Abstract
Mesorhizobium opportunistum strain WSM2075T was isolated in Western Australia in 2000 from root nodules of the pasture legume Biserrula pelecinus that had been inoculated with M. ciceri bv. biserrulae WSM1271. WSM2075T is an aerobic, motile, Gram negative, non-spore-forming rod that has gained the ability to nodulate B. pelecinus but is completely ineffective in N2 fixation with this host. This report reveals that the genome of M. opportunistum strain WSM2075T contains a chromosome of size 6,884,444 bp, encoding 6,685 protein-coding genes and 62 RNA-only encoding genes. The genome contains no plasmids, but does harbor a 455.7 kb genomic island from Mesorhizobium ciceri bv. biserrulae WSM1271 that has been integrated into a phenylalanine-tRNA gene.
Highlights
Biserrula pelecinus L. is an autogamous annual legume species that is common, though never dominant, on coarse textured and acidic Mediterranean soils [1] and can often be found with other annual legumes including subterranean clover (Trifolium subterraneum) and serradella (Ornithopus) [2]
At the time of introduction, the Australian resident rhizobial populations were not capable of nodulating B. pelecinus [1,3] and a Mediterranean strain Mesorhizobium ciceri bv. biserrulae WSM1271 had to be used as an inoculant to establish an effective nitrogen fixing symbiosis
After 6 years of cultivation of B. pelecinus under field conditions, an isolate was recovered from root nodules of plants grown near Northam, Western Australia that displayed an ineffective symbiotic phenotype [4]
Summary
Biserrula pelecinus L. is an autogamous annual legume species that is common, though never dominant, on coarse textured and acidic Mediterranean soils [1] and can often be found with other annual legumes including subterranean clover (Trifolium subterraneum) and serradella (Ornithopus) [2]. This reseeding legume was introduced to Western Australia in 1993 in a pasture legume breeding and selection program that sought to develop new pasture legume options for the sandy surfaced duplex, acidic soils in Western Australia, to improve soil fertility and farming system flexibility [1]. Accumulated evidence revealed that WSM2075 had gained the ability to nodulate (but not fix with) B. pelecinus by acquiring symbiotic genes from the original inoculant strain Mesorhizobium ciceri bv. We reveal that a 455.7 kb genomic island from the inoculant Mesorhizobium ciceri bv. biserrulae WSM1271 has been horizontally transferred into M. opportunistum strain WSM2075T and integrated into the phenylalanine-tRNA gene
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