Abstract
The model organism Synechocystis sp. PCC 6803 (hereafter Synechocystis 6803) has been used for photosynthetic, genomic, proteomic and transcriptomic studies. Recent discoveries of genetic instability in lab strains throughout the world led to the resequencing of the lab strain used in the University of Otago named GT-O1. This lead to the discovery of its substrain GT-O2 that possesses five mutations that were unique from the GT-O1 strain. These mutations were in the chlH, hik8, fadD, htrA and yvcK genes. The GT-O2 strain was unable to acclimatise to prolonged high light periods in comparison to the GT-O1 strain. To elucidate the cause of the high light phenotype, chlH mutant strains (made in the GT-O1 and GT-O2 background) and hik8 mutant strains (made in the GT-O1 background) had been constructed to express either the GT-O1 or GT-O2 copy of the gene of interest. No major high light phenotype was detected in the chlH mutant strains with the exception of a GT-O2 background mutant strain expressing the GT-O1 copy of chlH. This mutant unexpectedly demonstrated severe growth deficiency despite expressing a non-mutated copy of chlH. This suggested the chlH mutation was not solely responsible for the GT-O2 high light phenotype observed but rather a combination of GT-O2 mutations. Under high light, the hik8 mutant strains had shown no differences in growth rates regardless of the copy of hik8 expressed; the hik8 gene was therefore ruled out due to the lack of phenotype. This leaves the fadD, htrA and yvcK genes as the other potential contributors to the high light phenotype. Mutants had been made in a similar fashion to the chlH mutants for the fadD, htrA and yvcK genes in this study. Results from this study demonstrated that the fadD, htrA and yvcK genes were able to confer photoprotection through different mechanisms; the fadD gene affects chl a production and may affect membrane stability; the htrA gene may confer photoprotection through protease activity; the yvcK gene affects carbon metabolism which would upset the balance between photosynthesis and respiration. Along with the chlH and hik8 gene, it paints a picture that all five mutations in GT-O2 strain all contribute to its high light phenotype. Data suggests that the mutations likely occurred to allow the GT-O2 strain to adapt better on a heterotrophic media that it is maintained on. However, these mutations proved disadvantageous in conditions where photoautotrophic growth is required and this would be further exacerbated under high light.