Editing Escherichia coli (section)

=== Metabolism ===
''E. coli'' can live on a wide variety of substrates and uses [[mixed acid fermentation]] in anaerobic conditions, producing [[lactic acid|lactate]], [[succinate]], [[ethanol]], [[acetate]], and [[carbon dioxide]]. Since many pathways in [[Mixed acid fermentation|mixed-acid fermentation]] produce [[hydrogen]] gas, these pathways require the levels of hydrogen to be low, as is the case when ''E. coli'' lives together with hydrogen-consuming organisms, such as [[methanogen]]s or [[sulphate-reducing bacteria]].<ref>{{cite book | title=Brock Biology of microorganisms|vauthors=Madigan MT, Martinko JM | year=2006| publisher=Pearson| isbn=978-0-13-196893-6| edition=11th}}</ref>

In addition, ''E. coli''{{'}}s metabolism can be rewired to solely use [[Carbon dioxide|CO<sub>2</sub>]] as the source of [[carbon]] for biomass production. In other words, this obligate heterotroph's metabolism can be altered to display autotrophic capabilities by heterologously expressing [[carbon fixation]] genes as well as [[formate dehydrogenase]] and conducting laboratory evolution experiments. This may be done by using [[formate]] to reduce [[electron carrier]]s and supply the [[Adenosine triphosphate|ATP]] required in anabolic pathways inside of these synthetic autotrophs.<ref>{{cite journal | vauthors = Gleizer S, Ben-Nissan R, Bar-On YM, Antonovsky N, Noor E, Zohar Y, Jona G, Krieger E, Shamshoum M, Bar-Even A, Milo R | display-authors = 6 | title = 2 | journal = Cell | volume = 179 | issue = 6 | pages = 1255–1263.e12 | date = November 2019 | pmid = 31778652 | pmc = 6904909 | doi = 10.1016/j.cell.2019.11.009 }}</ref>[[File:Ecoli_Metabolism.webp|thumb|''Redistribution of fluxes between the three primary glucose catabolic pathways: EMPP (red), EDP (blue), and OPPP (orange) via the knockout of pfkA and overexpression of EDP genes (edd and eda).'']]

''E. coli'' has three native glycolytic pathways: [[Embden–Meyerhof–Parnas pathway|EMPP]], [[Entner–Doudoroff pathway|EDP]], and [[Pentose phosphate pathway|OPPP]]. The EMPP employs ten enzymatic steps to yield two [[pyruvates]], two [[Adenosine triphosphate|ATP]], and two [[NADH]] per [[glucose]] molecule  while OPPP serves as an oxidation route for [[NADPH]] synthesis. Although the EDP is the more thermodynamically favourable of the three pathways, ''E. coli'' do not use the EDP for [[glucose metabolism]], relying mainly on the EMPP and the OPPP. The EDP mainly remains inactive except for during growth with [[gluconate]].<ref>{{cite journal | vauthors = Hollinshead WD, Rodriguez S, Martin HG, Wang G, Baidoo EE, Sale KL, Keasling JD, Mukhopadhyay A, Tang YJ | display-authors = 6 | title = pfk mutants | journal = Biotechnology for Biofuels | volume = 9 | issue = 1 | pages = 212 | date = 2016-10-10 | pmid = 27766116 | pmc = 5057261 | doi = 10.1186/s13068-016-0630-y | doi-access = free }}</ref>

==== Catabolite repression ====
When growing in the presence of a mixture of sugars, bacteria will often consume the sugars sequentially through a process known as [[Catabolism|catabolite]] repression. By repressing the expression of the genes involved in metabolizing the less preferred sugars, cells will usually first consume the sugar yielding the highest growth rate, followed by the sugar yielding the next highest growth rate, and so on. In doing so the cells ensure that their limited metabolic resources are being used to maximize the rate of growth. The well-used example of this with ''E. coli'' involves the growth of the bacterium on [[glucose]] and [[lactose]], where ''E. coli'' will consume [[glucose]] before [[lactose]]. Catabolite repression has also been observed in ''E. coli'' in the presence of other non-glucose sugars, such as [[arabinose]] and [[xylose]], [[sorbitol]], [[rhamnose]], and [[ribose]]. In ''E. coli'', glucose catabolite repression is regulated by the [[phosphotransferase system]], a multi-protein [[phosphorylation]] cascade that couples [[glucose uptake]] and [[metabolism]].<ref>{{cite journal | vauthors = Ammar EM, Wang X, Rao CV | title = Regulation of metabolism in ''Escherichia coli'' during growth on mixtures of the non-glucose sugars: arabinose, lactose, and xylose | journal = Scientific Reports | volume = 8 | issue = 1 | pages = 609 | date = January 2018 | pmid = 29330542 | pmc = 5766520 | doi = 10.1038/s41598-017-18704-0 | bibcode = 2018NatSR...8..609A }}</ref>