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. 2016 Jun 24:7:990.
doi: 10.3389/fmicb.2016.00990. eCollection 2016.

Sterol Synthesis in Diverse Bacteria

Jeremy H Wei  1 , Xinchi Yin  1 , Paula V Welander  1
Affiliations

Sterol Synthesis in Diverse Bacteria

Jeremy H Wei et al. Front Microbiol. .

Abstract

Sterols are essential components of eukaryotic cells whose biosynthesis and function has been studied extensively. Sterols are also recognized as the diagenetic precursors of steranes preserved in sedimentary rocks where they can function as geological proxies for eukaryotic organisms and/or aerobic metabolisms and environments. However, production of these lipids is not restricted to the eukaryotic domain as a few bacterial species also synthesize sterols. Phylogenomic studies have identified genes encoding homologs of sterol biosynthesis proteins in the genomes of several additional species, indicating that sterol production may be more widespread in the bacterial domain than previously thought. Although the occurrence of sterol synthesis genes in a genome indicates the potential for sterol production, it provides neither conclusive evidence of sterol synthesis nor information about the composition and abundance of basic and modified sterols that are actually being produced. Here, we coupled bioinformatics with lipid analyses to investigate the scope of bacterial sterol production. We identified oxidosqualene cyclase (Osc), which catalyzes the initial cyclization of oxidosqualene to the basic sterol structure, in 34 bacterial genomes from five phyla (Bacteroidetes, Cyanobacteria, Planctomycetes, Proteobacteria, and Verrucomicrobia) and in 176 metagenomes. Our data indicate that bacterial sterol synthesis likely occurs in diverse organisms and environments and also provides evidence that there are as yet uncultured groups of bacterial sterol producers. Phylogenetic analysis of bacterial and eukaryotic Osc sequences confirmed a complex evolutionary history of sterol synthesis in this domain. Finally, we characterized the lipids produced by Osc-containing bacteria and found that we could generally predict the ability to synthesize sterols. However, predicting the final modified sterol based on our current knowledge of sterol synthesis was difficult. Some bacteria produced demethylated and saturated sterol products even though they lacked homologs of the eukaryotic proteins required for these modifications emphasizing that several aspects of bacterial sterol synthesis are still completely unknown.

Keywords: biomarkers; lipid biosynthesis; methanotrophs; myxobacteria; oxidosqualene cyclase; planctomycetes; squalene epoxidase; sterols.

