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Michelle's Notes

Page history last edited by Michelle 15 years, 7 months ago

Structure

Source:

"HAMAP: Leuconostoc mesenteroides subsp. mesenteroides (strain ATCC 8293 / NCDO 523) complete proteome." Expasy. SIB Switzerland. 9 Dec. 2008 <http://www.expasy.ch/sprot/hamap/LEUMM.html>.

 

 

Quote:

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. It is asporogenous and non-motile. Most strains in liquid culture appear as cocci, however, cells grown in glucose or on solid media may have an elongated or rod shaped morphology. A variety of lactic acid bacteria (LAB), including Leuconostoc species are commonly found on crop plants. 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. L. mesenteroides starter cultures also used in some dairy and bread dough. Under microaerophilic conditions, a heterolactic fermentation is carried out.

Paraphrase:

Leuconostoc Mesenteroides has a pretty simple structure to it. When tested in a liquid culture, Leuconostoc Mesenteroides appears to be cocci shaped, but when it’s tested in glucose or a solid media, it is shown as an elongated rod shape, and it always stays together in chains. It is even sometimes found to be in the shape of bacilli, but this is quite uncommon. It is an anaerobic bacteria, meaning it doesn’t require oxygen to function. It is also a lactic acid bacteria (LAB), non-spore forming, and it’s a non-motile bacteria.


Uses

Source:

"HAMAP: Leuconostoc mesenteroides subsp. mesenteroides (strain ATCC 8293 / NCDO 523) complete proteome." Expasy. SIB Switzerland. 9 Dec. 2008 <http://www.expasy.ch/sprot/hamap/LEUMM.html>.

 

 

Quote:

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. Other metabolic pathways include conversion of citrate to diacetyl and acetoin and the production of dextrans and levan from sucrose. 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. Dextrans are used in the manufacture of blood plasma extenders, heparin substitutes for anticoagulant therapy, cosmetics, and other products. Another use of dextrans is the manufacture of Sephadex gels or beads, which are widely used for industrial and laboratory protein separations. Thus L. mesenteroides has significant roles in both industrial and food fermentations. Interestingly 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. 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


General Facts

Source:

"Leuconostoc citreum, Leuconostoc cremoris." Foods Under the Microscope. 20 Apr. 2006. SCIMAT. 11 Dec. 2008 <http://www.magma.ca/~pavel/science/Leuconostoc.htm>.

Quote:

As this WinWord DOC file explains, the genus Leuconostoc belongs to the group of lactic acid bacteria. They are a group of related Gram-positive, non-sporulating bacteria that produce lactic acid as a result of carbohydrate fermentation. Milk provides a good substrate for microorganisms that further improve nutrition, texture and flavor characteristics of a wide variety of foods. Lactic acid bacteria are used in the production of fermented food products, such as yogurt (Streptococcus spp. and Lactobacillus spp. and other milk products (Lactococcus spp.), and sausages. However, fermented milk products also contain Leuconostoc spp. bacteria (e.g., L. cremoris, L. citrovorum (L. mesenteroides subsp. cremoris, and L. dextranicum) which impart characteristic flavour. They are used as part of bacterial starter cultures needed in the manufacture of dairy products. L. mesenteroides subsp. cremoris is used in cultured buttermilk and cultured sour cream. A variety of Leuconostoc strains is present in kefir.

Paraphrase:

L. Mesenteroides is:

a lactic acid bacteria, gram-positive, non-sporulating, causes fermentation, creates lactic acid, can grow on milk, improves texture, nutrition, and flavor in many foods.

 


Lactic Acid Bacteria

Source:

"Leuconostoc citreum, Leuconostoc cremoris." Foods Under the Microscope. 20 Apr. 2006. SCIMAT. 11 Dec. 2008 <http://www.magma.ca/~pavel/science/Leuconostoc.htm>.

Quote:

Like the lactic acid bacteria, leuconostocs need complex media due to their multiple demands for amino acids, peptides, carbohydrates, vitamins and metallic ions. They represent about 12% of lactic acid bacteria isolated from various ecosystems, mostly from plant materials. Some may be isolated from the surfaces of a wide range of healthy vegetables and fruits, including grapes.

Paraphrase:

need amino acids, peptides, carbohydrates, vitamins, and metallic ions

 


Fermentation

Source:

"Leuconostoc citreum, Leuconostoc cremoris." Foods Under the Microscope. 20 Apr. 2006. SCIMAT. 11 Dec. 2008 <http://www.magma.ca/~pavel/science/Leuconostoc.htm>.

Quote:

Sauerkraut fermentation relies on naturally occurring Leuconostoc spp. bacteria present on fresh cabbage leaves. Leuconostoc mesenteroides is the bacterium associated with the sauerkraut and pickle fermentations. It initiates the desirable lactic acid production in these products. Translated from German, "sauerkraut" means "sour cabbage". Lactic acid and the kitchen salt used produce an environment more favourable for Leuconostoc than other bacteria and, consequently, unwelcome coliform bacteria rapidly decline. Additional probiotic microrganisms are also involved in the production of sauerkraut. They multiply in large quantities in the juice.

