''Leuconostoc mesenteroides'' is a species of

lactic acid bacteria Lactobacillales are an order of gram-positive, low-GC, acid-tolerant, generally nonsporulating, nonrespiring, either rod-shaped (bacilli) or spherical ( cocci) bacteria that share common metabolic and physiological characteristics. These bact ...

associated with

fermentation Fermentation is a type of anaerobic metabolism which harnesses the redox potential of the reactants to make adenosine triphosphate (ATP) and organic end products. Organic molecules, such as glucose or other sugars, are catabolized and reduce ...

, under conditions of

salinity Salinity () is the saltiness or amount of salt (chemistry), salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensio ...

and low temperatures (such as

lactic acid Lactic acid is an organic acid. It has the molecular formula C3H6O3. It is white in the solid state and it is miscible with water. When in the dissolved state, it forms a colorless solution. Production includes both artificial synthesis as wel ...

production in fermented sausages). In some cases of vegetable and food storage, it was associated with pathogenicity (soft rot, slime and unpleasant odor). ''L. mesenteroides'' is approximately 0.5-0.7 μm in diameter and has a length of 0.7-1.2 μm, producing small grayish colonies that are typically less than 1.0 mm in diameter. It is facultatively

anaerobic Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to: *Adhesive#Anaerobic, Anaerobic ad ...

Gram-positive In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. The Gram stain is ...

, non-motile, non-sporogenous, and

spherical A sphere (from Ancient Greek, Greek , ) is a surface (mathematics), surface analogous to the circle, a curve. In solid geometry, a sphere is the Locus (mathematics), set of points that are all at the same distance from a given point in three ...

. It often forms lenticular coccoid cells in pairs and chains, however, it can occasionally form short rods with rounded ends in long chains, as its shape can differ depending on what media the species is grown on. ''L. mesenteroides'' grows best at 30 °C, but can survive in temperatures ranging from 10 °C to 30 °C. Its optimum pH is 5.5, but can still show growth in pH of 4.5-7.0.

Microbiological characteristics

''L. mesenteroides'' is an obligate heterolactic fermentative lactic acid bacterium ( LAB) that is mostly used in industrial dairy fermentation, playing various roles, such as production of

dextran Dextran is a complex branched glucan (polysaccharide derived from the condensation of glucose), originally derived from wine. IUPAC defines dextrans as "Branched poly-α-d-glucosides of microbial origin having glycosidic bonds predominantly C-1 ...

gas Gas is a state of matter that has neither a fixed volume nor a fixed shape and is a compressible fluid. A ''pure gas'' is made up of individual atoms (e.g. a noble gas like neon) or molecules of either a single type of atom ( elements such as ...

, and flavor compounds. It is approximately 0.5-0.7 μm by 0.7-1.2 μm, and produces small grayish colonies that are usually less than 1.0 mm in diameter. ''L. mesenteroides'' is a facultative

anaerobe An anaerobic organism or anaerobe is any organism that does not require molecular oxygen for growth. It may react negatively or even die if free oxygen is present. In contrast, an aerobic organism (aerobe) is an organism that requires an oxygenat ...

and will undergo heterolactic fermentation under

microaerophilic A microaerophile is a microorganism that requires environments containing lower levels of dioxygen than that are present in the atmosphere (i.e. < 21% O₂; typically 2–10% O₂) for optimal growth. A more r ...

conditions. Taking this into consideration, it is important to note that ''L. mesenteroides'' utilizes sugar glucose as its primary source of

metabolism Metabolism (, from ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes; the co ...

, also well as other sugars such as

sucrose Sucrose, a disaccharide, is a sugar composed of glucose and fructose subunits. It is produced naturally in plants and is the main constituent of white sugar. It has the molecular formula . For human consumption, sucrose is extracted and refined ...

and

fructose Fructose (), or fruit sugar, is a Ketose, ketonic monosaccharide, simple sugar found in many plants, where it is often bonded to glucose to form the disaccharide sucrose. It is one of the three dietary monosaccharides, along with glucose and gal ...

. Then, it creates

ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...

, lactate, and CO₂ as products of

. When grown in

solution, it converts the

sugar Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecul ...

s having mostly alpha 1,6 linkages, but 1,2, 1,3, and 1,4 linkages are also present.

Environment

''L. mesenteroides'' is typically found on the skin of a large variety of fleshy fruits and vegetables, and can be cultured using

MRS agar De Man–Rogosa–Sharpe agar, often abbreviated to MRS, is a Selective medium, selective Microbiological culture, culture medium designed to favour the luxuriant growth of ''Lactobacilli'' for lab study. Developed in 1960, this medium was named ...

, tomato juice agar, MRS broth, and

skim milk Skimmed milk (British English), or skim milk (American English), is made when all the milkfat is removed from whole milk. It tends to contain around 0.1% to 0.3% fat. Background Historically, skimmed milk was used for fattening pigs, and was re ...

. These common media are not ideal for growth and specialized media are needed to grow to a high cell density. This microbe is commonly used for souring vegetables like cucumbers and cabbage, producing fermented foods such as

kimchi Kimchi (; ) is a traditional Korean side dish (''banchan'') consisting of salted and fermented vegetables, most often napa cabbage or Korean radish. A wide selection of seasonings are used, including '' gochugaru'' (Korean chili powder), ...

sauerkraut Sauerkraut (; , ) is finely cut raw cabbage that has been fermented by various lactic acid bacteria. It has a long shelf life and a distinctive sour flavor, both of which result from the lactic acid formed when the bacteria ferment the sugar ...

