[2] Isolation and genetic characterization of pseudorevertants from site-directed PSI mutants in Synechocystis 6803

Publisher Summary Synechocystis 6803 is a model organism for the study of oxygenic photosynthesis. Its genome has recently been sequenced, and it is naturally competent and can be easily transformed. It also has an active homologous recombination mechanism. This chapter describes a procedure for isolating spontaneous pseudorevertants from PSI mutants of Synechocystis 6803, localization and identification of the suppressor mutations, and some of the properties of the genetic transformation system in this cyanobacterium. Photoautotrophic and mixotrophic growth under white light was used to isolate and characterize pseudorevertants. Isolates obtained from one selective condition were tested for their ability to grow in other conditions by streaking on plates. Three classes of pseudorevertants have been found: those capable of growth under (1) photoautotrophic conditions, but not mixotrophic conditions; (2) mixotrophic conditions, but not photoautotrophic conditions; and (3) both conditions. Pseudorevertants generally grow more slowly than wild-type under these conditions.