Lactobacillus rhamnosus
Lactobacillus rhamnosus is a probiotic lactic acid bacterium to be used in probiotics. It was formerly regarded as a subspecies of Lactobacillus casei. The species includes many tribes. The genome of a strain was completely sequenced in 2009.
- 3.1 Outer systematics
- 3.2 Internal systematics
- 3.3 Etymology
Features
Appearance
Lactobacillus rhamnosus is a Gram-positive medium- long, rod-shaped bacterium. A single cell is 2.0-4.0 microns long and 0.8-1.0 microns wide. In light microscopic image to see individual cells and cell chains. The bacterium does not possess flagella for active movement and can not form Überdauerungsformen as endospores.
Growth and metabolism
L. rhamnosus is a typical representative of the genus Lactobacillus, it grows anaerobically, but aerotolerant. Temperatures usually used for the cultivation in the range of 30-37 ° C. Bacterium characterized by its tolerance to a wide temperature range from, growth is carried out also at 15 ° C ( in some strains even at 10 ° C ) and also at 45 ° C.
L. rhamnosus is included in the group 3 (Lactobacillus brevis group ) of the lactobacilli. For them, the heterofermentative lactic acid fermentation is typical. Glucose is fermented to L-( )- lactic acid, other fermentation products are carbon dioxide and ethanol. Addition of D-glucose L. rhamnosus can also utilize a number of other carbohydrates, such as monosaccharides, D-fructose, D-mannose, D -tagatose, galactose, ribose, and rhamnose ( indicated in the style name ). Furthermore, the sugar alcohols mannitol and sorbitol can be reduced, and some disaccharides, such as lactose (milk sugar), maltose, trehalose and cellobiose.
Some enzymes used in the metabolism, in order to reduce certain substrates are detected in a "Bunte number " to identify a bacterium. Here it is noticeable that Lactobacillus rhamnosus does not have many of these enzymes. He has neither catalase nor oxidase. Nor it has the enzyme urease, which enables the degradation of urea, nor arginine dihydrolase, ammonia to cleave from the amino acid arginine. The enzyme β -galactosidase is present, and allows the growth in milk, utilization of the milk sugars contained therein, it is also able to hydrolyse, esculin.
Genetics
The genome of numerous strains of the bacterium has been completely sequenced. The first sequencing was carried out in 2009 on Lactobacillus rhamnosus GG ATCC 53103rd The genome has a size of 3010 kilobase pairs (kb ), which is about 65 % of the genome size of Escherichia coli, but significantly more than in Lactobacillus delbrueckii subsp. bulgaricus (1865 kb). There are 2913 proteins annotated. In the following years further strains were genetically analyzed, with similar results. The tested bacterial strains were from human faeces, but it starter cultures used were also examined in the dairy industry.
The results of sequencing show a GC content ( the fraction of nucleic bases guanine and cytosine) in the bacterial DNA of about 47 mole percent, which is comparable to the GC content of L. delbrueckii ( 49-51 mole percent) and significantly greater than that of L. acidophilus, the GC content of DNA is 34 to 37 mole percent.
Pathogenicity
By Biostoffverordnung in connection with the TRBA 466 L. rhamnosus is assigned to risk group 2. Microorganisms in this risk group are defined in the Biostoffverordnung as " biological substances that can cause human disease and might be a hazard to workers [ ... ] ." However, non-pathogenic strains of L. rhamnosus be long been used in the food industry. This fact is taken into account by noting it in the classification in risk group 2 strains that have already been handled for many years safely in technical applications, are classified in risk group 1. In rare cases have been reported caused by the bacterium endocarditis.
Occurrence
L. rhamnosus is present in milk and milk products, including human feces and sewage it was detected. At times, his appearance is in the gut - as part of the intestinal flora in humans - detectable, so it is not a permanent intestinal inhabitants.
System
Outer systematics
L. rhamnosus was formerly regarded as a subspecies of Lactobacillus casei subsp casei rhamnosus and L. as indicated. Studies from 1989 showed that significant differences from other L. casei subspecies exist in the chemotaxonomic characteristics. The genetic studies using DNA -DNA hybridization confirmed significant differences, then L. rhamnosus was defined as an own species.
Inside systematics
From the way more than 20 strains of bacteria are known whose genome has been studied by DNA sequencing already partially. As type strain L. rhamnosus ATCC 7469 ( = NCDO 243) is considered.
Etymology
The genus name can be attributed to the presence and appearance of the bacterial cells, lac from the Latin meaning milk while bacillus (Latin ) refers to the rod- like shape. The species name refers to the ability of the bacterium to degrade the monosaccharide rhamnose.
Importance
Lactobacillus rhamnosus is a probiotic lactic acid bacterium. The bacterium is used for the relief of antibiotic- associated diarrhea. In children, a positive effect is thought to respiratory infections. In addition, the bacterium has a positive effect on the human urogenital system, there by protecting against pathogens.
An inserted in probiotics bacteria strain is Lactobacillus rhamnosus DR20. With him was studied in a long-term test how the composition of the intestinal flora in humans altered when the probiotic preparation is consumed regularly. The study published in 2000 concluded that L. rhamnosus during the phase of daily consumption in the faeces is detectable, so is part of the intestinal flora. This temporary occurrence in the gut (and thus in the feces ) is explained by the consumption of the probiotic, the bacteria thus pass through the intestine. Such strains are considered allochthonous bacteria, while autochthonous bacteria are regularly detected within each habitat. It was also noted that during the test phase changed the composition of the population of lactobacilli, and also increases the number of enterococci. However, these effects are only temporary, and at the end of the 3 -month period in which the probiotic was not consumed, no longer clearly visible.
The desired of the probiotic lactic acid bacteria -promoting effect on the immune system was tested in animal experiments on mice and it was confirmed. The extent to which these results are transferable to humans, is part of the discussion about the health benefits of probiotics.