# Cyanobacteria as Chassis for Industrial Biotechnology: Progress and Prospects
## 2 Cyanobacterial \"Omics\"  
The model organism _Synechocystis_ sp. PCC 6803 (hereafter _Synechocystis_ 6803) in 1996 was the first photosynthetic organism to have its genome sequenced [53]. Advances in sequencing technologies and the decrease in their costs have led to more and more strains of cyanobacteria being fully sequenced [54; 55]. To date, CyanoBase ([[http://genome.microbed.jp/cyanobase](http://genome.microbed.jp/cyanobase)]([http://genome.microbed.jp/cyanobase](http://genome.microbed.jp/cyanobase))), one of the most widely used databases for cyanobacterial strains, contains 39 completed cyanobacterial genome sequences while the National Centre for Biotechnological Information (NCBI) ([[http://www.ncbi.nlm.nih.gov](http://www.ncbi.nlm.nih.gov)]([http://www.ncbi.nlm.nih.gov](http://www.ncbi.nlm.nih.gov))) contains 111 sequenced strains. The availability of these genomes has a huge impact on the directed molecular biology work that can be carried out. Genomic sequences can be used to identify pathways useful for the production of biotechnology relevant compounds. For example, a comparison between the genomic sequences of alkane-producing and non-producing cyanobacteria has led to the identification of the alkane-producing pathway [56]. Microarray data measures the level of expression of a large number of genes within a genome. There is a large amount of microarray data for _Synechocystis_ 6803 looking at levels of gene expression in different conditions that can be found in the databases Gene Expression Omnibus (GEO) [57], ArrayExpress [58] and Kyoto Encyclopedia of Genes and Genomes (KEGG) [59]. Although a lot of microarray data is on the two main model species, _Synechocystis_ 6803 and _Synechococcus elongatus_ PCC7942, there is also data on other cyanobacteria on the GEO database such as _Prochlorococcus marinus_ MED4 and _Nostoc punctiforme_ PCC73102. Recently, RNA-sequencing has started being used to study the transcriptome of cyanobacteria. For instance, RNA-sequencing transcriptomic  
Figure 1: Schematic overview of different biotechnological uses and potential products of genetically engineered cyanobacteria. Items under “Photosynthetic system” refer to native products that are directly linked to the functions within the thylakoid membrane. The photosynthetic system diverges electrons from two primary reactions in the thylakoids directly to H\({}_{2}\). The products of the Calvin cycle (carbohydrates, proteins, lipids and fatty acids) lead to the formation of various biofuel options. The white arrow indicates products under light conditions, while the black arrow indicates products under dark conditions. Items under “Biomass” refer to uses of the entire biomass and heterogeneous products through genetic engineering. PHA’s: Polyhydroxyalkanoateates, PUFA: Polyunsaturated fatty acids, BTL: bipolar tetraether lipids. All the arrows indicate the relative utilization or production of an item. The double ended arrow between “Biomass” and “Photosynthetic system” implies that biomass is a result of the photosynthetic system. analysis of the diazotrophic _Anabaena_ sp. strain 90 revealed the upregulation of phosphorous transport and assimilation genes (_pho_ regulon) during phosphorous deprivation in algal blooms [60]. RNA-sequencing was used to identify genes in _Synechocystis_ 6803 that could be engineered to make ethanol-resistant strains [61]. In another study, RNA-sequencing transcriptomic analysis revealed a gene encoding a phosphatase protein (_slr1860_) that promoted ethanol tolerance in _Synechocystis_ 6803 [62]. Metabolomics, transcriptomics and proteomics have been used to improve biofuel tolerances in _Synechocystis_ 6803, which provided valuable correlations between genes, protein expression and production titers of different biotechnological products [63; 64]. In a study on isoprene production from _Synechocystis_ 6803, the metabolomic and transcriptomic profiles were analysed under metabolic stress [64].