|WikiProject Microbiology||(Rated Start-class, Mid-importance)|
|WikiProject Soil||(Rated Start-class, Mid-importance)|
This section needs an NPOV copyedit to remove terminology such as 'policing' and 'cheating'
Feel free to add a note that some people object to these terms, if you can cite an example of such objection in a peer-reviewed journal. But they are widely used in the evolution-of-cooperation literature. A few of the examples from the first three months of 2010: Edwards,D.P.2010Can the failure to punish promote cheating in mutualism?; El Mouden,C.2010The enforcement of cooperation by policing; Jander,K.C.2010Host sanctions and pollinator cheating in the fig tree-fig wasp mutualism. These terms don't imply conscious decisions any more than "host recognition" (without cognition!) in the plant pathology literature does.
The legume – rhizobium symbiosis is a classic example of mutualism — rhizobia supply ammonia or amino acids to the plant and in return receive organic acids (principally as the dicarboxylic acids malate and succinate) as a carbon and energy source — but its evolutionary persistence is actually somewhat surprising. Because several unrelated strains infect each individual plant, any one strain could redirect resources from nitrogen fixation to its own reproduction without killing the host plant upon which they all depend. But this form of cheating should be equally tempting for all strains, a classic tragedy of the commons. There are two competing hypotheses for the mechanism that maintains legume-rhizobium symbiosis. The sanctions hypothesis suggests that plants police cheating rhizobia. Sanctions could take the form of reduced nodule growth, early nodule death, decreased carbon supply to nodules, or reduced oxygen supply to nodules that fix less nitrogen.  The partner choice hypothesis proposes that the plant uses pre-nodulation signals from the rhizobia to decide whether to allow nodulation and chooses only non-cheating rhizobia. There is evidence in favor of sanctions, which shows that plants reduce the oxygen supply to nodules that fix less nitrogen.  However, other studies have found no evidence of plant sanctions and instead support the partner choice hypothesis.
Removed a paragraph added at the end that duplicates the main text and includes incorrect information. For example, it says the rhizobia make nitrate (they make ammonia) and says the plants take "some" (they take almost all) and that the benefit to rhizobia is protection from worms. The big benefit is carbohydrate -- someone edited this to "dicarboxylic acids as a C an energy source", which is an improvement -- which lets them reproduce up a millionfold inside the nodule. Should Allorhizobium really be listed as a rhizobia genus?. It is well established that Allorhizobium lies within the Rhizobium clade. One such reference is:
YOUNG (J.M.), KUYKENDALL (L.D.), MARTÍNEZ -ROMERO (E.), KERR (A.) and SAWADA (H.): A revision of Rhizobium Frank 1889, with an emended description of the genus, and the inclusion of all species of Agrobacterium Conn 1942 and Allorhizobium undicola de Lajudie et al. 1998 as new combinations: Rhizobium radiobacter, R. rhizogenes, R. rubi, R. undicola and R. vitis. Int. J. Syst. Evol. Microbiol., 2001, 51, 89-103.
Additionally see the external link to rhizobia taxonomy. Also there is a valid change of the name Sinorhizobium to Ensifer, but this is still under contention by some taxonomists. I suggest we leave Sinorhizobium as is for now. Onco p53 00:37, 13 Oct 2004 (UTC)
I also think this should be moved to rhizobia rather than rhizobium bacteria this better reflects what this page is about, not just the rhizobium genus, I'll leave it until late november when I get back from a conference in china. Unless there are objections. Onco p53 05:02, 19 Oct 2004 (UTC)
OK done the move now, I also changed a bunch of redirect pages Onco p53 11:12, 26 Nov 2004 (UTC)
Regarding Enisfer, I'd recommend adding it at least in parentheses after "Sinorhizobium" as according to taxonomic rules this name takes precedence. Sinorhizobium is only still kept because Sinorhizobium-workers are fed up with yet another change in names. See: Int J Syst Evol Microbiol. 2003 Nov;53(Pt 6):2107-10.
- Could references (other than web pages) be inserted in this page?
- In particular, the claims about Agrobacterium and its relatedness to to Rhizobium and other rhizobia are confusing. I have heard that they are closely related before. Postgate (1998:Nitrogen fixation, Cambridge Univ.) says that attempts to insert the N-fixing genes from Klebsiella into Agrobacterium do not result in N-fixing ability, although other bacteria have been so transformed. I couldn't find further references to this issue.--Satyrium 21:25, 3 August 2006 (UTC)