Abstract
Cyanobacteria are known as rich repositories of natural products. One cyanobacterial-microbial consortium (isolate HT-58-2) is known to produce two fundamentally new classes of natural products: the tetrapyrrole pigments tolyporphins A–R, and the diterpenoid compounds tolypodiol, 6-deoxytolypodiol, and 11-hydroxytolypodiol. The genome (7.85 Mbp) of the Nostocales cyanobacterium HT-58-2 was annotated previously for tetrapyrrole biosynthesis genes, which led to the identification of a putative biosynthetic gene cluster (BGC) for tolyporphins. Here, bioinformatics tools have been employed to annotate the genome more broadly in an effort to identify pathways for the biosynthesis of tolypodiols as well as other natural products. A putative BGC (15 genes) for tolypodiols has been identified. Four BGCs have been identified for the biosynthesis of other natural products. Two BGCs related to nitrogen fixation may be relevant, given the association of nitrogen stress with production of tolyporphins. The results point to the rich biosynthetic capacity of the HT-58-2 cyanobacterium beyond the production of tolyporphins and tolypodiols.
Highlights
Tolyporphins represent a class of compounds in the pigments of life family with structural features distinct from other prominent constituents, including heme, chlorophylls, bacteriochlorophylls, cobalamin, and coenzyme F430
The natural products include tolypodiol (Figure 3), the first diterpenoid compound obtained from cyanobacteria [13]
We report an evaluation of genes that support the biosynthesis of tolypodiols as well as other natural products, deepening the coding potential survey of the genome that was initially reported [9]
Summary
Tolyporphins represent a class of compounds in the pigments of life family with structural features distinct from other prominent constituents, including heme, chlorophylls, bacteriochlorophylls, cobalamin, and coenzyme F430. The structural diversity suggests an in vivo role for tolyporphins as secondary metabolites in as-yet undefined defense processes. If so, this represents a fundamentally new biological function in the pigments of life family. Scrutiny of the lipophilic extracts of the HT-58-2 culture has revealed other new natural products. The natural products include tolypodiol (Figure 3), the first diterpenoid compound obtained from cyanobacteria [13]. Prior work [9] annotating the genome of the Nostocales HT-58-2 suggested numerous genes for diverse functions, but did not delve deeply into the BGCs of natural products, including those for tolypodiols. Scrutiny of the lipophilic extracts of the HT-58-2 culture has revealed other new natFFiigguurree33..SSttrruucctutuurrraeeloopfftrtoolldyypupocodtdsii.oolTlaahnneddnttwwatoouarananalallopogrguouedessuiicssotosllaaittneedcdlfufrrdoomemtccoyylaaynnpooobbdaacicotteelrri(iaaFllisgstturraariienn3HH)T,T--t55h88e--22f..irst diterpenoid compound obtained from cyanobacteria [13]. The issue arises as to the biosynthetic capacity of HT-58-2, i.e., what other natural products might be produced either under normal or stressed conditions?
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