Editing Arsenic (section)

=== Bacteria ===
Some species of bacteria obtain their energy in the absence of oxygen by [[redox|oxidizing]] various fuels while [[redox|reducing]] arsenate to arsenite. Under oxidative environmental conditions some bacteria use arsenite as fuel, which they oxidize to arsenate.<ref>{{cite journal|last1 = Stolz|first1 = John F.|last2 = Basu|first2 = Partha|last3 = Santini|first3 = Joanne M.|last4 = Oremland|first4 = Ronald S.|s2cid = 2575554|title = Arsenic and Selenium in Microbial Metabolism|journal = Annual Review of Microbiology|volume = 60|pages = 107–130|date = 2006|doi = 10.1146/annurev.micro.60.080805.142053|pmid=16704340| bibcode=2006ARvMb..60..107S }}</ref> The [[enzyme]]s involved are known as [[Arsenate reductase (glutaredoxin)|arsenate reductases]] (Arr).<ref>{{cite journal |doi = 10.1111/j.1574-6976.2002.tb00617.x |title = Microbial arsenic: From geocycles to genes and enzymes |date = 2002 |last1 = Mukhopadhyay |first1 = Rita |last2 = Rosen |first2 = Barry P. |last3 = Phung |first3 = Le T. |last4 = Silver |first4 = Simon |journal = FEMS Microbiology Reviews |volume = 26 |issue = 3 |pages = 311–325 |pmid = 12165430| doi-access = free }}</ref>

In 2008, bacteria were discovered that employ a version of [[photosynthesis]] in the absence of oxygen with arsenites as [[electron donor]]s, producing arsenates (just as ordinary photosynthesis uses water as electron donor, producing molecular oxygen). Researchers conjecture that, over the course of history, these photosynthesizing organisms produced the arsenates that allowed the arsenate-reducing bacteria to thrive. One [[strain (biology)|strain]], PHS-1, has been isolated and is related to the [[gammaproteobacterium]] ''[[Ectothiorhodospira shaposhnikovii]]''. The mechanism is unknown, but an encoded Arr enzyme may function in reverse to its known [[homology (biology)|homologues]].<ref>{{cite journal |last1=Kulp |first1=T.R |last2= Hoeft |first2= S.E. |last3= Asao |first3= M. |last4= Madigan |first4= M.T. |last5= Hollibaugh |first5= J.T. |last6= Fisher |first6= J.C. |last7= Stolz |first7= J.F. |last8= Culbertson |first8= C.W. |last9= Miller |first9= L.G.|first10=R.S. |last10=Oremland |display-authors=6 |year = 2008 |title = Arsenic(III) fuels anoxygenic photosynthesis in hot spring biofilms from Mono Lake, California|journal = [[Science (journal)|Science]]|volume = 321 |issue = 5891|pages = 967–970|doi = 10.1126/science.1160799 |pmid= 18703741 |s2cid = 39479754|bibcode = 2008Sci...321..967K}}
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{{cite magazine |first=Fred |last=Campbell |date=11 August 2008 |title=Arsenic-loving bacteria rewrite photosynthesis rules |magazine=Chemistry World |url=https://www.chemistryworld.com/news/arsenic-loving-bacteria-rewrite-photosynthesis-rules/3000398.article }}</ref>

In 2010, researchers reported the discovery of a strain of the bacterium ''[[Halomonas]]'' (designated GFAJ-1) that was allegedly capable of substituting arsenic for phosphorus in its biomolecules, including DNA, when grown in an arsenic-rich, phosphate-limited environment. This claim, published in ''Science'', suggested that arsenic could potentially serve as a building block of life in place of phosphorus, challenging long-standing assumptions about biochemical requirements for life on Earth.<ref>{{Cite journal |last1=Wolfe-Simon |first1=Felisa |last2=Blum |first2=Jodi Switzer |last3=Kulp |first3=Thomas R. |last4=Gordon |first4=Gwyneth W. |last5=Hoeft |first5=Shelley E. |last6=Pett-Ridge |first6=Jennifer |last7=Stolz |first7=John F. |last8=Webb |first8=Samuel M. |last9=Weber |first9=Peter K. |last10=Davies |first10=Paul C. W. |last11=Anbar |first11=Ariel D. |last12=Oremland |first12=Ronald S. |date=2011-06-03 |title=A Bacterium That Can Grow by Using Arsenic Instead of Phosphorus |url=https://www.science.org/doi/10.1126/science.1197258 |journal=Science |volume=332 |issue=6034 |pages=1163–1166 |doi=10.1126/science.1197258|pmid=21127214 |bibcode=2011Sci...332.1163W }}</ref>

The claim was met with widespread skepticism. Subsequent studies provided evidence contradicting the initial findings. One follow-up study published in ''Science'' in 2011 demonstrated that GFAJ-1 still requires phosphate to grow and does not incorporate arsenate into its DNA in any biologically significant way.<ref>{{Cite journal |last1=Cotner |first1=James B. |last2=Hall |first2=Edward K. |date=2011-06-03 |title=Comment on "A Bacterium That Can Grow by Using Arsenic Instead of Phosphorus" |url=https://www.science.org/doi/10.1126/science.1201943 |journal=Science |volume=332 |issue=6034 |pages=1149 |doi=10.1126/science.1201943|pmid=21622705 |bibcode=2011Sci...332R1149C }}</ref> Another independent investigation in 2012 used more sensitive techniques to purify and analyze the DNA of GFAJ-1 and found no detectable arsenate incorporated into the DNA backbone. The authors concluded that the original observations were likely due to experimental contamination or insufficient purification methods.<ref>{{Cite journal |last1=Erb |first1=Tobias J. |last2=Kiefer |first2=Patrick |last3=Hattendorf |first3=Bodo |last4=Günther |first4=Detlef |last5=Vorholt |first5=Julia A. |date=2012-07-27 |title=GFAJ-1 Is an Arsenate-Resistant, Phosphate-Dependent Organism |url=https://www.science.org/doi/10.1126/science.1218455 |journal=Science |volume=337 |issue=6093 |pages=467–470 |doi=10.1126/science.1218455|pmid=22773139 |bibcode=2012Sci...337..467E }}</ref> Together, these studies reaffirmed phosphorus as an essential element for all known forms of life.