Editing Polyhydroxybutyrate

{{Short description|Polymer}}
[[File:Micrografia di cristalli sferulitici di poli(idrossi butirrato) (PHB).jpg|thumb|Polymeric crystals of PHB observed by polarizing optical microscope.]]

'''Polyhydroxybutyrate''' ('''PHB''') is a [[Polyhydroxyalkanoates|polyhydroxyalkanoate]] (PHA), a [[polymer]] belonging to the [[polyester]]s class that are of interest as bio-derived and [[biodegradable plastic]]s.<ref>{{cite book |doi=10.1002/14356007.n05_n07 |chapter=Carbohydrates as Organic Raw Materials |title=Ullmann's Encyclopedia of Industrial Chemistry |year=2010 |last1=Lichtenthaler |first1=Frieder W. |isbn=978-3-527-30673-2 }}</ref> The poly-3-hydroxybutyrate (P3HB) form of PHB is probably the most common type of polyhydroxyalkanoate, but other polymers of this class are produced by a variety of organisms: these include poly-4-hydroxybutyrate (P4HB), polyhydroxyvalerate (PHV), polyhydroxyhexanoate (PHH), polyhydroxyoctanoate (PHO) and their [[copolymer]]s.

==Biosynthesis==
PHB is produced by [[microorganisms]] (such as ''[[Cupriavidus necator]]'', ''[[Methylobacterium rhodesianum]]'' or ''[[Bacillus megaterium]]'') apparently in response to conditions of physiological stress;<ref name="AckermannMüller1995">{{cite journal |doi=10.1016/0168-1656(94)00138-3 |title=Methylobacterium rhodesianum cells tend to double the DNA content under growth limitations and accumulate PHB |journal=Journal of Biotechnology |volume=39 |issue=1 |pages=9–20 |year=1995 |last1=Ackermann |first1=Jörg-uwe |last2=Müller |first2=Susann |last3=Lösche |first3=Andreas |last4=Bley |first4=Thomas |last5=Babel |first5=Wolfgang }}</ref> mainly conditions in which nutrients are limited. The polymer is primarily a product of [[carbon]] assimilation (from [[glucose]] or [[starch]]) and is employed by microorganisms as a form of energy storage molecule to be metabolized when other common energy sources are not available. {{Citation needed|date=August 2019}}

Microbial biosynthesis of PHB starts with the [[Condensation reaction|condensation]] of two molecules of [[Coenzyme A|acetyl-CoA]] to give acetoacetyl-CoA which is subsequently reduced to hydroxybutyryl-CoA. This latter compound is then used as a monomer to polymerize PHB.<ref name="Biopolymers">{{cite book | last = Steinbüchel | first = Alexander | title = Biopolymers, 10 Volumes with Index | publisher = [[John Wiley & Sons|Wiley-VCH]] | year = 2002 | isbn = 978-3-527-30290-1}}{{page needed|date=May 2017}}</ref> PHAs granules are then recovered by disrupting the cells.<ref>{{cite journal |doi=10.1016/j.bej.2007.11.029 |title=Isolation and purification of bacterial poly(3-hydroxyalkanoates) |journal=Biochemical Engineering Journal |volume=39 |issue=1 |pages=15–27 |year=2008 |last1=Jacquel |first1=Nicolas |last2=Lo |first2=Chi-Wei |last3=Wei |first3=Yu-Hong |last4=Wu |first4=Ho-Shing |last5=Wang |first5=Shaw S. |bibcode=2008BioEJ..39...15J }}</ref>

[[Image:Poly-(R)-3-hydroxybutyrat.svg|thumb|right|200px|Structure of poly-(''R'')-3-hydroxybutyrate (P3HB), a '''polyhydroxyalkanoate''']]
[[Image:Polyhydroxyalkanoates.png|thumb|400px|right|Chemical structures of P3HB, PHV and their copolymer PHBV]]

==Thermoplastic polymer==
Most commercial plastics are synthetic polymers derived from [[petrochemical]]s. They tend to resist [[biodegradation]]. PHB-derived plastics are attractive because they are [[compost]]able and derived from renewables and are bio-degradable.

[[Imperial Chemical Industries|ICI]] had developed the material to [[pilot plant]] stage in the 1980s, but interest faded when it became clear that the cost of material was too high, and its properties could not match those of [[polypropylene]]. Some bottles were made for Wella's "Sanara" range of shampoo; an example using the tradename "Biopol" is in the collection of the [[Science Museum, London|Science Museum]], London.

