain 029, from the Negev Desert, Israel, makes this a suitable experimental strain fo r genetic studies on desiccation tolerance.