Partial recovery of light-independent chlorophyll biosynthesis in the chlL-deletion mutant of Synechocystis sp. PCC 6803.

A chlL-deletion mutant of Synechocystis sp. PCC 6803 designated as chlL- was unable to make significant amounts of chlorophyll in darkness. However, an apparent pseudorevertant has been generated spontaneously that can synthesize an increased amount of chlorophyll under light-activated heterotrophic growth conditions. Under these conditions, the chlorophyll content in this pseudorevertant was about 20% of that in the wild-type strain and about 4 times more than that in the original and in the recently recreated chlL-deletion mutant. This is paralleled by increased performance of dark-grown cells in terms of chlorophyll fluorescence induction and oxygen evolution rates in the pseudorevertant versus in the original mutant. PCR analysis confirmed that the chlL- -pseudorevertant mutant still lacked the chlL gene. These results imply that the light-independent chlorophyll biosynthesis pathway was partly recovered.