Nordic cyanobacterial and algal lipids: Triacylglycerol accumulation, chemotaxonomy and bioindustrial potential

Abstract

The ability to capture and convert sunlight, water and nutrients into useful compounds make photosynthetic microbes ideal candidates for the bio-industrial factories of the future. However, the suitability of isolates from temperate regions to grow under Nordic conditions is questionable. In this work, we explore the chemotaxonomy of Nordic strains of cyanobacteria and one green alga and evaluate their potential as raw materials for the production of lipid-based bio-industrial compounds. Thin-layer chromatography was used to identify the presence of triacylglycerol, which were detected in the majority of strains. Fatty acid methyl ester profiles were analysed to determine the suitability of strains for the production of biodiesel or the production of polyunsaturated fatty acids for the nutraceutical industry. The Nordic Synechococcus strains were unique in demonstrating fatty acid profiles comprised mostly C14:0, C16:0 and C16:1 and lacking polyunsaturated fatty acids. These properties translated to superior predicted biodiesel qualities, including cetane number, cold filter plugging point and oxidative stability compared to the other evaluated strains. Polyunsaturated fatty acids were detected at high levels (38-53%), with Calothrix sp. 336/3 being abundant in two essential fatty acids, linoleic and alpha-linolenic acid (21 and 17%, respectively). Gamma-linoleic acid was the predominant polyunsaturated fatty acid for the remaining strains (13-21%). In addition to assessing the potential of Nordic strains for bio-industrial production, this work also discusses issues such as taxonomy and predictive modelling, which can affect the identification of prospective highperforming strains. | INTRODUCTIONCyanobacteria and green algae are oxygenic photosynthetic microorganisms able to adapt to and flourish in a diversity of environments.They utilise many protective mechanisms, such as lipid unsaturation, to adjust to changing environments. Lipids, being major components of membranes, play a key role in protecting the photosynthetic machinery against environmental stresses such as strong light, salt, and extremes in temperature (Los et al., 2013). The Nordic region is generally characterised by low temperatures, with long, dark winters contrasting short, bright summers (Ferro et al., 2020). Using strains adapted to such unique conditions may be advantageous in the pursuit of robust algal production systems (Cheregi et al., 2019). Indeed, Long-chain polyunsaturated fatty acids (PUFAs) have been found to Anita Santana-S anchez and Fiona Lynch contributed equally to this study.

slr2103, a homolog of type-2 diacylglycerol acyltransferase genes, for plastoquinone-related neutral lipid synthesis and NaCl-stress acclimatization in a cyanobacterium, Synechocystis sp. PCC 6803

“…PCC 7942), Microcystis aeruginosa, and Oscillatoria rubescenes, contained no TG and/or accumulated very little TG under nitrogen (N)-starved conditions, which is a well-known stressor to induce TG accumulation in algal species (e.g., Piorreck et al, 1984). In contrast, TG was reported to be found in some other cyanobacterial strains, including Nostoc commune and Arthrospira platensis (formally known as Spirulina platensis) (Taranto et al, 1993;Ramadan et al, 2008;Peramuna and Summers, 2014;Santana-Sańchez et al, 2021). However, TG was identified through TLC analysis only, with noncyanobacterial phospholipids such as phosphatidylcholine and phophatidylethanolamine also being extracted in substantial amounts in some cases, leaving the possibility of contamination by some other organism(s) that intrinsically contain TG.…”

Incorporation, fate, and turnover of free fatty acids in cyanobacteria

“…Based on these recent findings, the authors raise the question to the actual presence of TAG in Synechocystis 6803 (Mori-Moriyama et al 2023 ). In 2021, eight cold climate-adapted cyanobacterial strains (including both filamentous and unicellular strains) were screened for the presence of TAGs, from which six were found to contain it (Santana-Sánchez et al 2021 ). Interestingly, the two strains that did not show detectable TAGs belong to the Synechococcus genus, but a third strain of the same genus was found to contain them (Santana-Sánchez et al 2021 ).…”

“…In 2021, eight cold climate-adapted cyanobacterial strains (including both filamentous and unicellular strains) were screened for the presence of TAGs, from which six were found to contain it (Santana-Sánchez et al 2021 ). Interestingly, the two strains that did not show detectable TAGs belong to the Synechococcus genus, but a third strain of the same genus was found to contain them (Santana-Sánchez et al 2021 ). Usually, accumulation of storage lipids depends on exogenous sources of acyl chains, rather than de novo FASII (Cronan and Thomas 2009 ).…”

Acyl plastoquinol is a major substance that co-migrates with triacylglycerol in cyanobacteria

“…A cyanobacterial acyltransferase Slr2103, a homolog of PES1, was reported to synthesize TAG rather than phytyl esters (Aizouq et al 2020). This study was believed to open a new study of cyanobacterial TAG (Santana-Sánchez et al 2021). However, many researchers have already noticed that the data in Aizouq et al (2020) were strange.…”