The rapid increase in worldwide population coupled with the increasing demand for fossil fuels has led to an increased urgency to develop sustainable sources of energy and chemicals from renewable resources. Using microorganisms to produce high-value chemicals and next-generation biofuels is one sustainable option and is the focus of much current research. Cyanobacteria are ideal platform organisms for chemical and biofuel production because they can be genetically engineered to produce a broad range of products directly from CO , H O, and sunlight, and require minimal nutrient inputs. The purpose of this review is to provide an overview on advances that have been or could be made to improve strains of cyanobacteria for industrial purposes. First, the benefits of using cyanobacteria as a platform for chemical and biofuel production are discussed. Next, an overview of cyanobacterial strain improvements by genetic engineering is provided. Finally, mutagenesis techniques to improve the industrial potential of cyanobacteria are described. Along with providing an overview on various areas of research that are currently being investigated to improve the industrial potential of cyanobacteria, this review aims to elucidate potential targets for future research involving cyanobacteria as an industrial microorganism. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1357-1371, 2016.

Cyanobacteria photosynthetically produce long-chain hydrocarbons, which are considered as infrastructure-compatible biofuels. However, native cyanobacteria do not produce these hydrocarbons at sufficient rates or yields to warrant commercial deployment. This research sought to identify specific genes required for photosynthetic production of alkanes to enable future metabolic engineering for commercially viable production of alkanes. The two putative genes (alr5283 and alr5284) required for long-chain hydrocarbon production in Anabaena sp. PCC 7120 were knocked out through a double crossover approach. The knockout mutant abolished the production of heptadecane (C17H36). The mutant is able to be complemented by a plasmid bearing the two genes along with their native promoters only. The complemented mutant restored photosynthetic production of heptadecane. This combined genetic and metabolite (alkanes) profiling approach may be broadly applicable to characterization of knockout mutants, using N2-fixing cyanobacteria as a cellular factory driven by solar energy to produce a wide range of commodity chemicals and drop-in-fuels from atmospheric gases (CO2 and N2 gas) and mineralized water.Electronic supplementary materialThe online version of this article (10.1186/s13568-018-0700-6) contains supplementary material, which is available to authorized users.

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1Some vegetative cells of Anabaena cylindrica are programed to differentiate semi-regularly spaced, 2 single heterocysts along filaments. Since heterocysts are terminally differentiated non-dividing 3 cells, with the sole known function for solar-powered N2-fixation, is it necessary for a heterocyst 4 to retain the entire genome (7.1 Mbp) from its progenitor vegetative cell? By sequencing the 5 heterocyst genome, we discovered and confirmed that at least six DNA elements (0.12 Mbp) are 6 deleted during heterocyst development. The six-element deletions led to the restoration of five 7 genes (nifH1, nifD, hupL, primase P4 and a hypothetical protein gene) that were interrupted in 8 vegetative cells. The deleted elements contained 172 genes present in the genome of vegetative 9 cells. By sequence alignments of intact nif genes (nifH, nifD and hupL) from N2-fixing 10 cyanobacteria (multicellular and unicellular) as well as other N2-fixing bacteria (non-11 cyanobacteria), we found that interrupted nif genes all contain the conserved core sequences that 12 may be required for phage DNA insertion. Here, we discuss the nif genes interruption which 13 uniquely occurs in heterocyst-forming cyanobacteria. To our best knowledge, this is first time to 14 sequence the genome of heterocyst, a specially differentiated oxic N2-fixing cell. This research 15 demonstrated that (1) different genomes may occur in distinct cell types in a multicellular 16 bacterium; and (2) genome editing is coupled to cellular differentiation and/or cellular function in 17 a heterocyst-forming cyanobacterium. 18 19 Keywords 20 cyanobacteria, heterocysts, oxic nitrogen fixation, genome editing, phage DNA insertion, 21 multicellular bacterium 22 Bioinformatics analysis. Reads trimming, assembly and mapping were carried out using CLC 132 Genomics Workbench 10.1.1 (Qiagen). Trimming was carried out using a Q of 20 as the cutoff, 133 eliminating any read with any ambiguous nucleotide and removing the 5 and 15 terminal 134 nucleotides in the 3' and 5' ends respectively. Assembly of the trimmed reads was accomplished 135 by setting an arbitrary minimum contig length of 3,000 bp and using the automated function to 136 select a word size of 23 and a bubble size of 50; finally, reads were mapped (mismatch cost: 2, 137 insertion cost: 3, deletion cost: 3, minimum length fraction: 0.5 and minimum similarity fraction:

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