Leuconostoc mesenteroides

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Leuconostoc mesenteroides, under SEM.

Classification

Higher Order Taxonomic Information

Bacteria; Firmicutes; Bacilli; Lactobacillales; Leuconostocaceae

Species Name

Leuconostoc mesenteroides subsp. mesenteroides ATCC 8293

NCBI: Taxonomy

Species Description

The species is generally viewed as being a cocci, forming long chains or pairs during its growth. However, the morphology can change depending on what media the species is grown on, which can change them to rod shaped or more simply, elongated forms. The cells are Gram positive, which can aid in identification in human pathology. The bacteria is also a sporogenous and non-motile species. They are a facultative anaerobe and are a member of the lactic acid bacteria family, which includes O. oeni, which are also closely related to the Lactobacillaceae (also a LAB), which split off from the Streptococcaceae (Marakova et al. 2006).

Applications and Uses

L. mesenteroides is primarily found upon the skins of a large variety fruits and vegetables. Under the correct micro anaerobic conditions, the L. mesenteries is actually responsible for beginning the fermentative processes on many standard foods such as kim-chi, sauerkraut, and it even is included in the starter cultures of various breads and dairy cultures (Server-Busson et al. 1999). On sauerkraut specifically, the pH is lowered in the first phase by Klebsiella and Enterobacter species. This lowers the pH so that L. mesenteries can take hold and further lower the pH. The third and final stage of the fermentation is then taken up by other LABs related to L. mesteroides (namely, L. pantarum), and lowers the pH even more. (Belitz et al. 2009). With L. mesteroides, this process would be missing a niche in which the full fermentation of a commercial product could not be completed, and shows the importance that L. mesteroides has in shaping its own environment. This feature is also utilized in the meat and dairy industry, as L. mesenteroides produces a chemical known as bacterioicin, which prevents the growth of other bacterial species, further increasing its evidence as a shaper of its environment.

Genome

Leuconostoc mesenteroides genome structure

L. mesenteroides has a circular chromosome with 2075763 nucleotides, 2003 protein encoding genes, and 85 RNA genes, around 54% of which have a known purpose. The genome is circular and does contain a variety of plasmids, which aid in citrate metabolism, and bacterioicin development. L. mesenteroides also reproduces by binary fission by first copying its circular genome, and then splitting, and each respective daughter cell gets a copy of the circular genome and plasmids. KEGG Genome

The lactic acid bacteria genomes generally encode for carbon and nitrogen acquisition within their environments. These genes seem to have spawned from the process of horizontal gene transfer as a coevolutionary method from their habitats (Marakova et al. 2006). The L. mesenteroides genome also has relatively few pseudogenes, which number less than 20 on average (Bolotin et al. 2004).

Metabolism

Schematic representation of carbon and energy flow through the central metabolic pathways of L. mesenteroides during metabolism of various sugars. G1P, glucose-1-phosphate; G6P, glucose-6-phosphate; F6P, fructose-6-phosphate; GAP, glyceraldehyde-3-phosphate; acetyl-P, acetylphosphate; acetyl-CoA, acetyl coenzyme A; 1, sucrose phosphorylase; 2, dextransucrase; 3,phosphoglucomutase (PGM); 4, glucokinase; 5, fructokinase; 6, mannitol dehydrogenase; 7, pyruvate dehydrogenase.

L. mesenteroides is a facultative anaerobe, and under microaerophilic conditions, will undergo a heterolactic fermentation. This results in the break down of glucose and other sugars into D-lactate, ethanol, and CO2 (Demoss et al 1951; Garvie 1986; Gottschalk 1986). It will also convert citrate into diacetyl and acetoin, and will convert sucrose into destrans and levan. Dextrans are used for a variety of different commercial products, some of which include cosmetics, blood plasma extenders, and heparin substitutes (Leathers et al 1995; Sutherland 1996; Alsop 1983; Kim and Day 1994). A variety of polysaccharides are also produced from the metabolic pathways which creates a gel that renders the product unusable, and therefore necessary precautions have to be taken to avoid an accumulation of unwanted metabolite (Tallgren et al. 2006). There are many pathways L. mesenteroides uses in its metabolism which has beginning products of sucrose, fructose, and glucose. Some end products of note are mannitol, acetate, and lactate, but other pathways exist.

Pathogenesis and Human Infection

L. mesenteroidies is a normal occurrence on fruits and vegetables, and is generally not considered to be an infectious agent in humans. However, there are certain documented instances where L. mesenteroidies has actually caused disease within humans. The most surprising of which was a case study where a woman, who was originally thought to have brain tumors, actually had two purulent lesions in her brain that were later successfully identified as an L. mesenteroidies infection (Albanese et al. 2006). Another case is shown where Leuconostoc species are found in cancer patients, and within patients who are critically ill, immunocompromised, or nonsocomial (Cuervo et al. 2008). L. mesenteroides is an opportunistic pathogen, and is not wide-spread in disease, but in more recent years, a large variety of diagnoses have found infections among human patients, meaning it has the potential to infect human hosts. At this time, L. mesenteroides is not generally considered a threat unless in immunosuppressed hosts, and studies are ongoing.