What Is Milk Kefir (Part 2 - STREPTOCOCCI / LACTOCOCCI)

Now it's time to take a look at some other organism found in milk kefir.  The Streptococci organisms are known as gram-positive facultative anaerobes.  They are also considered to be catalase-negative, as opposed to staphylococci, which are catalase-positive.  These gram-positive organisms are often found in pairs or chains and may be divided into different groups based on the ability of their antibodies to recognize a variety of different surface antigens.

Lactococcus is a genus that was formerly included in the Streptococcus Group N1.  These lactic acid bacteria are well known for their ability to produce lactic acid as their largest or only byproduct during glucose fermentation.  This group is gram-positive and catalase-negative as well, and can be found in pairs or chains as well as by themselves.  They are perhaps most famous at present for their use in cheese making.
http://pathmicro.med.sc.edu/fox/streptococci.htm  
http://en.wikipedia.org/wiki/Lactococcus

The following list can be found from it's original source located at Dom's Kefir HERE.

STREPTOCOCCI / LACTOCOCCI

Streptococcus thermophilus
S. paracitrovorus
Lactococcus lactis subsp. lactis
Lc. lactis subsp. lactis biovar. diacetylactis
Lc. lactis subsp. cremoris
Enterococcus durans
Leuconostoc mesenteroides subsp. cremoris
Leuc. mesenteroides subsp. mesenteroides
Leuc. dextranicum


Streptococcus thermophilus is an essential lactic acid bacterium used for commercial purposes, which includes the production of milk, cheese, and other dairy products. This organism is a thermophilic Gram-positive bacterium with an optimal growth rate at 45 °C. It is also capable of generating energy, in the form of adenosine triphosphate (ATP), by aerobic respiration with the presence of oxygen; however, without the presence of oxygen, it still can produce ATP through fermentation. S. thermophilus lacks cytochrome, oxidase, and catalase enzymes. It does not have motility and it does not form spores. Although S. thermophilus is closely related to other pathogenic streptococci (such as S. pneumoniae and S. pyogenes), S. thermophilus is classified as a non-pathogenic, alpha-hemolytic species that is part of the viridians group. The increasing consumer need for dairy products and booming manufacture of dairy products ($40 billion industry) led to the investigation and sequencing of S. thermophilus.
http://www.magma.ca/~pavel/science/Foods&bact.htm
http://microbewiki.kenyon.edu/index.php/Streptococcus_thermophilus

S.paracitrovorus does not readily dissimilate citric acid in the absence of sugar but does attack citric acid relatively vigorously in the presence of small quantities of glucose or lactose. The effect of glucose and lactose in initiating the dissimilation of citric acid is catalytic.
The sugars which act catalytically are themselves fermented to approximately equimolar quantities of carbon dioxide, ethyl alcohol and lactic acid. The dissimilation of a combined substrate of citrate and glucose forms, in addition, acetic acid, acetylmethylcarbinol, 2,3-butylene glycol and under certain conditions, pyruvic acid which acts as an intermediate compound. Pyruvate is dissimilated to products similar to those from a fermentation of citrate plus glucose.
The reactions ofKrebs' citric acid cycle apparently do not apply to the dissimilation of citric acid byS.paracitrovorus because the fermentation of citric acid proceeds anaerobically, consumes little oxygen aerobically and is not inhibited by arsenite.
Inasmuch as milk contains lactose, the fermentation of citric acid in milk byS.paracitrovorus may be catalyzed as shown in these studies.
Journal paper No.J711 of the Iowa Agricultural Experiment Station, Project 451.
http://www.springerlink.com/content/r1x11421311270r1/

The experiments have shown that although butter of exceptionally fine flavour can be produced by the use of pure culture starters of S. paracitrovorus under laboratory control, the uncertainties under practical conditions, due to its weak growth, are too marked to warrant its general use. Both S. citrovorus and S. paracitrovorus are unable to compete successfully with the inevitable contaminants encountered in practice. The value of vegetable media such as grass, silage and bean agar for growing streptococci such as S. paracitrovorus has been confirmed, but as observed by Orla-Jensen et al. (4) the subsequent growth in milk media lacks the vigour which might be expected.
http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=5124004

Lactococcus lactis subsp. lactis  is a Gram-positive bacterium used extensively in the production of buttermilk and cheese[1], but has recently also become famous as the first genetically modified organism to be used alive for the treatment of human disease [2]. L. lactis cells are cocci that group in pairs and short chains, and depending on growth conditions, appear ovoid with typically 0.5 - 1.5 µm in length. L. lactis does not produce spores (nonsporulating) and are not motile (nonmotile). They have a homofermentative metabolism and have been reported to produce exclusively L(+) lactic acid.[3] However,[4] reported D(-) lactic acid can be produced when cultured at low pH. The capability to produce lactic acid is one of the reasons L. lactis is one of the most important microorganisms in the dairy industry[5]. Generally, it has been considered as an opportunistic pathogen,[6] though the number of clinical cases associated with infections by these microorganisms has increased in the last decade in both humans and animals.[7][8] L. lactis is of crucial importance for manufacturing dairy products, such as buttermilk and cheeses. When L. lactis ssp. lactis is added to milk, the bacterium uses enzymes to produce energy molecules (ATP), from lactose. The byproduct of ATP energy production is lactic acid. The lactic acid produced by the bacterium curdles the milk that then separates to form curds, which are used to produce cheese.[9].