, and

pickles Pickle, pickled or Pickles may refer to: Food * Pickle, a food that has undergone pickling * Pickled cucumber * Pickle, a sweet, vinegary pickled chutney popular in Britain, such as Branston Pickle, also known as "sweet pickle" or "ploughman's ...

. The bacteria is included in dairy starter cultures since they are able to produce metabolites needed for dairy production. These metabolites include diacetyl and CO₂ from citric acid. Diacetyl is important for dairy because it is the main source of aroma and flavor in many different dairy products, like

buttermilk Buttermilk is a fermented dairy drink. Traditionally, it was the liquid left behind after churning butter out of cultured cream. As most modern butter in Western countries is not made with cultured cream but uncultured sweet cream, most mode ...

, butter, and different cheeses. The production of CO₂ is important for the eye formation in many cheeses such as Havarti. Specialized media are commonly used for industrial growth because components in standard media like MRS contain meat extract and peptone that is not

Kosher (also or , ) is a set of dietary laws dealing with the foods that Jewish people are permitted to eat and how those foods must be prepared according to Jewish law. Food that may be consumed is deemed kosher ( in English, ), from the Ashke ...

halal ''Halal'' (; ) is an Arabic word that translates to in English. Although the term ''halal'' is often associated with Islamic dietary laws, particularly meat that is slaughtered according to Islamic guidelines, it also governs ethical practices ...

which is needed for many dairy and vegetable products. ''L. mesenteroides'' does best in temperatures ranging between 10 °C to 30 °C, but has an optimum temperature of 30 °C. Additionally, it can survive in a pH range of 4.5-7.0, with an optimum of 5.5-6.5. ''L. mesenteroides'' also has a doubling time of 0.6 h⁻¹ under aerobic conditions.

Genetics

The genome of ''L. mesenteroides'' has been successfully mapped, having an average

genome size Genome size is the total amount of DNA contained within one copy of a single complete genome. It is typically measured in terms of mass in picograms (trillionths or 10−12 of a gram, abbreviated pg) or less frequently in daltons, or as the tot ...

of 1.90138 Mbp and 1762 protein genes, with a G+C content of 37.8%. ''L. mesenteroides'' is from the phylum

Bacillota The Bacillota (synonym Firmicutes) are a phylum of bacteria, most of which have Gram-positive cell wall structure. They have round cells, called cocci (singular coccus), or rod-like forms (bacillus). A few Bacillota, such as '' Megasphaera'', ...

, and is a member of the lactic bacteria family. This is important as it has the ability to produce

which lowers the pH of the surrounding environment and, in turn, inhibits other competing food spoilage organism's growth as they cannot tolerate the acidic environment.

Health risks

''Leuconostoc mesenteroides'' subsp. ''mesenteroides'' has been found to show pathogenic characteristics in rare cases. The first case of this infecting a human was in 1985. A more recent outbreak in a hospital in 2004 had 48 cases where it was found that penicillin and gentamicin could be used as antimicrobial treatment. Samples of the bacteria were isolated in both the patient's blood and urine.

Taxonomy

''L. mesenteroides'' is divided into several subspecies. : ''L. m.'' subsp. ''cremoris'' (Knudsen and Sørensen 1929) Garvie 1983 : ''L. m.'' subsp. ''dextranicum'' (Beijerinck 1912) Garvie 1983 : ''L. m.'' subsp. ''mesenteroides'' (Tsenkovskii 1878) Garvie 1983 : ''L. m.'' subsp. ''suionicum'' Gu et al. 2012

Subspecies characteristics

Subsp. Mesenteroides

This strain can grow in NaCl up to 3.0% and some strains up to 6.5% and optimum temperature of 20 and 30 °C. It has also been found that when growth occurs in milk with supplemental yeast extract and glucose, enough acid is produced to curdle milk. Some, but not all strains can ferment citrate. Different strains of Subsp. Mesenteroides tested also differ by their need for riboflavin, pyridoxal and folic acid, these need to be tested to determine a starting point for the media. Tween 80, uracil and combinations of uracil, adenine, and xanthine are not required for growth. Subsp. Mesenteroides also require glutamic acid and valine.

Subsp. Cremoris

This strain grows best between 18 and 25 °C.This strain can ferment citrate into acetoin and diacetyl. Most strains of this subspecies cannot ferment sucrose. Of the three subspecies, this ferments the least kinds of carbohydrates. All strains can ferment glucose and lactose; galactose and maltose is strain specific. This strain requires more nutrients, riboflavin, pyridoxal, folic acid, uracil and a combination of uracil, adenine, and xanthine are required.

Subsp. Dextranicum

This strain is similar to Subsp. Mesenteroides, the optimum temperature of 20 and 30 °C. It can also ferment Glucose, fructose, lactose, maltose, sucrose and trehalose. There is also a variation by strain for requirements of riboflavin, pyridoxal and folic acid. Some strains also required a combination of uracil, guanine, adenine and xanthine.

References

External links

Type strain of ''Leuconostoc mesenteroides'' at Bac''Dive'' - the Bacterial Diversity Metadatabase
{{Taxonbar, from=Q146954 Lactobacillaceae Bacteria described in 1878