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 (F BPase-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. (199 8) Biochim. Biophys. Acta 1383: 232]. We now demonstrate that disruption of the gene encoding FBPase-II (fbp-II) with a kanamycin resistance gene cart ridge does not affect cell growth, Chi content, or CO2 assimilation in Syne chococcus PCC 7942, and disruption of the gene encoding FBPase-I (fbp-1) is a lethal mutation in both cyanobacteria. Accordingly, it is clear that FBP ase-I is necessary to sustain photosynthesis and gluconeogenesis in cyanoba cteria.