Functional Analysis of Fructose-1,6-Bisphosphatase Isozymes (fbp-I and fbp-II Gene Products) in Cyanobacteria

Synechococcus PCC 7942 contains two fructose-1,6-bisphosphatase isozymes (FBPase-I and FBPase-II), while Synechocystis PCC 6803 has only one (FBPase-I) in spite of the occurrence of two FBPase isozyme genes [Tamoi et al. (1998) Biochim. Biophys. Acta 1383: 232]. We now demonstrate that disruption of the gene encoding FBPase-II (fbp-II) with a kanamycin resistance gene cartridge does not affect cell growth, Chl content, or CO2 assimilation in Synechococcus PCC 7942, and disruption of the gene encoding FBPase-I (fbp-I) is a lethal mutation in both cyanobacteria. Accordingly, it is clear that FBPase-I is necessary to sustain photosynthesis and gluconeogenesis in cyanobacteria.