Photoheterotrophic growth of unicellular cyanobacterium Synechocystis sp. PCC 6803 gtr- dependent on fructose

Although cyanobacteria have specialized for a photolithoautotrophic mode of life during evolution many cyanobacterial strains have been identified as being capable of photoheterotrophy or even chemoheterotrophy. The mutant strain of Synechocystis sp. PCC 6803, which lacks the gtr gene coding for the strain's glucose/fructose permease, has been believed to be a strict photolithoautotroph in the past as it has lost the wild type's facility to use external glucose for both photoheterotrophy and light-induced chemoheterotrophy. However, recent experiments revealed the strain's capacity to use fructose for mixotrophic and photoheterotrophic growth, a sugar which is toxic for the wild type. Both the growth rate and the amount of fructose incorporated into the cells increased along with the fructose concentrations in the surrounding medium. Furthermore an increase of the total carbon mass of the cells within a liquid culture over a period of photoheterotrophic growth could be demonstrated. Contrary to the wild type, glucose could not be used for photoheterotrophic growth, and chemoheterotrophic growth failed with fructose as well as with glucose. [GRAPHICS] .