Lactic acid bacteria

Lactic acid bacteria
Light microscope image of a Lactobacillus species
Systematics
Domain : Bacteria (bacteria) Department : Firmicutes Class : Bacilli Order : Lactic acid bacteria
Scientific name
Lactobacillales
Ludwig et al. 2010

The lactic acid bacteria or Lactobacillales form an order of gram-positive , facultatively anaerobic , but mostly aerotolerant bacteria that break down carbohydrates into lactic acid ( lactic acid fermentation ).

Lactic acid bacteria occur in humans and animals. They colonize the digestive tract . They can also be found in milk . In large numbers, their lactic acid production leads to the thickening of the milk, the basis for the production of yoghurt , cheese and other milk products . In addition to the industrially used lactic acid bacteria, there are also pathogens in this order , e.g. B. some Streptococcus species ( streptococci ).

features

Lactic acid bacteria hardly resemble each other morphologically . There are representatives with cocci-shaped cells (in numerous genera from Aerococcus to Vagococcus ) as well as representatives whose cells appear rod-shaped , with different lengths. The genera whose cells are typically rod-shaped include u. a. Lactobacillus and Carnobacterium . In addition, there are more oval or ovoid ("egg-shaped") cell shapes, which are typical of Leuconostoc and Oenococcus . The genus Weissella has both ovoid and rod-shaped cells.

All lactic acid bacteria are gram-positive bacteria and cannot form endospores . As representatives of the Firmicutes , they belong to the bacteria with a low GC content , i.e. a low proportion of guanine and cytosine in the bacterial DNA . The GC content of many genera is in the range from 34 to 46  mol percent , but values ​​above 50 mol percent have also been determined for representatives of the genus Lactobacillus .

Light microscope image of Enterococcus faecalis , single or paired cocci can be seen .

They can be uniformly described on the basis of their physiological characteristics. Your metabolism and energy change is chemo - heterotrophic . They are dependent on carbohydrates for energy production , which they use in a fermentation process . This fermentative metabolism is characterized by the fact that the substrates are broken down without oxygen . The typical fermentation product for lactic acid bacteria is lactic acid , which is why this metabolic pathway is called lactic acid fermentation . According to the products that result from lactic acid fermentation, a distinction can be made as follows:

• Homofermentative types produce almost exclusively (> 90%) lactic acid or lactate , the anion of lactic acid , as the end product . This metabolic pathway is therefore called homofermentative lactic acid fermentation . These include representatives of the genera Enterococcus , Lactococcus , Pediococcus and Streptococcus .
• In addition to lactic acid, heterofermentative species also produce a significant proportion of other end products, mostly ethanol and carbon dioxide , sometimes acetic acid . The heterofermentatives usually lack the enzyme aldolase . Their metabolic pathway is called heterofermentative lactic acid fermentation . These include representatives of the genera Carnobacterium , Leuconostoc and Weissella .

The representatives of the genus Lactobacillus do not form a uniform group in this regard.

Lactic acid bacteria differ from other bacteria that also produce lactic acid in that they are only able to ferment in terms of metabolism , which they also carry out in the presence of oxygen. They can multiply in the presence and absence of oxygen, the metabolism is thus described as facultatively anaerobic . Due to their specialization in the growth in milk and similar nutrient and supplin-rich environments, lactic acid bacteria have lost the ability to biosynthesize many vital substances, such as amino acids and the porphyrins and cytochromes necessary for respiratory processes . Among other things, they do not form catalase .

Occurrence and ecology

With regard to their need for nutrients such as carbohydrates, amino acids, vitamins and other supplines, lactic acid bacteria can be characterized as demanding. They also prefer habitats with low oxygen saturation .

Nevertheless, lactic acid bacteria are almost ubiquitous . They can be found in the intestines or in the mucous membranes of mammals . In humans, lactic acid bacteria are mainly found in the digestive tract - including the oral cavity and intestines - as well as in the vagina (called Döderlein bacteria after the discoverer ). In pigs , cattle , dogs , mice , rats , chickens and other animals they were considered part of the intestinal flora established. Even in the stomach by honey bees and frogs they occur. They can also be found in living or decomposing plants, in milk and in all places that come into contact with milk. They were also found in sewage . Some representatives prefer a marine habitat.