Other uses that have been reported for this bacterium include the production of pickled vegetables, beer or wine, some breads and other fermented foodstuffs, such as soymilk kefir, buttermilk, an others.[10]
http://jpkc.njau.edu.cn/spwswx/cankao/ShowArticle.asp?ArticleID=314
http://en.wikipedia.org/wiki/Lactococcus_lactis

Lc. lactis subsp. lactis biovar. diacetylactis  Cheeses are frequently made with natural whey starters (NWS). The whey from the previous cheese making is cultured and used for the next day. This practice, although essential for the development of typical sensory characteristics, can sometimes lead to acidification defects. In this work, the ability of Lactococcus lactis subsp. lactis biovar. diacetylactis to dominate over the other lactic acid bacteria (LAB) was tested in a controlled system as a possible explanation for these acidification breakdowns. A starter made of two Lc lactis subsp. lactis strains (LL), one Lc lactis subsp. cremoris strain (LC), and one Lc lactis subsp. lactis biovar. diacetylactis (LD) was added to sterilized milk. After incubation, the whey was removed and used to re-seed sterilized milk, the next day. This process was made during a five and twelve days' period. During the eight first days, the proportion of LD population increased, while the other LAB remained rather stable. Thereafter, LD strains dominated. At the same time, the diversity of LD population diminished considerably. If acidification ability of these LAB is not altered, this simplification was particularly hazardous in case of phages attack. LC and LL behavior was tested in milk containing increasing diacetyl concentrations. As long as diacetyl did not exceed a 5 ppm level — frequently measured in dairy products — its influence was impossible to detect. The selective advantage conferred by the citrate metabolism was proposed as a possible explanation for the LD population dominance. Other potential factors were also examined.
http://fst.sagepub.com/content/14/6/469.refs
http://genesis-bglab.com/eng/index.php?page=2&CID=16

Lc. lactis subsp. cremoris  MG1363, is the lactococcal strain most intensively studied throughout the world. It is a plasmid-free Lactococcus strain. It is not a natural inhabitant of the human gastrointestinal tract, but does survive passage through it, and has been used to deliver bioactive peptides to the gut. There are a number of mobile genetic elements in L. lactis MG1363, namely the unique sex factor, insertion elements, and the integration hotspot region. The latter enables L. lactis MG1363 to stably integrate laterally acquired DNA and has played a key role in the evolution of the genome of L. lactis MG1363 and related strains. It allowed L. lactis MG1363 to stably maintain a functional copy of the opp operon, which is essential for growth in milk. Forty seven of the genes present in L. lactis MG1363 but absent in L. lactis IL1403 are thought to be involved in carbohydrate metabolism and transport. Consequently L. lactis MG1363 displays a larger capability to grow on various sugars, especially those found in plant material, pointing to a plant associated biological niche for the ancestor of L. lactis MG1363. Lactococci are mesophilic lactic acid bacteria that were first isolated from green plants. However, today they are used extensively in food fermentations. These bacteria are selected for use in fermentations based on their metabolic stability, their resistance to bacteriophage, and their ability to produce unique compounds often from amino acid catabolism. The study of their physiology in adverse conditions such as low pH and high NaCl indicates that they adapt to these environments quickly and change their metabolism based on carbohydrate starvation. Recent genome studies and physical maps indicate that bacterial genomes are very dynamic. The importance of lactococci, specifically L. lactis subsp. cremoris, is demonstrated by its continual use in food fermentations. L. lactis subsp. cremoris strains are preferred over L. lactis subsp. lactis strains because of their superior contribution to product flavor via unique metabolic mechanisms.
http://genome.jgi-psf.org/laccr/laccr.home.html
http://expasy.org/sprot/hamap/LACLM.html

Enterococcus durans is Gram stain positive. Enterococcus durans is a facultative anaerobe. Enterococcus durans is non-motile. Bacteria; Firmicutes; Bacilli; Lactobacillales; Enterococcaceae; Enteroc. Enterococcus durans infection in poultry has been associated with bacteremia and encephalomalacia. Streptococcus durans is a synonym for Enterococcus durans. Enterococcus faecium can be misidentified as Enterococcus durans by some automated testing methods. It is unclear what the importance of Enterococcus durans in human infections as strains of Enterococcus faecium are frequently incorrectly identified as Enterococcus durans.
http://www.rci.rutgers.edu/~microlab/CLASSINFO/IMAGESCI/B.%20subtilis%20and%20E.htm
http://www.thelabrat.com/restriction/sources/Enterococcusdurans.shtml

