View source for Lar1

'''LAR1''' ('Lichen-Associated Rhizobiales 1') refers to a specific bacterial lineage in the order [[Hyphomicrobiales]] (formerly Rhizobiales) that has most frequently been found directly in association with [[lichen]]s.<ref name="duke">{{cite journal |doi=10.1007/s13199-009-0049-3 |vauthors=Hodkinson BP, Lutzoni F |title=A microbiotic survey of lichen-associated bacteria reveals a new lineage from the Rhizobiales |journal=Symbiosis |volume=49 |pages=163–180 |year=2009 |url=http://www.duke.edu/~bph8/Hodkinson_and_Lutzoni_2009.pdf |issue=3 |bibcode=2009Symbi..49..163H |s2cid=4129219 |access-date=2009-12-09 |archive-url=https://web.archive.org/web/20121017051702/http://www.duke.edu/~bph8/Hodkinson_and_Lutzoni_2009.pdf |archive-date=2012-10-17 |url-status=dead }}</ref>
This lineage is currently known to associate with lichens that have a [[green algae|green-algal]] [[photosynthesis|photosynthetic]] partner (as opposed to a [[cyanobacteria]]l partner) and a [[fungus|fungal]] partner in the [[Lecanoromycetes]] (though other groups of fungi have not yet been examined).  This lineage has been documented in association with all green-algal lichens specifically tested (all from North America), and was also found in a sequence library derived from Antarctic lichens.<ref>{{cite journal |doi=10.1128/AEM.69.7.3858-3867.2003 |author=De la Torre JR, Goebel BM, Friedmann EI, Pace, NR |title=Microbial Diversity of Cryptoendolithic Communities from the McMurdo Dry Valleys, Antarctica |journal=Applied and Environmental Microbiology |volume=69 |issue=7 |pages=3858–3867 |year=2003 |pmid=12839754 |pmc=165166|bibcode=2003ApEnM..69.3858D }}</ref>  The specific [[ecological niche]] occupied by this lineage indicates that it may rely on certain nutrients that are abundant in green-algal lichen [[thallus|thalli]] but are rarer in other environments.
==Nitrogen fixing==
The LAR1 lineage is currently defined based on sequences of the [[16S ribosomal RNA|16S rRNA gene]] alone, since it remains uncultured in the laboratory.  In spite of its resistance to being cultured, at least one potentially significant metabolic function can be inferred through circumstantial evidence: [[nitrogen fixation]].  Since [[nitrogen]] is required for growth by all biological systems, but is generally biologically inaccessible due to its high [[activation energy]], many eukaryotes have established relationships with specialized bacteria that are capable of nitrogen fixation (converting dinitrogen gas into a molecular form which is easily assimilated).<ref>{{cite journal |vauthors=Cabello P, Roldán MD, Moreno-Vivián C |title=Nitrate reduction and the nitrogen cycle in archaea |journal=Microbiology |volume=150 |issue=Pt 11 |pages=3527–46 |date=November 2004 |pmid=15528644 |doi=10.1099/mic.0.27303-0 |url=http://mic.sgmjournals.org/cgi/content/full/150/11/3527?view=long&pmid=15528644|doi-access=free }}</ref>
Many lichens grow in extremely nutrient-poor environments and may rely on nitrogen-fixing bacteria to provide them with enough molecular nitrogen to survive.<ref>{{cite journal |author=Brodo, IM |title=Substrate ecology |journal=In: The Lichens. Ahmadjihan V, Hale ME, Eds. Academic Press, New York and London |pages=401–441 |year=1973}}</ref>  It has been documented by numerous researchers that microbes associated with green-algal lichens have the potential to fix nitrogen in abundance.<ref>{{cite journal | last=Henckel | first=P. A. |author2=T. T. Plotnikova  | title=[Nitrogen-fixing bacteria in lichens] |journal=Izvestiya Akademii Nauk SSSR. Seriya Biologicheskaya |volume=6 |pages=807–813 |year=1973|language=ru}}</ref><ref>{{cite journal |author=Krasil’nikov NA |title=Is Azotobacter present in lichens? |journal=Mikrobiologiia |volume=18 |page=3 |year=1949}}</ref><ref>{{cite journal |author=Lambright, DD Kapustka, LA |title=The association of N2-fixing bacteria with Dermatocarpon miniatum and Lepraria sp |journal=Botanical Society of America: Miscellaneous Serial Publication |volume=160 |page=5 |year=1981}}</ref><ref>{{cite journal |doi=10.1111/j.1365-2672.2006.03010.x |vauthors=Liba CM, Ferrara FI, Manfio GP, Fantinatti-Garboggini F, Albuquerque RC, Pavan C, Ramos PL, Moreira CA, Barbosa HR |title=Nitrogen-fixing chemo-organotrophic bacteria isolated from cyanobacteria-deprived lichens and their ability to solubilize phosphate and to release amino acids and phytohormones |journal=Journal of Applied Microbiology |volume=101 |issue=5 |pages=1076–1086 |year=2006 |pmid=17040231|doi-access=free }}</ref>
However, nearly all of these studies have relied solely on culture-based methods, which may provide an inaccurate picture of what the most abundant or important nitrogen-fixers are.  Independent studies on lichens have used culture-free techniques to detect the presence of [[Nif gene|nifH]], the primary gene involved in nitrogen fixation, and have uncovered sequences that share the same phylogenetic affinities as the LAR1 lineage.<ref name="duke" /><ref>{{cite journal |doi=10.1038/ismej.2009.63 |vauthors=Grube M, Cardinale M, Vieira de Castro J, Müller H, Berg G |title=Species-specific structural and functional diversity of bacterial communities in lichen symbiosis |journal=[[The ISME Journal]] |volume=3 |pages=1105–1115 |year=2009 |issue=9 |pmid=19554038|doi-access=free |bibcode=2009ISMEJ...3.1105G }}</ref>
However, the diversity of bacteria found in environmental samples, the frequency with which [[horizontal gene transfer]] occurs in bacteria, and the lack of physiological studies make a definitive statement regarding the metabolic activity of this uncultured lineage impossible at this point.
==References==
{{reflist|2}}
[[Category:Hyphomicrobiales]]
[[Category:Symbiosis]]
[[Category:Lichenology]]