Paraphrase:

L. Mesenteroides causes cabbage to ferment, forming sauerkraut. Same with giving pickles their sour taste.

-initiates the lactic acid production


Testing

Source:

"Isolation and Characterization of Leuconostoc Mesenteroides From Cheese 3." Science Ray. 23 Aug. 2008. Triond. 12 Dec. 2008 <http://www.scienceray.com/Biology/Microbiology/Isolation-and-Characterization-of-Leuconostoc-Mesenteroides-From-Cheese-3.223313>.

Quote:

S.No

Cultural & Biochemical characteristics

Results

1

Gram's staining

Gram positive, coccobacilli, with rounded ends.

2

Motility

Motile

3

Capsule staining

Non-capsulated

4

Spore staining

Non-sporing

5

Growth at 37oC

+

6

Growth at 30oC

+

7

Growth at 4oC

+

On MRS medium:

   

8

At 37oC

Pale yellow colored, smooth, slimy, entire marginated, convex colonies.

9

At 4oC

In refrigeration, colonies turned white, and slow growth was observed.

10

On MacConkey agar medium

Lactose fermenting, pink colored colonies.

11

On blood agar medium

Non-hemolytic, colorless colonies.

     

Biochemical tests:

   

12

Indole

-

13

Methyl red

-

14

Voges Proskauer

+

15

Citrate

-

16

Urease

-

17

Arginine

 

-

 

Carbohydrate fermentation tests:

   

18

Glucose

 

+ (acid and gas)

 

19

Arabinose

+

20

Lactose

+

21

Mannitol

-

22

Sucrose

+

23

Dextrose

+

24

Maltose

+


Lactic Acid

Source:

Stanley, Peter. "Lactic acid: who needs it? What do sour milk, yoghurt and muscle cramp have in common? Answer: the presence of lactic acid. (molecule)." Biological Sciences Review Nov. 2005: 6. Science Resource Center. Gale. St. Andrew's Upper School Library, Austin, TX. 7 Dec. 2008 <http://infotrac.galegroup.com/itweb/?db=SciRC>.

Quote:

Lactic acid is formed by anaerobic respiration. This happens in a variety of cells, including skeletal muscle, red blood cells and several microorganisms. The production of lactic acid can be welcome or unwelcome. In food manufacture it is responsible for the tangy flavour of yoghurt and contributes to the flavour of cheese. On the other hand, it is responsible for the taste of sour milk and contributes to the painful condition of muscle cramp when we exercise too vigorously.

 

Lactic acid has the chemical formula C[H.sub.3]CHOHCOOH--half a glucose molecule. It is soluble in water and is a weak acid in aqueous solution. At the pH of the cytoplasm of cells (pH 6.8), lactic acid exists primarily as the lactate anion (C[H.sub.3]CHOHCO[O.sup.-]), the charge being balanced mainly by potassium ions ([K.sup.+]).


Lactic Acid in Muscle

Source:

Stanley, Peter. "Lactic acid: who needs it? What do sour milk, yoghurt and muscle cramp have in common? Answer: the presence of lactic acid. (molecule)." Biological Sciences Review Nov. 2005: 6. Science Resource Center. Gale. St. Andrew's Upper School Library, Austin, TX. 7 Dec. 2008 <http://infotrac.galegroup.com/itweb/?db=SciRC>.

Quote:

Muscle contraction requires energy. The immediate source of this energy is ATE which releases energy when it is broken down to ADP and phosphate by hydrolysis. ATP cannot be stored in tissues in any significant amounts, so it must be continuously synthesised. If the work performed by skeletal muscles during exercise is such that the demand for oxygen for aerobic respiration exceeds supply, anaerobic respiration will occur. This results in build-up of lactic acid in the muscle (see Box 3 on p. 8). This happens in the first minute or so of moderate to hard exercise, before the cardiovascular system has had time to increase blood flow, and hence oxygen supply, to the muscles. This is why anaerobic respiration is the main provider of energy in competitions such as a 400 m race, which generally lasts for less than 1 minute. Over longer distances, such as 1500 m, there is enough time for the cardiovascular system to adjust and divert more blood to skeletal muscles, so that aerobic respiration takes over as the dominant provider of energy.


Lactic Acid in foods

Source:

Stanley, Peter. "Lactic acid: who needs it? What do sour milk, yoghurt and muscle cramp have in common? Answer: the presence of lactic acid. (molecule)." Biological Sciences Review Nov. 2005: 6. Science Resource Center. Gale. St. Andrew's Upper School Library, Austin, TX. 7 Dec. 2008 <http://infotrac.galegroup.com/itweb/?db=SciRC>.

