Editing Steroid (section)

=== Prokaryotic ===

Although sterol biosynthesis is rare in prokaryotes, certain bacteria, including ''[[Methylococcus capsulatus]]'', specific [[methanotroph]]s, [[myxobacteria]], and the [[planctomycete]] ''[[Gemmata obscuriglobus]]'', are capable of producing sterols. In ''G. obscuriglobus'', sterols are essential for cell viability, but their roles in other bacteria remain poorly understood.<ref name="Franke_2021">{{cite book | vauthors = Franke JD | chapter = Sterol Biosynthetic Pathways and Their Function in Bacteria. | veditors = Villa TG, de Miguel Bouzas T | title = Developmental Biology in Prokaryotes and Lower Eukaryotes | date = 2021 | pages = 215-227 | doi = 10.1007/978-3-030-77595-7_9 | isbn = 978-3-030-77595-7 | location = Cham | publisher = Springer}}</ref> 

Prokaryotic sterol synthesis involves the tetracyclic steroid framework, as found in [[myxobacteria]],<ref name="pmid12519197">{{cite journal | vauthors = Bode HB, Zeggel B, Silakowski B, Wenzel SC, Reichenbach H, Müller R | title = Steroid biosynthesis in prokaryotes: identification of myxobacterial steroids and cloning of the first bacterial 2,3(S)-oxidosqualene cyclase from the myxobacterium Stigmatella aurantiaca | journal = Molecular Microbiology | volume = 47 | issue = 2 | pages = 471–81 | date = Jan 2003 | pmid = 12519197 | doi = 10.1046/j.1365-2958.2003.03309.x | s2cid = 37959511 | doi-access = }}</ref> as well as [[hopanoids]], pentacyclic lipids that regulate bacterial membrane functions.<ref name="pmid21531832">{{cite journal | vauthors = Siedenburg G, Jendrossek D | title = Squalene-hopene cyclases | journal = Applied and Environmental Microbiology | volume = 77 | issue = 12 | pages = 3905–15 | date = Jun 2011 | pmid = 21531832 | pmc = 3131620 | doi = 10.1128/AEM.00300-11 | bibcode = 2011ApEnM..77.3905S }}</ref> These sterol biosynthetic pathways may have originated in bacteria or been transferred from [[eukaryote]]s.<ref name="pmid20333205">{{cite journal | vauthors = Desmond E, Gribaldo S | title = Phylogenomics of sterol synthesis: insights into the origin, evolution, and diversity of a key eukaryotic feature | journal = Genome Biology and Evolution | volume = 1 | pages = 364–81 | year = 2009 | pmid = 20333205 | pmc = 2817430 | doi = 10.1093/gbe/evp036 }}</ref> 

Sterol synthesis depends on two key enzymes: [[squalene monooxygenase]] and [[oxidosqualene cyclase]]. Phylogenetic analyses of oxidosqualene cyclase (Osc) suggest that some bacterial Osc genes may have been acquired via [[horizontal gene transfer]] from eukaryotes, as certain bacterial Osc proteins closely resemble their eukaryotic homologs.<ref name="Franke_2021" />