OBLIGATE PHOTOTROPHY IN CYANOBACTERIA - MORE THAN A LACK OF SUGAR-TRANSPORT

DNA hybridization using the Synechocystis PCC6803 glucose transporter gene, glcP, revealed a single homologous region in two facultative pho toautotrophic strains out of three tested, and none in three obligate autotrophs. In one of the latter, Synechococcus PCC7942, integration o f glcP into the chromosome resulted in glucose sensitivity. A subclone isolated as glucose-tolerant had lost glcP. Integration in a replicat ive vector allowed glucose transport and photoheterotrophic growth, bu t could not be maintained. Thus lack of sugar transport could explain cyanobacterial obligate autotrophy. However, at least in Synechococcus PCC7942, acquisition of such a transport capacity created a metabolic disequilibrium barely compatible with survival. (C) 1998 Federation o f European Microbiological Societies. Published by Elsevier Science B. V.