Bacteria Genomes - SINORHIZOBIUM MELILOTI

Sinorhizobium meliloti, formerly Rhizobium meliloti, is a common Gram-negative soil and rhizosphere bacterium.

One of the most interesting and perhaps best-studied plant bacterial interactions is between rhizobial species and economically important leguminous plants (soybean, alfalfa, beans, peas, etc.). Rhizobia are generally described as root-nodule-forming nitrogen-fixing symbionts belonging to one of five species, Rhizobium, Bradyrhizobium, Sinorhizobium, Azorhizobium, and Mesorhizobium.

Sinorhizobium meliloti lives on the roots of alfalfa plants and other legumes. Analyses of the genome sequence revealed some of the mechanisms involved in the organism's symbiotic relationship with alfalfa and its ability to transform atmospheric nitrogen into a form that plants can use for growth. Bacteria such as S. meliloti not only provide nitrogen to their plant host, but also leave behind excess nitrogen in the soil, potentially reducing the need for fertilisers.

Sinorhizobium meliloti and alfalfa can grow in isolation from each other, but when brought together, they enter into a symbiotic relationship. The bacterium enters the root tissue via infection threads and forms growths (nodules) on the roots of the alfalfa plants. Inside the nodules, it converts atmospheric nitrogen into ammonia, a nitrogen-based compound plants can use to produce proteins. In return, the plants provide a carbon and energy source for the bacteria.

S. meliloti is one of the best known Rhizobium as the consequence of being studied by a large number of groups worldwide. It is a fast growing Rhizobium, whose genome size is moderate (6.6 Mb) and which is readily amenable to genetic studies.

References:

http://www.ebi.ac.uk/integr8/QuickSearch.do?action=doOrgSearch&organismName=Sinorhizobium+meliloti
Proc Natl Acad Sci U S A : 98(17):9877-82 (2001)
http://sequence.toulouse.inra.fr/meliloti.html