Bacteriohopanepolyol

Several studies have suggested that bacteriohopanepolyols play a role in the structure of membranes due to their polycylic structures and amphiphilic properties.{{Cite journal | vauthors = Tanaka Y |date= January 1993 |title=Agroactive Compounds of Microbial Origin |journal=Annual Review of Microbiology |volume=47 |issue=1 |pages=57–87 |doi=10.1146/annurev.micro.47.1.57 |pmid= 8257109 |issn=0066-4227}}{{cite journal | vauthors = Ourisson G, Rohmer M, Poralla K | title = Prokaryotic hopanoids and other polyterpenoid sterol surrogates | journal = Annual Review of Microbiology | volume = 41 | pages = 301–333 | date = 1987 | pmid = 3120639 | doi = 10.1146/annurev.mi.41.100187.001505 }} BHPs have been hypothesized to be an evolutionary precursor to sterols, a class of biochemical compounds which is primarily present in eukaryotic cell membranes.{{Cite journal | vauthors = Rohmer M, Bouvier-Nave P, Ourisson G |date= May 1984 |title=Distribution of Hopanoid Triterpenes in Prokaryotes |journal=Microbiology |language=en |volume=130 |issue=5 |pages=1137–1150 |doi=10.1099/00221287-130-5-1137 |doi-access= free |issn=1350-0872}} The presence of BHPs in membranes has been found to improve the temperature,{{cite journal | vauthors = Doughty DM, Coleman ML, Hunter RC, Sessions AL, Summons RE, Newman DK | title = The RND-family transporter, HpnN, is required for hopanoid localization to the outer membrane of Rhodopseudomonas palustris TIE-1 | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 108 | issue = 45 | pages = E1045–E1051 | date = November 2011 | pmid = 21873238 | pmc = 3215060 | doi = 10.1073/pnas.1104209108 | doi-access = free }} antimicrobial resistance, and pH tolerance {{cite journal | vauthors = Schmerk CL, Bernards MA, Valvano MA | title = Hopanoid production is required for low-pH tolerance, antimicrobial resistance, and motility in Burkholderia cenocepacia | journal = Journal of Bacteriology | volume = 193 | issue = 23 | pages = 6712–6723 | date = December 2011 | pmid = 21965564 | pmc = 3232912 | doi = 10.1128/JB.05979-11 }} of bacteria.

Additionally, BHPs have been found to be an important constituent of 'lipid rafts', which are enriched in specific lipids and provide transport, protein synthesis, and signal transduction proteins. Prior to their discovery in bacteria, lipid rafts were considered a key piece of the evolution of more complex, eukaryotic cells. {{cite journal | vauthors = Bramkamp M, Lopez D | title = Exploring the existence of lipid rafts in bacteria | journal = Microbiology and Molecular Biology Reviews | volume = 79 | issue = 1 | pages = 81–100 | date = March 2015 | pmid = 25652542 | pmc = 4342107 | doi = 10.1128/MMBR.00036-14 }}

Bacteriohopanepolyols have been found to be present in all types of sediment since their discovery in 1979,{{cite journal | vauthors = Pearson A, Flood Page SR, Jorgenson TL, Fischer WW, Higgins MB | title = Novel hopanoid cyclases from the environment | journal = Environmental Microbiology | volume = 9 | issue = 9 | pages = 2175–2188 | date = September 2007 | pmid = 17686016 | doi = 10.1111/j.1462-2920.2007.01331.x | bibcode = 2007EnvMi...9.2175P | url = https://resolver.caltech.edu/CaltechAUTHORS:20091116-092735268 }}{{Cite journal | vauthors = Ourissen G |date=1979 |title=The Hopanoids: palaeochemistry and biochemistry of a group of natural products |journal=Pure Appl. Chem. |volume=51 |issue=4 |pages=709–729 | doi = 10.1351/pac197951040709 |s2cid=20809792 }} and are produced by a wide range of bacteria including alpha-, beta-, cyano-, and gammaproteobacteria{{Cite journal | vauthors = Talbot HM, Summons RE, Jahnke LL, Cockell CS, Rohmer M, Farrimond P |date= February 2008 |title=Cyanobacterial bacteriohopanepolyol signatures from cultures and natural environmental settings |journal=Organic Geochemistry |language=en |volume=39 |issue=2 |pages=232–263 |doi=10.1016/j.orggeochem.2007.08.006|bibcode= 2008OrGeo..39..232T }} While early studies estimated that around half of all species of bacteria produce hopanoids, more recent studies estimate around 4% of bacteria have the ability to produce hopanoids.{{cite journal | vauthors = Pearson A, Rusch DB | title = Distribution of microbial terpenoid lipid cyclases in the global ocean metagenome | journal = The ISME Journal | volume = 3 | issue = 3 | pages = 352–363 | date = March 2009 | pmid = 19037261 | doi = 10.1038/ismej.2008.116 | bibcode = 2009ISMEJ...3..352P | doi-access = free }}

Several studies have used culture-independent methods to survey bacterial genomes for genes which may imply the ability to produce BHPs{{cite journal | vauthors = Welander PV, Summons RE | title = Discovery, taxonomic distribution, and phenotypic characterization of a gene required for 3-methylhopanoid production | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 109 | issue = 32 | pages = 12905–12910 | date = August 2012 | pmid = 22826256 | pmc = 3420191 | doi = 10.1073/pnas.1208255109 | doi-access = free | bibcode = 2012PNAS..10912905W }} The squalene-hopene cyclase gene (sqhC) produces an enzyme that catalyzes the cyclization of squalene, a precursor of BHPs. Among thirty sequenced bacteria, this gene was found in the genomes of all hopanoid-containing bacteria, and very few of the bacteria which do not produce hopanoids, and therefore the presence of the sqhC gene was assumed to mean that the gene was expressed. Overall, fewer than ten-percent of the marine and freshwater bacterioplankton were found to possess this gene.

