| A transposon, Tn7, interruption library was used to create random genetic mutations in Synechocystis sp. PCC 6803 whose genome has about 1,500 genes with unknown functions. Three hypothetical genes disrupted by Tn7 were selected owing to their altered growth characteristics and physiological functions were investigated.;A mutant that showed a higher growth rate and increased poly-3-hydroxybutyrate content than wild type under high osmotic pressure led to the identification of ssr1765. More ssr1765-containing transcript was observed in wild type exposed to high osmotic pressure, indicating the up-regulation of ssr1765 activity under such conditions. The data suggested that ssr1765 is involved in poly-3-hydroxybutyrate biosynthesis by controlling the flow of carbon and reducing power to it. Increased poly-3-hydroxybutyrate content increased the ability of cells to cope with high osmotic pressure. Increased PSII activity indicated by increased oxygen evolution in ssr1765 mutant possibly provided the reducing power and carbon needed for PHB biosynthesis and resulted in a more reduced PQ pool.;The inactivation of sll1434 resulted in impaired photoautotrophic growth when exposed to high osmotic pressure. sll1434 encodes a probable penicillin-binding protein that plays a key role in finalizing the peptidoglycan layer by crosslinking the adjacent peptides in the cell wall. Electron microscopy images showed an aberrant peptidoglycan layer in the mutant. Gas chromatography/mass spectrometry data indicated that more glucosylglycerol than wild type was present in the medium in which the mutant was grown. A faster uptake of a fluorescent dye was observed in the mutant and indicated increased cell envelope permeability. Sll1434 appears to be involved in peptidoglycan biosynthesis.;Synechocystis sp. PCC 6803 cells use photosynthesis to convert solar energy to chemical energy and to fix carbon via the Calvin cycle. In an effort to study the assembly and stabilization of photosystem I, a mutant in slr1552 was identified with impaired photoautotrophic growth. The mutant had less chlorophyll, a lower oxygen evolution rate and fewer photosystem I complexes compared to wild type. slr1552 is proposed to encode a putative transmembrane protein that may be involved in the assembly or stabilization of photosystem I. |