If one looks at the habitats from the point of view of food or feed , numerous examples can be found in which the lactic acid bacteria are involved in a “desired” fermentation, such as yogurt , cheese , sourdough , sauerkraut , raw sausage or silage . On the other hand, their presence also leads to microbial spoilage of many foods, for example beer , wine and cider or meat and meat products . It should also be noted that many lactic acid bacteria can also grow in an acidic environment, i.e. at low pH values . They can be involved in the spoilage of fruit juices or foods preserved with vinegar .

Their lactic acid fermentation lowers the pH value in the habitat of the lactic acid bacteria. In the case of many other bacteria, this means that they can no longer multiply there. Among other things, clostridia , listeria or coliform bacteria are inhibited in growth. This effect turns out to be positive in the production of food or feed.

Systematics

Historical development

The systematics of lactic acid bacteria has changed significantly since the second half of the 20th century. In the 1960s, the lactic acid bacteria were assigned to the Lactobacteriaceae family . In the 1980 Approved Lists of Bacterial Names based on the newly organized Bacteriological Code , however, this family is not listed, instead the Lactobacillaceae family is included. But even later this outdated system of the Lactobacteriaceae family was still used in part. In the Approved Lists of Bacterial Names from 1980 there are also the Lactobacilleae with the type genus Lactobacillus in the tribus rank , which is based on botany and which is no longer used in the bacterial system . The lactic acid bacteria were first established as a separate order by Wolfgang Ludwig , who, together with Karl-Heinz Schleifer and William B. Whitman, created the Lactobacillales ord. nov. in Bergey's Manual of Systematic Bacteriology (2009 edition), with “ord. nov. ”for ordo novus ( Latin for“ new order ”). Through the publication in the Validation List no.132 , the order Lactobacillales was recognized in 2010 according to the rules of the Bacteriological Code.

The ordinal name is derived from the type genus Lactobacillus , with the typical ending -ales, whereby lactis stands from the Latin for "milk" and refers to the occurrence of lactic acid bacteria. The Germanized name Laktobazillen refers to members of the genus Lactobacillus and should therefore not be used for the Lactobacillales.

The exact system of lactic acid bacteria is partly controversial. The Oscillospiraceae family can be found in various sources. B. in the important reference work of the phylogenetic systematics of prokaryotes, Bergey's Manual of Systematic Bacteriology (2004 edition) is not listed.

Current system

There are currently six families with a total of around 40 genera belonging to the order Lactobacillales; some genera are named as examples for each family (as of 2014):

• Aerococcaceae Ludwig et al. 2010
  • Aerococcus Williams et al. 1953 (family type)
  • Facklamia Collins et al. 1997
• Carnobacteriaceae Ludwig et al. 2010
  • Alkalibacterium Ntougias & Russell 2001
  • Carnobacterium Collins et al. 1987 (family type)
  • Marinilactibacillus Ishikawa et al. 2003
  • Trichococcus Scheff et al. 1984 emend. Liu et al. 2002
• Enterococcaceae Ludwig et al. 2010
  • Enterococcus (ex Thiercelin & Jouhaud 1903) Schleifer & Kilpper-Bälz 1984 (type genus of the family)
  • Vagococcus Collins et al. 1990
• Lactobacillaceae Winslow et al. 1917
  • Lactobacillus Beijerinck emend in 1901. Cai et al. 2012. (type genus of the family and the order)
  • Pediococcus Claussen 1903
• Leuconostocaceae Grinder 2010
  • Leuconostoc van Tieghem 1878 (type genus of the family)
  • Weissella Collins et al. 1994 emend. Padonou et al. 2010
• Streptococcaceae Deibel & Seeley 1974
  • Lactococcus Schleifer et al. 1986
  • Streptococcus Rosenbach 1884 (type genus of the family)

The genus Acetoanaerobium is included in incertae sedis .

