Abstract
The model cyanobacterium Synechocystis sp. PCC 6803 is the subject of studies investigating photosynthesis, genomics, nutrient cycling, and recently genetic engineering for the production of high-value compounds. Using cyanobacteria to produce compounds of high value to humanity is an area that has the potential to help the world in countless ways. In order to do this, genomes need to be created which remain stable throughout cell growth. A process that is hindering the production of biotechnology strains is genetic instability which involves mutations resulting in strains with altered phenotypes.
In the non-photosynthetic microorganism, E. coli increased genome stability has been achieved through the deletion of a core recombination protein encoded by recA. Thus, the idea of targeting DNA genes to overcome instability in cyanobacteria has come to light. This study investigates the role of genes: mutS1 (the encoded protein functions by identifying SNP mutations), mutS2 (encodes a protein associated with homologous recombination), recG (encodes a protein that functions in resuming stalled replication forks), and recN (encodes a protein which functions by protecting and repairing double-strand DNA breaks) in the Otago-University wild type strain (GT-O1) and a consistently reverting unstable Photosystem II mutant that cannot grow in pH 7.5 medium (ΔPsbO:ΔPsbU strain). Additionally, the instability mechanism in an unstable Photosystem II mutant strain that has reverted and restored photoautotrophic growth at pH7.5 is explored (ΔCyanoQ:ΔPsbV strain). This report shows the disruption of the genes mutS1, recN, and recG in the GT-O1 background led to a variation of responses to different intensities and wavelengths of light (especially UV-B light), as well as an increase in genomic instability of the ΔPsbO:ΔPsbU Photosystem II mutant when recN or mutS1 was disrupted. Preliminary data from the ΔCyanoQ:ΔPsbV pseudo revertant strain revealed a SNP mutation that enabled a photosynthetic thioredoxin protein to change its function allowing for growth under the stressful conditions of pH 7.5 medium. Results from this study indicate the leading candidate gene is mutS1 which should next be overexpressed as it could make cells more efficient at removing SNP mutations.