Lactococcus

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Lactococci
Lactococcus lactis (after Gram stain)

Lactococcus lactis (after Gram stain )

Systematics
Domain : Bacteria (bacteria)
Department : Firmicutes
Class : Bacilli
Order : Lactic acid bacteria (Lactobacillales)
Family : Streptococcaceae
Genre : Lactococci
Scientific name
Lactococcus
Schleifer et al. 1986

Lactococcus is the name of a genus of gram-positive , spherical bacteria fromthe Streptococcaceae family . His name is " Germanized " also written as Laktokokkus ( plural : Laktokokken ). Lactococcus belongs together with other bacterial genera to the order of the lactic acid bacteria ; they all produce lactic acid through fermentation .

Lactococcus - types are important for the food industry. They are used for the production of acidified milk products . As a rule, they do not harm people themselves, they are apathogenic .

The species of the genus Lactococcus were assigned to the genus Streptococcus until 1986 . The division of the genus Streptococcus into the genera Streptococcus (more pathogenic species) and Lactococcus (more "useful" species) took place in 1986. Often, species of the genus Lactococcus are still included in the genus Streptococcus .

features

Appearance

The representatives of the genus are gram-positive bacteria, they do not form persistent forms like endospores and in most cases are not capable of active movement . The cells of Lactococcus are round ( cocci ) and less than 2  micrometers (microns) in size. The cells are arranged in chains. Since such an arrangement is called streptococci, this has also been applied to lactococci.

The cells grow into colonies on solid, carbohydrate-containing nutrient media. In Lactococcus , these are usually colorless to white and typically quite small, their diameter is less than 1  mm .

Growth and metabolism

As representatives of the lactic acid bacteria , lactococci grow anaerobically and are aerotolerant, i. H. they grow in the presence of oxygen, but do not need oxygen for their metabolism . They are catalase negative and oxidase negative. However, they are able to form cytochromes when cultured on nutrient media containing heme or blood . In this case they show a positive reaction in the oxidase test. Another characteristic of lactococci is the need for complex growth factors and amino acids in cultivation. They can be cultivated on MRS agar , a nutrient medium that enables fastidious lactic acid bacteria to grow.

The temperature optimal for growth and reproduction are for most species in the range of 25–30 ° C, so Lactococcus is one of the mesophilic organisms. It also grows at 10 ° C, but not at 45 ° C, this is used as a criterion to distinguish it from the more thermophilic species of Streptococcus . Another distinguishing feature is that Lactococcus species show no hemolysis on an agar medium that contains blood - a so-called blood agar - whereas alpha or beta hemolysis can be observed with Streptococcus species. Lactococcus species survive heating at 60 ° C for 30 minutes and tolerate a high concentration of bile (mostly ox bile ) in the nutrient medium.

Lactic acid fermentation

Structural formula of the L- lactate ion
Structural formula of L- lactic acid

Lactococci can use various carbohydrates for energy production in one fermentation . A characteristic of fermentation ( fermentation ) is that the substrates are broken down without oxygen. The typical fermentation product for lactic acid bacteria is lactic acid or lactate (the anion of lactic acid), consequently this metabolic pathway is called lactic acid fermentation . A distinction is made between homofermentative and heterofermentative types. Homofermentative types produce almost exclusively lactic acid from glucose through fermentation, while heterofermentative types produce not only lactic acid, but also other end products to a significant extent, mostly ethanol and carbon dioxide , sometimes also acetic acid . The heterofermentatives usually lack the enzyme aldolase.

The representatives of the genus Lactococcus have the enzyme aldolase and all belong to the homofermentative species. Lactobacillus delbrueckii subsp. Also belongs to the homofermentative lactic acid bacteria . bulgaricus , the typical metabolic pathway is explained there. The enzyme lactate dehydrogenase present in Lactococcus species is also stereospecific , unlike in Lactobacillus delbrueckii subsp. bulgaricus almost exclusively produces L - (+) - lactate (syn .: ( S ) -lactate) in this reaction . The proportion of L - (+) - lactic acid is between 92 and 99%. This enantiomer is also known as dextrorotatory lactic acid .