Important representatives

The following species and subspecies , for example, are of importance to humans :

• Enterococcus faecalis - a harmless resident of the human intestine
• Lactobacillus acidophilus - part of the normal vaginal flora
• Lactobacillus casei - part of probiotics
• Lactobacillus crispatus and Lactobacillus iners - the most important components of the normal vaginal flora
• Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus salivarius subsp. thermophilus - used for yoghurt production
• Lactobacillus helveticus - for cheese production
• Lactobacillus sanfranciscencis and Lactobacillus plantarum - for sourdough production
• Lactococcus lactis - for the production of cream cheese and sour cream products
• Leuconostoc mesenteroides - used toextract sauerkraut
• Oenococcus oeni - is used in wine production
• Streptococcus pyogenes - pathogens a . a. from purulent tonsillitis
• Weissella viridescens - involved in the spoilage of meat , especially its green color

meaning

Importance to humans

→ Main article : Importance of the Lactobacillaceae for humans

Lactic acid bacteria are among the most important representatives of the human intestinal flora and the vaginal flora . Some species are pathogenic , so they can cause disease, including several Streptococcus species. Streptococcus pneumoniae is a pathogen that u. a. cause pneumonia; Streptococcus mutans and Streptococcus sobrinus are involved in the development of dental caries . Lactic acid bacteria can become trapped in skin cells and turn them into multipotent cells.

The industrial use of Lactobacillales is of great importance for humans. Various species, subspecies and strains of bacteria are used for preservation of food used for. B. yogurt , kefir , sour milk , cheese but also in sauerkraut , in kimchi and when baking z. B. in sourdough . They are also used for skin care and caries prophylaxis .

Some lactic acid bacteria are used as probiotics . The advertisements attribute a special effect to the regular consumption of products containing Lactobacillus casei or Lactobacillus acidophilus .

Meaning in milk

For the milk processing industry, lactic acid bacteria are a criterion for quality. Cow milk delivered to the dairy (delivery milk ) is divided into EU quality classes according to the milk quality regulation : If there are less than 100,000 germs / ml, the milk corresponds to quality class 1, above that to quality class 2. These average germ counts are recorded over a longer period of time. For a long time it has been possible to assume an average of 20,000 germs / ml milk. If the cows udder is brushed by hand at the beginning of milking , this milk can often be lower in germs than that of cows that are milked fully automatically. Milk that is milked under aseptic conditions as possible contains less than 1,000 germs / ml.

In a warm environment (20 to 30 ° C), untreated milk becomes acidic with around one million bacteria per milliliter after around ten hours. The acid precipitates the milk protein so that the milk thickens, known as curdling . Therefore, preferred milk is reduced to max. 6 ° C as this inhibits bacterial growth.

literature

• Martin Dworkin et al. a. (Ed.): The Prokaryotes. A Handbook on the Biology of Bacteria . 3. Edition. tape 4 : Bacteria: Firmicutes, Cyanobacteria . Springer, New York 2006, ISBN 978-0-387-25494-4 .
• Paul de Vos et al. a. (Ed.): Bergey's Manual of Systematic Bacteriology . 2nd Edition. tape 3 : The Firmicutes . Springer, New York 2009, ISBN 978-0-387-95041-9 .

Web links

Commons : lactic acid bacteria ( Lactobacillales )  - collection of pictures, videos and audio files