Quote:

The production of yoghurt from milk is a fermentation reaction. The starter culture contains two species of bacteria which form a mutualistic association--each helps the other to grow. First, the bacterium Lactobacillus bulgaricus hydrolyses milk protein to smaller polypeptides and amino adds. It also breaks down lactose to form lactic acid, along with some ethanal. The amino acids stimulate growth of a second bacterium--Streptococcus thermophilus. This produces methanoic acid, which in turn stimulates growth of L. bulgaricus. At the end of fermentation, the lactic acid concentration is about 1.4% and the pH has decreased to about 4.5. This moderately acidic pH level is primarily due to the accumulation of lactic acid and has a number of advantages. First, it inhibits further bacterial metabolism, thereby helping to preserve the yogurt and reduce the rate of spoilage. Second, it denatures the milk protein, causing coagulation of the protein and hence a thickening of the yoghurt. Third, the lactic acid, along with ethanol and some other organic acids and aldehydes produced in fermentation, contributes to the tangy flavour of the yoghurt.

Manufacture of cheese from milk also involves the production of lactic acid by bacteria. The mixture of different species of bacteria used depends on the type of cheese produced and the fermentation conditions. For example, in the manufacture of cheddar cheese the starter culture is a mixture of several strains of Streptococcus lactis and Streptococcus cremoris. The lactose in the milk is hydrolysed to glucose and galactose, and anaerobic respiration breaks down the glucose to lactic acid. The low pH caused by the lactic acid coagulates the milk protein (mostly casein). This results in a separation of the milk into a solid component containing protein (curds) and a liquid component (whey). The curds are then processed further and allowed to ripen to form cheese. Accumulation of lactic acid also contributes to the flavour of the cheese.

Lactic acid is also produced during the manufacture of sauerkraut by fermentation of cabbage under anaerobic conditions. The fermentation is carried out by various species of bacteria naturally present in the cabbage, so no starter culture is required. Salt is added to favour the growth of lactic-acid-producing bacteria. Sugars such as glucose and fructose in the cabbage are broken down anaerobically by the bacterium Leuconostoc mesenteroides to form lactic add. Some of the by-products produced by this first reaction are then used by the bacterium Lactobacillus plantarum, which results in further production of lactic acid. The final product contains lactic acid at a concentration of about 1.7% and has a pH of about 3.5.

Gram Staining

Source:

Xu, George. "History of the Gram Stain and How it Works." Education and Training. 31 Oct. 1997. University of Pennsylvania Health System. 11 Dec. 2008 <http://health.upenn.edu/bugdrug/antibiotic_manual/Gram1.htm>.

Quote:

The Gram staining method, named after the Danish bacteriologist who originally devised it in 1882 (published 1884), Hans Christian Gram, is one of the most important staining techniques in microbiology. It is almost always the first test performed for the identification of bacteria. The primary stain of the Gram's method is crystal violet. Crystal violet is sometimes substituted with methylene blue, which is equally effective. The microorganisms that retain the crystal violet-iodine complex appear purple brown under microscopic examination. These microorganisms that are stained by the Gram's method are commonly classified as Gram-positive or Gram non-negative. Others that are not stained by crystal violet are referred to as Gram negative, and appear red.

Paraphrase:

discovered in 1882 by Hans Christian Gram

first test performed on bacteria when trying ot identify it

stains the bacteria with a crystal violet stain

       -positive: retains the stain and turns violet

      -negative: is not stained and turns red

 

 


 

 

How Gram Staining works

Source:

Xu, George. "History of the Gram Stain and How it Works." Education and Training. 31 Oct. 1997. University of Pennsylvania Health System. 11 Dec. 2008 <http://health.upenn.edu/bugdrug/antibiotic_manual/Gram1.htm>.

Quote:

Gram staining is based on the ability of bacteria cell wall to retaining the crystal violet dye during solvent treatment. The cell walls for Gram-positive microorganisms have a higher peptidoglycan and lower lipid content than gram-negative bacteria. Bacteria cell walls are stained by the crystal violet. Iodine is subsequently added as a mordant to form the crystal violet-iodine complex so that the dye cannot be removed easily. This step is commonly referred to as fixing the dye. However, subsequent treatment with a decolorizer, which is a mixed solvent of ethanol and acetone, dissolves the lipid layer from the gram-negative cells. The removal of the lipid layer enhances the leaching of the primary stain from the cells into the surrounding solvent. In contrast, the solvent dehydrates the thicker Gram-positive cell walls, closing the pores as the cell wall shrinks during dehydration. As a result, the diffusion of the violet-iodine complex is blocked, and the bacteria remain stained. The length of the decolorization is critical in differentiating the gram-positive bacteria from the gram-negative bacteria. A prolonged exposure to the decolorizing agent will remove all the stain from both types of bacteria. Some Gram-positive bacteria may lose the stain easily and therefore appear as a mixture of Gram-positive and Gram-negative bacteria (Gram-variable).

Paraphrase:

Gram positive: higher peptidoglycan, less lipids, thicker cell wall

when crystal violet iodine is added to the cell wall, it's added as a mordant and therefore cannot be removed easily

the next step is adding a decolorizer, which dissolves the lipid layer in gram-negative cells, allowing the stain to diffuse into the surrounding solvent, so the violet color isn't concentrated. however, in gram-positive cells, the decolorizer dehydrates the cell, blocking the pores so the violet stain cannot diffuse, causing it to stay the crystal violet color.  

 

 

 

 

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