Terminal Olefin Profiles and Phylogenetic Analyses of Olefin Synthases of Diverse Cyanobacterial Species

Abstract

Cyanobacteria can synthesize alkanes and alkenes, which are considered to be infrastructure-compatible biofuels. In terms of physiological function, cyanobacterial hydrocarbons are thought to be essential for membrane flexibility for cell division, size, and growth. The genetic basis for the biosynthesis of terminal olefins (1-alkenes) is a modular type I polyketide synthase (PKS) termed olefin synthase (Ols). The modular architectures of Ols and structural characteristics of alkenes have been investigated only in a few species of the small percentage (approximately 10%) of cyanobacteria that harbor putative Ols pathways. In this study, investigations of the domains, modular architectures, and phylogenies of Ols in 28 cyanobacterial strains suggested distinctive pathway evolution. Structural feature analyses revealed 1-alkenes with three carbon chain lengths (C, C, and C). In addition, the total cellular fatty acid profile revealed the diversity of the carbon chain lengths, while the fatty acid feeding assay indicated substrate carbon chain length specificity of cyanobacterial Ols enzymes. Finally, analyses suggested that the N terminus of the modular Ols enzyme exhibited characteristics typical of a fatty acyl-adenylate ligase (FAAL), suggesting a mechanism of fatty acid activation via the formation of acyl-adenylates. Our results shed new light on the diversity of cyanobacterial terminal olefins and a mechanism for substrate activation in the biosynthesis of these olefins. Cyanobacterial terminal olefins are hydrocarbons with promising applications as advanced biofuels. Despite the basic understanding of the genetic basis of olefin biosynthesis, the structural diversity and phylogeny of the key modular olefin synthase (Ols) have been poorly explored. An overview of the chemical structural traits of terminal olefins in cyanobacteria is provided in this study. In addition, we demonstrated by fatty acid feeding assays that cyanobacterial Ols enzymes might exhibit substrate carbon chain length specificity. Furthermore, by performing bioinformatic analyses, we observed that the substrate activation domain of Ols exhibited features typical of a fatty acyl-adenylate ligase (FAAL), which activates fatty acids by converting them to fatty acyl-adenylates. Our results provide further insight into the chemical structures of terminal olefins and further elucidate the mechanism of substrate activation for terminal olefin biosynthesis in cyanobacteria.

Comparative Genomics Discloses the Uniqueness and the Biosynthetic Potential of the Marine Cyanobacterium Hyella patelloides

“…Furthermore, the BGC involved in the production of a terminal olefin, belongs to the CF-8 cluster family previously described (Calteau et al, 2014). The terminal olefin synthase (OLS pathway) is one of the two biosynthetic pathways that produce hydrocarbons from fatty acids identified in cyanobacteria (Mendez-Perez et al, 2011;Coates et al, 2014;Zhu et al, 2018). This pathway is composed by a large type I PKS with modular organization that includes the following domains organization: Fatty acyl-AMP ligase (FAAL), acyl carrier protein (ACP), ketosynthase (KS), acyltransferase (AT), ketoreductase (KR), ACP2, sulfotransferase (ST) and thioesterase (TE) (Mendez-Perez et al, 2011;Coates et al, 2014;Zhu et al, 2018).…”

“…The terminal olefin synthase (OLS pathway) is one of the two biosynthetic pathways that produce hydrocarbons from fatty acids identified in cyanobacteria (Mendez-Perez et al, 2011;Coates et al, 2014;Zhu et al, 2018). This pathway is composed by a large type I PKS with modular organization that includes the following domains organization: Fatty acyl-AMP ligase (FAAL), acyl carrier protein (ACP), ketosynthase (KS), acyltransferase (AT), ketoreductase (KR), ACP2, sulfotransferase (ST) and thioesterase (TE) (Mendez-Perez et al, 2011;Coates et al, 2014;Zhu et al, 2018). There is the indication that cyanobacterial strains harboring this pathway produced more hydrocarbons than those possessing the alternative one (Coates et al, 2014).…”

Insights Into Limnothrix sp. Metabolism Based on Comparative Genomics

“…A closer look at contig MRBY01000033 from the latter revealed a beta-ketoacyl synthase (NIES208_12590) that has the same domains when compared to OLS PKS modules that were presented by Coates et al (2014) . A recent study also reported the presence of an OLS pathway in Limnothrix rosea IAM M-220 using bioinformatic analyses ( Zhu et al, 2018 ).…”

“…The MEP (methylerythritol-phosphate) pathway, which uses glyceraldehyde 3-phosphate and pyruvate to synthesize terpenoids ( Pattanaik and Lindberg, 2015 ), is present in all four Limnothrix . Additionally, the CACIAM 69d, P13C2 and PR1529 strains are capable of producing hydrocarbons from fatty acids using the AAR/ADO (acyl-ACP reductase/aldehyde-deformylating oxygenase) pathway, while Limnothrix rosea IAM M-220 appears to achieve the same using the OLS (α-olefin synthase) pathway ( Zhu et al, 2018 ), which involves the participation of PKS modules ( Coates et al, 2014 ).…”

Photosynthetic Conversion of Carbon Dioxide to Oleochemicals by Cyanobacteria: Recent Advances and Future Perspectives

“…With the carbon chain lengths ranging from C15 to 19, cyanobacterial alk(a/e)nes could be directly used in diesel and jet engines, and have attracted great attention from academics. On the one hand, chemical structures and profiles of cyanobacterial alk(a/e)nes were examined across a wide range of cyanobacterial species (Liu et al, 2013;Coates et al, 2014;Zhu et al, 2018). On the other hand, several model cyanobacterial species were metabolically engineered for improving their alk(a/e)nes production (Mendez-Perez et al, 2011;Hu et al, 2013;Wang et al, 2013;Kageyama et al, 2015;Peramuna et al, 2015) (Table 1).…”