In 1996, Monsanto (who sold PHB as a copolymer with PHV) bought all patents for making the polymer from ICI/Zeneca including the trademark "Biopol".<ref>{{Cite web |date=2013-03-28 |title=Trade Mark Details |url=https://www.ipo.gov.uk/trademark/history/GB50000000001202507.pdf |access-date=2024-12-30}}</ref> However, Monsanto's rights to Biopol were sold to the American company [[Metabolix]] in 2001 and Monsanto's fermenters producing PHB from bacteria were closed down at the start of 2004. Monsanto began to focus on producing PHB from plants instead of bacteria.<ref name=Poirier>{{cite journal |doi=10.1016/0141-8130(95)93511-U |pmid=7772565 |title=Synthesis of high-molecular-weight poly([r]-(-)-3-hydroxybutyrate) in transgenic Arabidopsis thaliana plant cells |journal=International Journal of Biological Macromolecules |volume=17 |issue=1 |pages=7–12 |year=1995 |last1=Poirier |first1=Yves |last2=Somerville |first2=Chris |last3=Schechtman |first3=Lee A. |last4=Satkowski |first4=Michael M. |last5=Noda |first5=Isao }}</ref> But now with so much media attention on GM crops, there has been little news of Monsanto's plans for PHB.<ref name="CouldEat">{{cite web |title=Plastics You Could Eat |url=http://www.firstscience.com/site/articles/sykes.asp |access-date=November 17, 2005 }}</ref>

Biopol is currently used in the medical industry for [[Surgical suture|internal suture]]. It is nontoxic and biodegradable, so it does not have to be removed after recovery.<ref>{{cite book |doi=10.1016/B978-0-12-396983-5.00001-6 |chapter=Polymer Synthesis and Processing |title=Natural and Synthetic Biomedical Polymers |pages=1–31 |year=2014 |last1=Kariduraganavar |first1=Mahadevappa Y. |last2=Kittur |first2=Arjumand A. |last3=Kamble |first3=Ravindra R. |isbn=9780123969835 }}</ref>

TephaFLEX is a bacterially derived poly-4-hydroxybutyrate, manufactured using a recombinant fermentation process by Tepha Medical Devices, intended for a variety of medical applications that require biodegradable materials such as [[Surgical_suture#Absorbability|absorbable sutures]].<ref>[https://www.tepha.com/technology/overview/ Tepha Medical Devices Technology Overview]</ref>

==Properties==
*Water-insoluble and relatively resistant to hydrolytic degradation. This differentiates PHB from most other currently available [[biodegradable plastic]]s, which are either water-soluble or moisture-sensitive.
*Good oxygen permeability.
*Good ultra-violet resistance but poor resistance to acids and bases.
*Soluble in chloroform and other chlorinated hydrocarbons.<ref>{{cite journal |id={{INIST|19110437}} |doi=10.1002/aic.11274 |title=Solubility of polyhydroxyalkanoates by experiment and thermodynamic correlations |journal=AIChE Journal |volume=53 |issue=10 |pages=2704–14 |year=2007 |last1=Jacquel |first1=Nicolas |last2=Lo |first2=Chi-Wei |last3=Wu |first3=Ho-Shing |last4=Wei |first4=Yu-Hong |last5=Wang |first5=Shaw S. |doi-access=free |bibcode=2007AIChE..53.2704J }}</ref>
*Biocompatible and hence is suitable for medical applications.
*Melting point 175&nbsp;°C., and glass transition temperature 2&nbsp;°C.
*Tensile strength 40 [[Pascal (unit)|MPa]], close to that of polypropylene.
*Sinks in water (while polypropylene floats), facilitating its anaerobic biodegradation in sediments.
*Non-toxic.
*Less 'sticky' when melted.

==History==
Polyhydroxybutyrate was first isolated and characterized in 1925 by French [[microbiologist]] [[Maurice Lemoigne]].<ref>{{cite journal |last1=Lemoigne |first1=M |year=1926 |title=Produits de dehydration et de polymerisation de l'acide ß-oxobutyrique |language=fr |trans-title=Dehydration and polymerization product of β-oxy butyric acid |journal=Bull. Soc. Chim. Biol. |volume=8 |pages=770–82 }}</ref>

==Biodegradation==

Firmicutes and proteobacteria can degrade PHB. ''Bacillus'', ''Pseudomonas'' and ''Streptomyces'' species can degrade PHB. ''[[Pseudomonas lemoigne]]'', [[Comamonas|''Comamonas'' sp.]] ''[[Acidovorax faecalis]]'', ''[[Aspergillus fumigatus]]'' and ''[[Variovorax paradoxus]]'' are soil microbes capable of degradation. ''[[Alcaligenes faecalis]]'', ''[[Pseudomonas]]'', and ''[[Illyobacter delafieldi]]'', are obtained from anaerobic sludge. ''[[Comamonas testosteroni]]'' and ''[[Pseudomonas stutzeri]]'' were obtained from sea water. Few of these are capable of degrading at higher temperatures; notably excepting thermophilic [[Streptomyces|''Streptomyces'' sp.]] and a thermophilic strain of [[Aspergillus|''Aspergillus'' sp.]]<ref>{{cite journal |doi=10.3390/ijms10093722 |pmid=19865515 |pmc=2769161 |title=Biodegradability of Plastics |journal=International Journal of Molecular Sciences |volume=10 |issue=9 |pages=3722–42 |year=2009 |last1=Tokiwa |first1=Yutaka |last2=Calabia |first2=Buenaventurada P. |last3=Ugwu |first3=Charles U. |last4=Aiba |first4=Seiichi |doi-access=free }}</ref>

==References==
<references/>

==External links==
* [http://www.epa.gov/greenchemistry/pubs/pgcc/winners/sba05.html Abstract of award for PHAs]

[[Category:Polyesters]]
[[Category:Biodegradable plastics]]
[[Category:Thermoplastics]]
[[Category:Bioplastics]]