Evaluating Light-Induced Promoters for the Control of Heterologous Gene Expression in Synechocystis sp. PCC 6803

Cyanobacteria are enticing microbial factories, but little is understood how their gene control elements respond to the periodic availability to light. This research tested the capability of P-psbAII to control gene expression during light/dark conditions when moved to a neutral location within the Synechocystis sp. PCC 6803 genome. When the eYFP reporter gene was run by P-psbAII in the promoter's native genomic location, mutants exposed to 12-hour light conditions experienced a 15.8X increase in transcript abundance over that observed from the same construct exposed to 12-hour dark conditions. When this same construct was moved to the hypothetical coding region slr0168 in the genome, transcripts generated during 12 hour light conditions accumulated to 1.67X of the levels of transcripts generated by the same construct during 12 hour dark conditions. Three additional promoter constructs, P-psbAIII, P-groEL2, and P-sigD were also tested for differential expression in light and dark conditions within the neutral region slr0168. While low amounts of transcript accumulation were observed from P-groEL2 and P-sigD, the P-psbAIII construct accumulated 5.79X more transcripts when compared to transcript abundance during dark conditions, which highlights the potential of this promoter to control gene expression during diel-cycle light conditions. Additionally, nucleotide mutations were made to regions within P-psbAII. Mutations to the cis-acting hexo-nucleotide region increased expression 3.71X over that of the native promoter, while the addition of the HLR nucleotide region to the P-psbAII::Delta Hex construct increased expression 2.76X over that of the native promoter. (C) 2016 American Institute of Chemical Engineers