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Figures

Figure 1
Figure 1
Sterol biosynthesis in eukaryotes. All sterol biosynthetic pathways begin with the oxidation of squalene to oxidosqualene and subsequent cyclization to lanosterol (vertebrates and fungi) or cycloartenol (plants). Shown are the initial enzymatic steps in the conversion of lanosterol to zymosterol which occurs similarly in vertebrates and fungi. Proteins involved in these steps have been characterized from a variety of eukaryotes and the locus to tags shown are those from Saccharomyces cerevisiae (Erg).
Figure 2
Figure 2
Mass spectra of sterols identified in this study. Spectra of the following acetylated sterols: cycloartenol (9,19-cyclolanost-24-en-3-ol), 4,4-dimethylcholesta-8,24-dien-3-ol, 4,4-dimethylcholesta-8-en-3-ol, 4-methylcholesta-8,24-dien-3-ol, 4-methylcholesta-8-en-3-ol. Spectra of the following trimethylsilylated sterols: lanosterol (lanosta-8,24-dien-3-ol) and zymosterol (cholesta-8,24-dien-3-ol).
Figure 3
Figure 3
Distribution of Osc protein sequences in metagenomes. Each bar represents the number of Osc homologs identified in the metagenomes from that ecosystem. The majority of homologs were found in freshwater, soil and marine metagenomes.
Figure 4
Figure 4
Maximum likelihood phylogenetic tree of oxidosqualene cyclase protein sequences from bacterial and eukaryotic isolate genomes. Bacterial squalene hopene cyclase (Shc) sequences were used as the outgroup. Eukaryotic lanosterol synthases (LAS) and bacterial Shc branches are collapsed for better visualization of the tree. Cycloartenol synthases are marked with a CAS following the strain name. Strain names without a CAS label are lanosterol synthase homologs. Colored branches represent different bacterial phyla: δ-Proteobacteria (blue), Cyanobacteria (green), Planctomycetes (cyan), γ-Proteobacteria (red), Bacteriodetes (pink), α-Proteobacteria (brown), and Verrucomicrobia (orange). Black branches represent eukaryotic sequences.
Figure 5
Figure 5
Maximum likelihood phylogenetic tree of bacterial and eukaryotic genomic and metagenomic Osc protein sequences. Red branches represent bacterial sequences and black branches are eukaryotic sequences. Blue labels indicate metagenomic sequences and black labels indicate sequences from genomes. Bacterial squalene hopene cyclases (Shc) sequences were used as the outgroup. Eukaryotic lanosterol synthases (LAS) and bacterial Shc branches are collapsed for better visualization of the tree. Cycloartenol synthases are marked with a CAS following the strain name. Strain names without a CAS label are lanosterol synthase homologs.
Figure 6
Figure 6
Sterols production in the myxobacteria. Extracted ion chromatograms (m/z 69, 440, 442, 454, 456, 468, and 498) of total lipid extract (TLE) from five myxobacteria. C. coralloides and C. fuscus TLEs were extracted from liquid cultures and were acetylated prior to running on the GC-MS. E. salina, P. pacifica, and S. amylolyticus TLEs were extracted from cultures on a plate as growing them in liquid cultures was difficult. These TLEs were trimethylsilylated prior to running on the GC-MS. Sterol peaks were identified based on their mass spectra as shown in Figure 2.
Figure 7
Figure 7
Amino acid alignments of the critical functional domains of oxidosqualene cyclase (A) and squalene epoxidase (B) homologs adapted from Fischer and Pearson (2007). Residues in black indicate residues that have been demonstrated to have a role in the biosynthesis of sterols in eukaryotes (Ruckenstuhl et al., ; Abe et al., ; Fischer and Pearson, 2007). Gray residues are those that differ from the conserved residue. In the Osc alignment, an isoleucine (I) at 453 (yellow) indicates a cycloartenol synthase and a valine (V) at 453 (blue) indicates a lanosterol synthase (Summons et al., 2006). Numbers correspond to residues in human Osc and SE. Bold labels indicate bacterial strains tested in this study. #: eukaryotic sequences, *: bacteria that have been shown to produce sterols.
Figure 8
Figure 8
Sterols production in the aerobic methanotrophs. Extracted ion chromatograms (m/z 69, 440, 442, 454, 456, 468, and 498) of total lipid extract (TLE) from four aerobic methanotrophs. All TLEs were extracted from liquid cultures and were acetylated prior to running on the GC-MS. Sterol peaks were identified based on their mass spectra as shown in Figure 2.
Figure 9
Figure 9
Sterols production in one Bacteriodetes and one α-Proteobacterium. Extracted ion chromatograms (m/z 69, 440, 442, 454, 456, 468, and 498) of total lipid extract (TLE) from the Bacteriodetes strains F. taffensis and the α-Proteobacterium M. caenitepidi. All TLEs were extracted from liquid cultures. The F. taffensis TLE was acetylated prior to running on the GC-MS. M. caenitepidi TLEs were trimethylsilylated prior to running on the GC-MS. Sterol peaks were identified based on their mass spectra as shown in Figure 2.
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References

    1. Abe I., Abe T., Lou W., Masuoka T., Noguchi H. (2007). Site-directed mutagenesis of conserved aromatic residues in rat squalene epoxidase. Biochem. Biophys. Res. Commun. 352, 259–263. 10.1016/j.bbrc.2006.11.014 - DOI - PubMed
    1. Alain K., Intertaglia L., Catala P., Lebaron P. (2008). Eudoraea adriatica gen. nov., sp. nov., a novel marine bacterium of the family Flavobacteriaceae. Int. J. Syst. Evol. Microbiol. 58, 2275–2281. 10.1099/ijs.0.65446-0 - DOI - PubMed
    1. Altschul S. F., Madden T. L., Schaffer A. A., Zhang J. H., Zhang Z., Miller W., et al. . (1997). Gapped BLAST and PSI-BLAST: a new generation of protein database search programs. Nucleic Acids Res. 25, 3389–3402. 10.1093/nar/25.17.3389 - DOI - PMC - PubMed
    1. Banta A. B., Wei J. H., Welander P. V. (2015). A distinct pathway for tetrahymanol synthesis in bacteria. Proc. Natl. Acad. Sci. U.S.A. 112, 13478–13483. 10.1073/pnas.1511482112 - DOI - PMC - PubMed
    1. Bard M., Bruner D. A., Pierson C. A., Lees N. D., Biermann B., Frye L., et al. . (1996). Cloning and characterization of ERG25, the Saccharomyces cerevisiae gene encoding C-4 sterol methyl oxidase. Proc. Natl. Acad. Sci. U.S.A. 93, 186–190. 10.1073/pnas.93.1.186 - DOI - PMC - PubMed

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