• Allergy prevention through lactic acid bacteria

Individual evidence

1. ↑ ^{a b c d} Jean Euzéby, Aidan C. Parte: Order Lactobacillales. In: List of Prokaryotic names with Standing in Nomenclature ( LPSN ). Retrieved July 20, 2014 .  
2. ↑ ^{a b c d e f} Walter P. Hammes, Christian Hertel: The Genera Lactobacillus and Carnobacterium. In: The Prokaryotes. A Handbook on the Biology of Bacteria . Volume 4: Bacteria: Firmicutes, Cyanobacteria . Edited by M. Dworkin u. a. 3. Edition. Springer, New York 2006, ISBN 978-0-387-25494-4 , pp. 320-403
3. ↑ ^{a b c d e f} Johanna Björkroth, Wilhelm Holzapfel: Genera Leuconostoc, Oenococcus and Weissella. In: M. Dworkin u. a. (Ed.): The Prokaryotes. A Handbook on the Biology of Bacteria . Volume 4: Bacteria: Firmicutes, Cyanobacteria . 3. Edition. Springer, New York 2006, ISBN 978-0-387-25494-4 , pp. 267-319.
4. ↑ ^{a b c d} Michael T. Madigan, John M. Martinko, Jack Parker: Brock Mikrobiologie. German translation edited by Werner Goebel. Spektrum Akademischer Verlag, Heidelberg / Berlin 2000, ISBN 978-3-8274-0566-1 , pp. 558-563, 693.
5. ^ ^{A b c} Hans G. Schlegel, Christiane Zaborosch: General microbiology . 7th edition. Thieme, Stuttgart / New York 1992, ISBN 3-13-444607-3 , p. 296-299 .
6. ↑ ^{a b} Gerhard Eisenbrand, Peter Schreier (Ed.): Römpp Lexikon der Lebensmittelchemie . 2nd Edition. Thieme, Stuttgart / New York 2006, ISBN 978-3-13-736601-0 , p. 741–745 ( limited preview in Google Book search).
7. ↑ M. Ishikawa, K. Nakajima et al. a .: Marinilactibacillus psychrotolerans gen. nov., sp. nov., a halophilic and alkaliphilic marine lactic acid bacterium isolated from marine organisms in temperate and subtropical areas of Japan. In: International journal of systematic and evolutionary microbiology , Volume 53, No. 3, May 2003, pp. 711-720, ISSN  1466-5026 . PMID 12807191 .
8. ↑ William MO Leary: decenoic, Dodecenoic, and Tetradecenoic Acids in the Lactobacteriaceae. In: Biochemistry , Vol. 4, No. 8, August 1965, pp. 1621-1627, ISSN  0006-2960 . doi: 10.1021 / bi00884a025 .
9. ↑ Lactic acid bacteria. In: Compact lexicon of biology at Spektrum.de. Retrieved July 20, 2014 .  
10. ↑ ^{a b} Approved Lists of Bacterial Names . In: VBD Skerman, Vicki McGowan, PHA Sneath (Eds.): International Journal of Systematic Bacteriology . tape  30 , no. 1 , 1980, p. 225-420 , doi : 10.1099 / 00207713-30-1-225 ( sgmjournals.org [PDF; accessed April 13, 2014]). sgmjournals.org ( Memento from January 22, 2013 in the Internet Archive )
11. ^ W. Ludwig, K.-H. Schleifer, WB Whitman: Order II. Lactobacillales ord. nov. In: Bergey's Manual of Systematic Bacteriology . 2nd Edition. tape 3 : The Firmicutes . Springer, New York 2009, ISBN 978-0-387-95041-9 .
12. ↑ Jean Euzéby: List of new names and new combinations previously effectively, but not validly, published - Validation List no. 132. In: International Journal of Systematic and Evolutionary Microbiology , Volume 60, No. 3, March 2010, p. 469– 472, doi: 10.1099 / ijs.0.022855-0 .
13. ↑ George M. Garrity et al. a .: Taxonomic Outline of the Prokaryotes. Bergey's Manual of Systematic Bacteriology . 2nd edition, Release 5.0. Springer-Verlag, New York 2004 ( uni-muenster.de ( memento from June 17, 2012 in the Internet Archive ; PDF; 3.3 MB)).
14. ↑ K. Ohta, R. Kawano, N. Ito: Lactic acid bacteria convert human fibroblasts to multipotent cells. In: PloS one , Volume 7, No. 12, 2012, p. E51866, ISSN  1932-6203 . doi: 10.1371 / journal.pone.0051866 . PMID 23300571 . PMC 3530539 (free full text).
15. ↑ BASF pro-t-action ™ Lactobacillus anti-caries for oral hygiene ( Memento of the original dated February 2, 2011 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. 
16. ↑ Germ count statistics. (No longer available online.) In: Website Milchprüfring Baden-Württemberg e. V. Archived from the original on July 27, 2014 ; Retrieved July 21, 2014 .  
17. ↑ Milk quality in Bavaria. (No longer available online.) In: Website Landesvereinigung der Bayerischen Milchwirtschaft e. V. Archived from the original on December 27, 2013 ; Retrieved July 21, 2014 .