Bacteriohopanepolyols are commonly identified through chemical extraction of organic matter followed by analysis on a mass spectrometer.{{Cite journal | vauthors = Kusch S, Rush D |date= October 2022 |title=Revisiting the precursors of the most abundant natural products on Earth: A look back at 30+ years of bacteriohopanepolyol (BHP) research and ahead to new frontiers |journal=Organic Geochemistry |language=en |volume=172 |pages=104469 |doi=10.1016/j.orggeochem.2022.104469|bibcode= 2022OrGeo.17204469K |url= https://www.vliz.be/imisdocs/publications/93/381093.pdf }} Extraction protocols are intended to purify natural samples to allow for analysis of a simpler mixture of compounds. Differences in the efficiency of extraction methods have been found to vary for different types of BHPs.{{Cite journal | vauthors = Herrmann |date=1996-01-15 |title=A non-extractable triterpenoid of the hopane series in Acetobacter xylinum |journal=FEMS Microbiology Letters |volume=135 |issue=2–3 |pages=323–326 |doi=10.1016/0378-1097(95)00473-4 |issn=0378-1097}}{{Cite journal | vauthors = Berndmeyer C, Thiel V, Blumenberg M |date= April 2014 |title=Test of microwave, ultrasound and Bligh & Dyer extraction for quantitative extraction of bacteriohopanepolyols (BHPs) from marine sediments |journal=Organic Geochemistry |volume=68 |pages=90–94 |doi=10.1016/j.orggeochem.2014.01.003 |bibcode= 2014OrGeo..68...90B |issn=0146-6380}}

BHPs were first analyzed using a gas chromatograph mass spectrometer (GC-MS),{{Cite journal | vauthors = Depmeier W, Schmid H, Haenssler F |date= September 1980 |title=PdB2O4, the first palladium borate |journal=Naturwissenschaften |language=en |volume=67 |issue=9 |pages=456 |doi=10.1007/BF00405642 |issn=0028-1042}} however the use of HPLC-MS methods have become more common in recent years due to the ability to analyze BHPs without the Rohmer preparation procedure which resulted in a loss of specificity. Despite its advantages, analysis of BHPs using HPLC-MS is complicated by a lack of sufficient standards and variations in the efficiency of acetylation among different BHPs.

The polycyclic hydrocarbon skeleton of BHPs makes them resistant to degradation, and allows for them to be preserved for long periods of time in the geologic record. However, the use of BHPs as a biomarker for a specific group of bacteria is limited by the current state of knowledge regarding the identification of groups of bacteria which produce specific bacteriohopanepolyols. Some BHPs may be produced by a diverse range of organisms, such as bacteriohopane-32,33,34,35-tetrol (BHT), and the biological source of many BHPs is uncertain, complicating interpretation of BHPs.

Initially, BHPs were thought to only be present in aerobic bacteria,{{Cite journal | vauthors = Talbot HM, Watson DF, Pearson EJ, Farrimond P |date= October 2003 |title=Diverse biohopanoid compositions of non-marine sediments |journal=Organic Geochemistry |language=en |volume=34 |issue=10 |pages=1353–1371 |doi=10.1016/S0146-6380(03)00159-1|bibcode= 2003OrGeo..34.1353T }} however they have since been found in anaerobic bacteria.{{cite journal | vauthors = Blumenberg M, Krüger M, Nauhaus K, Talbot HM, Oppermann BI, Seifert R, Pape T, Michaelis W | title = Biosynthesis of hopanoids by sulfate-reducing bacteria (genus Desulfovibrio) | journal = Environmental Microbiology | volume = 8 | issue = 7 | pages = 1220–1227 | date = July 2006 | pmid = 16817930 | doi = 10.1111/j.1462-2920.2006.01014.x | bibcode = 2006EnvMi...8.1220B }}{{Cite journal | vauthors = Sáenz JP, Wakeham SG, Eglinton TI, Summons RE |date= December 2011 |title=New constraints on the provenance of hopanoids in the marine geologic record: Bacteriohopanepolyols in marine suboxic and anoxic environments |journal=Organic Geochemistry |language=en |volume=42 |issue=11 |pages=1351–1362 |doi=10.1016/j.orggeochem.2011.08.016|bibcode= 2011OrGeo..42.1351S }} BHPs have often been used as an indicator for cyanobacteria,{{cite journal | vauthors = Summons RE, Jahnke LL, Hope JM, Logan GA | title = 2-Methylhopanoids as biomarkers for cyanobacterial oxygenic photosynthesis | journal = Nature | volume = 400 | issue = 6744 | pages = 554–557 | date = August 1999 | pmid = 10448856 | doi = 10.1038/23005 | bibcode = 1999Natur.400..554S }} and forty-nine out of fifty-eight cultured cyanobacteria have been found to produce BHP. In particular, 2β-methylbiohopanoids has only been found to be produced in significant quantities by cyanobacteria.

An isomer of bacteriohopanetetrol was found to be associated with anoxic and suboxic conditions in marine pelagic sediments. Bacteriohopanepolyol identification has been paired with stable carbon isotope analysis, for greater specificity. In particular, the detection of 3-methylhopanoids (hopanoids with a methyl group at the C3 position) which are highly depleted in ¹³C are interpreted as a proxy for methanotrophy.

{{Reflist}}

• Hopane

Category:Terpenes and terpenoids