In addition to glucose, other carbohydrates can also be used, including ribose , lactose (milk sugar), maltose and sucrose as well as the sugar alcohol mannitol . However, this does not apply to all species in the genus.

genetics

The genome of several bacterial strains from the genus Lactococcus has already been completely sequenced , this is especially true of the species Lactococcus lactis . The size of the genome of all representatives examined so far is between 2370 and 2810 kilobase pairs (kb), which is only 55% of the genome size of Escherichia coli . About 2300-2600 proteins are annotated . The small genome size is another indication of the adaptation to the milk habitat . There are many complex growth factors such as amino acids and vitamins , so that the bacterium has lost the ability to synthesize numerous metabolites over time .

Lactococcus is one of the gram-positive bacteria with a low GC content (the proportion of the nucleobases guanine and cytosine ) in the bacterial DNA . The GC content is between 38 and 41 mol percent, which is comparable to that of the related genera Streptococcus or Leuconostoc .

Pathogenicity

Lactococcus is not considered to be pathogenic ; most of the Lactococcus species are  assigned to risk group 1 by the Biological Agents Ordinance in conjunction with the TRBA ( Technical Rules for Biological Agents) 466 . Lactococcus garvieae is an exception and is assigned to risk group 2. However, there is the restriction that it was only detected as a pathogen in individual cases and this in people with weakened immune systems , and the identification of the species is often not reliable.

proof

A more general assessment of whether it is lactococci can be made using the light microscopic image after Gram staining . An oxidation-fermentation test (OF test) can be used to check whether they form both aerobic and anaerobic acid from glucose; no gas formation is observed. The catalase and oxidase test are negative, further biochemical tests to differentiate between the Lactococcus species contain typical detection reactions from a "colorful series" . It is checked which carbohydrates and other substrates they can utilize and which enzymes they have; the detection of arginine dihydrolase (ADH) is a distinguishing feature here . The growth in a nutrient medium with a proportion of 4% sodium chloride (NaCl) is also checked. The influence of different antibiotics is also examined to find out whether they are sensitive or resistant to them. To differentiate the Lactococcus species are u. a. the antibiotics cefuroxime , tetracycline , erythromycin and polymyxin B are used.

Occurrence

The types of Lactococcus are found primarily in milk and dairy products . They are used as starter cultures in the production of numerous dairy products, and because of the lactic acid they produce, they are also known as acid starters . They can also be found in or on plants and are involved in the production of silage . This can also be seen in the name of the species Lactococcus plantarum , planta from Latin means “plant”, plantarum means “of the plants” ( genitive , plural ).

Since the genus was established in 1986, species and subspecies have been added that occur in other habitats : In 2011, for example, the intestinal mucous membrane of trout and rainbow trout became Lactococcus lactis subsp. tructae isolated. As early as 1990, a new lactic acid bacterium was isolated from the Salmonidae ( salmon fish ) family and named Lactococcus piscium , piscis from Latin means “fish”, piscium means “the fish” (genitive, plural). Lactococcus lactis subsp. hordniae is named after the dwarf leafhopper Hordnia circellata , from which it was isolated, and Lactococcus chungangensis was found in 2008 in the foam of the activated sludge of a sewage treatment plant .

Lactococcus fujiensis is again of vegetable origin and was isolated from the outer leaves of Chinese cabbage in Japan in 2011 , while Lactococcus taiwanensis was found in Taiwan in 2013 , in one of the main ingredients for pobuzihi , a traditional fermented dish in Taiwan.

Systematics

External system

Lactococcus is closely related to the genus Streptococcus , both of which belong to the Streptococcaceae family . They used to be part of the genus Streptococcus - together with the enterococci, which are of fecal origin . In order to avoid the frequently pathogenic species from those which are harmless to humans, and e.g. In order to differentiate between species, some of which are also used in the food industry , a formal division was made into the genera Streptococcus , Enterococcus and Lactococcus . Enterococcus belongs to the Enterococcaceae family , which together with other families forms the order Lactobacillales, which are also known as lactic acid bacteria .

