Listeria welshimeri

Classification

Higher order taxa Domain; Phylum; Class; Order; Family; Genus Bacteria; Firmicutes; Bacilli; Bacillales; Listeriaceae; Listeria

Species Listeria welshimeri

Description and significance Listeria welshimeri, is one of six species that belongs to the genus Listeria. It is motile, gram-positive, facultative anaerobic rod-like bacteria that is ubiquitous in nature (2). L. welshimeri can be found in decaying plants, soil, sewage, dust and water. L. welshimeri was first isolated from decaying plants. These bacteria are small ( 0.5 to 2.0µm), non-spore-forming and are motile below 30degrees C by means of peritrichous flagella that uniformly cover its body (2).There are two pathogenic strains of Listeria, including L. monocytogenes and L. ivanovii and there are four non pathogenic strains which include L. L. innocua, L. seeligeri, L. grayi and L. welshimeri (3). L. welshimeri is an important organism because of it is similar to L. monocytogenes, which is a food-borne pathogen.L. welshimeri was analyzed to compare its genome sequence to that of L. monocytogenes in order to learn more about this pathogen.

Genome sequence Listeria welshimeri has a circular chromosome that is made of 2,814,130 base pairs, giving it the smallest genome size of the genus Listeria. It has a low G+C content (36.4%) giving its DNA a less rigid structure. The origin of replication and terminus are located about 1,400 kb apart. Its genome contains six complete copies of rRNA operons (16S-22S-5S) (4). L. welshimeri contains plasmids pBcloBAC11, pCC1FOS, pCR4Blunt-TOPO and pUC19 which are cloning vectors for E. coli. There are 233 gene deletions in L. welshimeri when compared to L. monocytogenes and the majority of the deleted portions are in gene clusters. These deletions originate at the same loci in the chromosome. Two surface-associated proteins, leucine-rich repeat (LRR) and LPXTG motifs have been lost in L. welshimeri. These proteins are required for adhering and invading nonphagocytic cells (4).