A Deletion of a Putative Glucosyl Transferase Increases Carotenoids Production in Synechocystis sp. PCC 6803

Abstract

Aim: Deletion the putative glucosyl transferase (Slr1125) in order to investigate its relationship with the unique carotenoid glycoside myxoxanthophyll. Methodology: In Synechocystis sp. PCC 6803, slr1125 ORF was replaced by streptomycin resistance cassette. The resulted homologous mutant strain was analyzed by high pressure liquid chromatography and electron microscope in order to assess the impact of the gene deletion on myxoxanthophyll and the cell wall ultrastructure of the Δslr1125S strain. Results: In the Δslr1125S mutant strain, myxoxanthophyll and chlorophyll decreased and photomixotrophic growth was very poor at a low light intensity of 0.5 µE m-2 s-1. However, at higher light intensity myxoxanthophyll accumulates in the mutant reach (1120ng/ml/OD730) that is 5-fold higher than that of wild type strain. Photosynthetic pigments increased in the mutant strain and growth improved at a light intensity of 100µE m-2 s-1. In addition, a pool of novel carotenoids accumulated part of which are precursor intermediates of myxoxanthophyll biosynthetic pathway. Cell wall dysfunction observed during cell growth in liquid and on plate and verified by ultrastructure deformation of the cell wall layers. S-layer disappeared and peptidoglycan was poorly developed. Conclusion: The putative glucosyl transferase (Slr1125) plays an important role in cell wall biogenesis of the unicellular cyanobacterium Synechocystis sp. PCC 6803 that is indirectly affecting the carotenoid biosynthetic pathway specially the glycosylated carotenoid myxoxanthophyll. Indeed, these results highlight the notion that cross talk and interconnectedness between cellular processes exist that is critical for metabolic engineering designs.