Leuconostoc mesenteroides subsp. cremoris
Leuconostoc species are frequently used in mesophilic cultures to produce aroma during milk fermentations.Leuconostoc mesenteroides ssp. cremoris 91404 was selected as an aroma producer in preparation of experimental cultured buttermilk based on low diacetyl reductase activity, citrate utilization and high diacetyl production under acidic conditions, growth characteristics, and compatibility with Lactococcus strains. However, no diacetyl was detected in buttermilk that was made in the traditional commercial manner. Simple and direct GLC analysis without prior processing was applied to quantify volatile compounds in milk that had been fermented with Leu. mesenteroides ssp. cremoris and Lactococcus lactis ssp. cremoris. Fortification of ripened buttermilk with sodium citrate resulted in a significant increase of diacetyl and acetoin production during buttermilk storage (5°C for 2 wk). Surplus of citrate, low pH (pH 4.5 to 4.7), a sufficient number of active nongrowing aroma producers, air incorporation during curd breaking, and low temperature storage facilitated citrate metabolism toward production and conservation of flavor during 2 wk of storage. Incorporation of a ropy Lc. lactis ssp. cremoris strain 352 in starter culture significantly improved the texture and appearance of experimental cultured buttermilk.
http://www.magma.ca/~pavel/science/Leuconostoc.htm
http://www.journalofdairyscience.org/article/S0022-0302(97)75907-1/abstract

Leuc. mesenteroides subsp. mesenteroides
Leuconostoc species are epiphytic bacteria that are wide spread in the natural environment and play an important role in several industrial and food fermentations. Leuconostoc mesenteroides is a facultative anaerobe requiring complex growth factors and amino acids (Reiter and Oram 1982; Garvie 1986).

Most strains in liquid culture appear as cocci, occurring singly or in pairs and short chains, however, morphology can vary with growth conditions; cells grown in glucose or on solid media may have an elongated or rod shaped morphology. Cells are Gram positive, asporogenous and non-motile.

A variety of lactic acid bacteria (LAB), including Leuconostoc species are commonly found on crop plants (Mundt et al 1967; Mundt 1970). L. mesenteroides is perhaps the most predominant LAB species found on fruits and vegetables and is responsible for initiating the sauerkraut and other vegetable fermentations (Pederson and Albury 1969). L. mesenteroides starter cultures also used in some dairy and bread dough fermentations (Server-Busson et al. 1999).

Under microaerophilic conditions, a heterolactic fermentation is carried out. Glucose and other hexose sugars are converted to equimolar amount of D-lactate, ethanol and CO2 via a combination of the hexose monophosphate and pentose phosphate pathways (Demoss et al 1951; Garvie 1986; Gottschalk 1986). Other metabolic pathways include conversion of citrate to diacetyl and acetoin (Cogan et al 1981) and production of dextrans and levan from sucrose (Alsop 1983; Broker 1977).

Viscous polysaccharides produced by L. mesenteroides are widely recognized as causing product losses and processing problems in the production of sucrose from sugar cane and sugar beets (Tallgren et al. 1999). The first observation of the production of polysaccharide "slime" from sugar, dates to the earliest days of the science of microbiology; Pasteur (1861) attributed this activity to small cocci, presumably Leuconostoc species. Commercial production dextrans and levans by L. mesenteroides, for use in the biochemical and pharmaceutical industry, has been carried out for more than 50 years (Alsop 1983; Sutherland 1996).
Dextrans are used in the manufacture of blood plasma extenders, heparin substitutes for anticoagulant therapy, cosmetics, and other products (Leathers et al 1995; Sutherland 1996; Alsop 1983; Kim and Day 1994). Another use of dextrans is the manufacture of Sephadex gels or beads, which are widely used for industrial and laboratory protein separations (Sutherland 1996). Currently, L. mesenteroides has significant roles in both industrial and food fermentations.
http://www.morgboard.proboards.com/index.cgi?board=general&action=display&thread=824&page=11
http://genome.jgi-psf.org/leume/leume.home.html

Leuc. dextranicum  The constitutive mutants of Leuconostoc dextranicum NRRL B-1146 were generated by classical mutagenesis technique using UV radiation for higher production of glucan. The conditions of mutagenesis such as dilution factor and time of UV light exposure were optimized. Three stage screening of mutants was carried out and the mutants were grown and subsequently tested for glucan content produced after the second stage. In the first stage 137 mutants were picked by visual screening based on morphology and colony size and grown. In the second stage of screening, 97 colonies were visually screened from 137 colonies and glucan content was analysed by microtitre format. In the third stage screening, 11 higher glucan producing mutants were selected from 97. Finally, 3 mutants produced significantly high glucan content, out of 11 selected mutants. The wild-type strain gave 1.01 g/l of glucan using statistically optimized medium. The mutant 64 gave maximum glucan content of 5.1 g/l, 5 times higher than that produced by wild-type Leuconostoc dextranicum NRRL B-1146 followed by mutant 88 giving 4.24 g/l and mutant 9 giving 4.1 g/l.
http://coyoteuss.livejournal.com/50426.html
http://www.ispub.com/journal/the_internet_journal_of_microbiology/volume_7_number_1_31/article/mutagenesis-of-leuconostoc-dextranicum-nrrl-b-1146-for-higher-glucan-production.html