Incorporation and modification of fatty acids in cyanobacterial natural products biosynthesis.

Fatty acid-derived alkyl chains are often found in natural products, where they can exert a number of different functions, most notably biological membrane interactions. Such alkyl chains are difficult to modify regio- and stereoselectively, since most positions are distant from any directing functional group. Chemical and biochemical diversification of these moieties is therefore a challenge, and most organisms do not modify alkyl moieties to a great extent. Still, one particular group of microorgansims - cyanobacteria - display not only a large number of fatty acid-incorporating natural products, but also modify these to a great extent. Here, we provide an overview of the unique fatty acid metabolism of cyanobacteria in the context of natural products biosynthesis. We cover the diverse range of fatty acid incorporation mechanisms that these organisms use to recruit and commit fatty acids to natural products biosynthetic pathways. A variety of alkyl chain decorations and modifications that are found in cyanobacterial natural products are highlighted, illustrating the rich enzymatic arsenal that these organisms have evolved to diversify fatty acid-derived alkyl chains.

Discovery of Cyanobacterial Natural Products Containing Fatty Acid Residues*.

In recent years, extensive sequencing and annotation of bacterial genomes has revealed an unexpectedly large number of secondary metabolite biosynthetic gene clusters whose products are yet to be discovered. For example, cyanobacterial genomes contain a variety of gene clusters that likely incorporate fatty acid derived moieties, but for most cases we lack the knowledge and tools to effectively predict or detect the encoded natural products. Here, we exploit the apparent absence of a functional ß-oxidation pathway in cyanobacteria to achieve efficient stable-isotope-labeling of their fatty acid derived lipidome. We show that supplementation of cyanobacterial cultures with deuterated fatty acids can be used to easily detect natural product signatures in individual strains. The utility of this strategy is demonstrated in two cultured cyanobacteria by uncovering analogues of the multidrug-resistance reverting hapalosin, and novel, cytotoxic, lactylate-nocuolin A hybrids-the nocuolactylates.

Biosynthesis of Chlorinated Lactylates in Sphaerospermopsis sp. LEGE 00249.

Lactylates are an important group of molecules in the food and cosmetic industries. A series of natural halogenated 1-lactylates, chlorosphaerolactylates (1-4), were recently reported from Sphaerospermopsis sp. LEGE 00249. Here, we identify the cly biosynthetic gene cluster, containing all the necessary functionalities for the biosynthesis of the natural lactylates, based on in silico analyses. Using a combination of stable isotope incorporation experiments and bioinformatic analysis, we propose that dodecanoic acid and pyruvate are the key building blocks in the biosynthesis of 1-4. We additionally report minor analogues of these molecules with varying alkyl chains. This work paves the way to accessing industrially relevant lactylates through pathway engineering.