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Pelagibacterales

The Pelagibacterales is an order in the Alphaproteobacteria composed of free-living bacteria that make up roughly one in three cells at the ocean's surface.{{Cite journal | pmid = 24349502 | pmc = 3859672 | year = 2013 | author1 = Ferla | first1 = M. P. | title = New rRNA gene-based phylogenies of the Alphaproteobacteria provide perspective on major groups, mitochondrial ancestry and phylogenetic instability | journal = PLOS ONE | volume = 8 | issue = 12 | pages = e83383 | last2 = Thrash | first2 = J. C. | last3 = Giovannoni | first3 = S. J. | last4 = Patrick | first4 = W. M. | doi = 10.1371/journal.pone.0083383 }} Overall, members of the Pelagibacterales are estimated to make up between a quarter and a half of all prokaryotic cells in the ocean. Initially, this taxon was known solely by metagenomic data and was known as the SAR11 clade. It was first placed in the Rickettsiales, but was later raised to the rank of order, and then placed as sister order to the Rickettsiales in the subclass Rickettsidae. It includes the highly abundant marine species Pelagibacter ubique. Bacteria in this clade are unusually small. Pelagibacter ubique and related species are oligotrophs (scavengers) and feed on dissolved organic carbon and nitrogen. They are unable to fix carbon or nitrogen, but can perform the TCA cycle with glyoxylate bypass and are able to synthesise all amino-acids except glycine, and some cofactors. They also have an unusual and unexpected requirement for reduced sulfur. Pelagibacter ubique and members of the oceanic subgroup I possess gluconeogenesis but not a typical glycolysis pathway, whereas other subgroups are capable of typical glycolysis.{{Cite journal | last1 = Schwalbach | first1 = M. S. | last2 = Tripp | first2 = H. J. | last3 = Steindler | first3 = L. | last4 = Smith | first4 = D. P. | last5 = Giovannoni | first5 = S. J. | doi = 10.1111/j.1462-2920.2009.02092.x | title = The presence of the glycolysis operon in SAR11 genomes is positively correlated with ocean productivity | journal = Environmental Microbiology | volume = 12 | issue = 2 | pages = 490–500 | year = 2010 | pmid = 19889000 }} Unlike Acaryochloris marina it is not photosynthetic – specifically, it does not use light to increase the bond energy of an electron pair – but it does possess proteorhodopsin (incl. retinol biosynthesis) for ATP production from light. SAR11 bacteria are responsible for much of the dissolved methane in the ocean surface. They extract phosphate from methylphosphonic acid. The taxon derives its name from the type species Pelagibacter ubique. However, this species has not yet been validly published, and therefore neither the family name or the species name has official taxonomic standing.

Subgroups

Currently the (unofficial) family is divided into five subgroups:Robert M. Morris, K.L.V., Jang-Cheon Cho, Michael S. Rappé, Craig A. Carlson, Stephen J. Giovannoni, Temporal and Spatial Response of Bacterioplankton Lineages to Annual Convective Overturn at the Bermuda Atlantic Time-Series Study Site" Limnology and Oceanography 50(5) p. 1687-1696.
  • Subgroup Ia, open ocean, crown group — includes Pelagibacter ubique HTCC1062
  • Subgroup Ib, open ocean, sister clade to Ia
  • Subgroup II, coastal, basal to Ia + Ib
  • Subgroup III, brackish, basal to I + II along with its sister clade IV
  • Subgroup IV, also known as LD12 clade, freshwaterSalcher, M.M., J. Pernthaler, and T. Posch, Seasonal bloom dynamics and ecophysiology of the freshwater sister clade of SAR11 bacteria 'that rule the waves' (LD12). ISME J, 2011.
  • Subgroup V, which includes alphaproteobacterium HIMB59, basal to the remainder

Phylogenetic placement and Endosymbiotic theory

A 2011 study by researchers of the University of Hawaiʻi at Mānoa and the Oregon State University, indicate that SAR11 could be the ancestor of mitochondria in most eukaryotic cells. However, the result can be tree reconstruction artifacts due to compositional bias.

References

"green air" © 2007 - Ingo Malchow, Webdesign Neustrelitz
This article based upon the http://en.wikipedia.org/wiki/Pelagibacterales, the free encyclopaedia Wikipedia and is licensed under the GNU Free Documentation License.
Further informations available on the list of authors and history: http://en.wikipedia.org/w/index.php?title=Pelagibacterales&action=history
presented by: Ingo Malchow, Mirower Bogen 22, 17235 Neustrelitz, Germany