Editing Polyhydroxybutyrate (section)

==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]]