Ensifer meliloti бактериясының сипаттамасы

Species of bacterium

Ensifer meliloti (formerly Rhizobium meliloti and Sinorhizobium meliloti) are an aerobic, Gram negative, and diazotrophic species of bacteria. S. meliloti are motile and possess a cluster of peritrichous flagella. These techniques reduce the need for inorganic nitrogenous fertilizers.

Symbiosis between S. meliloti and its legume hosts begins when the plant secretes an array of betaines and flavonoids into the rhizosphere: 4,4′ dihydroxy 2′ methoxychalcone, cynaroside, liquiritigenin, luteolin, 3′,5 dimethoxyluteolin, and trigonelline. Leghemoglobin, produced by leguminous plants after colonization of S. meliloti, interacts with the free oxygen in the root nodule where the rhizobia reside. Rhizobia are contained within symbiosomes in the root nodules of leguminous plants. The leghemoglobin reduces the amount of free oxygen present. Oxygen disrupts the function of the nitrogenase enzyme in the rhizobia, which is responsible for nitrogen fixation.

The S. meliloti genome contains four genes coding for flagellin. These include fliC1C2–fliC3C4. The genome contains three replicons: a chromosome (~3.7 megabases), a chromid (pSymB; ~1.7 megabases), and a plasmid (pSymA; ~1.4 megabases). Individual strains may possess additional, accessory plasmids. Five S. meliloti genomes have been sequenced to date: Rm1021, AK83, BL225C, and SM11 with 1021 considered to be the wild type. Indeterminate nodule symbiosis by S. meliloti is conferred by genes residing on pSymA.

The proteins encoded by E. meliloti genes uvrA, uvrB and uvrC are employed in the repair of DNA damages by the process of nucleotide excision repair. E. meliloti is a desiccation tolerant bacterium. However, E. meliloti mutants defective in either genes uvrA, uvrB or uvrC are sensitive to desiccation, as well as to UV light. This finding indicates that the desiccation tolerance of wild type E. meliloti depends on the repair of DNA damages that can be caused by desiccation.