Abstract
Ensifer (Sinorhizobium) medicae is an effective nitrogen fixing microsymbiont of a diverse range of annual Medicago (medic) species. Strain WSM419 is an aerobic, motile, non-spore forming, Gram-negative rod isolated from a M. murex root nodule collected in Sardinia, Italy in 1981. WSM419 was manufactured commercially in Australia as an inoculant for annual medics during 1985 to 1993 due to its nitrogen fixation, saprophytic competence and acid tolerance properties. Here we describe the basic features of this organism, together with the complete genome sequence, and annotation. This is the first report of a complete genome sequence for a microsymbiont of the group of annual medic species adapted to acid soils. We reveal that its genome size is 6,817,576 bp encoding 6,518 protein-coding genes and 81 RNA only encoding genes. The genome contains a chromosome of size 3,781,904 bp and 3 plasmids of size 1,570,951 bp, 1,245,408 bp and 219,313 bp. The smallest plasmid is a feature unique to this medic microsymbiont.
Highlights
Agricultural systems are nearly always nitrogen deficient, a factor which grossly limits their productivity
Nitrogen can be obtained from symbiotic nitrogen fixation (SNF) by root nodule bacteria on nodulated legumes [4]
A particular suite of strains isolated from acidic soils on the Italian island of Sardinia proved to be acid soil tolerant [9], an attribute we know is related to the presence of a unique set of genes required for acid adaptation [10]. Characterization of these acid-tolerant isolates revealed that they belonged to the species E. medicae and could be symbiotically distinguished from the related species E. meliloti by their unique capacity to fix nitrogen in association with annual acid soil adapted Medicago hosts of worldwide agronomic value [11], as well as with the perennial forage legume M. sativa [12]
Summary
Agricultural systems are nearly always nitrogen deficient, a factor which grossly limits their productivity. Characterization of these acid-tolerant isolates revealed that they belonged to the species E. medicae and could be symbiotically distinguished from the related species E. meliloti by their unique capacity to fix nitrogen in association with annual acid soil adapted Medicago hosts of worldwide agronomic value [11], as well as with the perennial forage legume M. sativa (alfalfa) [12].
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