The separation of the genera Streptococcus and Lactococcus appears in part arbitrary. The investigations by Karl-Heinz Schleifer u. a. In 1985 chemotaxonomic traits were used. Some Streptococcus and Lactobacillus species were examined and their relationship was shown by the similarity of the composition of the bacterial cell wall , especially the teichonic acids anchored there . The lipids and fatty acids present and the menaquinones also show a similar pattern. This led to the assignment of the examined bacteria to the newly described genus Lactococcus . However, the old names are still used and are listed as a so-called basonym (comparable to the basionym in the taxonomy of plants), for example Streptococcus lactis is the basonym for Lactococcus lactis , as it was originally assigned to the genus Streptococcus .

Internal system

More than 200 strains belong to the genus Lactococcus , some of them are assigned to the species it contains, some of them are not yet clearly assigned. Currently (2013) 12 Lactococcus species and subspecies are listed by the Leibniz Institute DSMZ - German Collection of Microorganisms and Cell Cultures GmbH in the Prokaryotic Nomenclature up-to-date ("Prokaryotic nomenclature up-to-date "). This compilation includes all names validly published according to the Bacteriological Code and takes into account the validation list of the International Journal of Systematic and Evolutionary Microbiology . Lactococcus lactis is the type species .

  • Lactococcus chungangensis Cho et al. 2008, sp. nov.
  • Lactococcus fujiensis Cai et al. 2011, sp. nov.
  • Lactococcus garvieae ( Collins et al. 1984) Schleifer et al. 1986, comb. nov. (previously Streptococcus garvieae )
  • Lactococcus lactis (Lister 1873) Schleifer et al. 1986, comb. nov. (previously Streptococcus lactis )
    • Lactococcus lactis subsp. cremoris (Orla-Jensen 1919) Schleifer et al. 1986, comb. nov. (previously Streptococcus cremoris )
    • Lactococcus lactis subsp. hordniae ( Latorre-Guzmán et al. 1977) Schleifer et al. 1986, comb. nov. (previously Lactobacillus hordniae )
    • Lactococcus lactis subsp. lactis (Lister 1873) Schleifer et al. 1986, comb. nov. (previously Streptococcus lactis )
    • Lactococcus lactis subsp. tructae Pérez et al. 2011, subsp. nov.
  • Lactococcus piscium Williams et al. 1990, sp. nov.
  • Lactococcus plantarum ( Collins et al. 1984) Schleifer et al. 1986, comb. nov. (previously Streptococcus plantarum )
  • Lactococcus raffinolactis (Orla-Jensen and Hansen 1932) Schleifer et al. 1988, comb. nov. (previously Streptococcus cremoris )
  • Lactococcus taiwanensis Chen et al. 2013, sp. nov.

The bacterial strains formerly known as Streptococcus lactis subsp. diacetilactis (also known as Streptococcus diacetilactis or Streptococcus diacetylactis ) as well as the bacterial strains that were previously assigned to Lactobacillus xylosus now belong to the subspecies Lactococcus lactis subsp. lactis . The assignment of Lactococcus garvieae has not yet been fully clarified. It does not seem to match the other lactococci entirely, partly because it can cause disease. In 1996, strains of water buffalo belonging to the species were isolated which had developed mastitis without showing symptoms. However, after genotypic and phenotypic examinations, they were identified as belonging to the species Enterococcus seriolicida Kusuda et al. 1991 assigned.

In the taxonomic assignment of new bacterial strains, genetic studies are increasingly being carried out; the DNA sequences in the genome are examined by means of DNA-DNA hybridization and, in the case of bacteria, also the 16S rRNA, a typical representative of ribosomal RNA for prokaryotes . The analysis of the 16S rRNA sequences in Lactococcus taiwanensis shows an agreement of 98.22-98.82% to the Lactococcus lactis subspecies, the comparison of the DNA sequences shows an agreement of 9.7-15.2%, these deviations lead to the fact that it is called its own species. In the case of Lactococcus fujiensis , the 16S rRNA sequences correspond to 94.4% with Lactococcus lactis and Lactococcus garvieae , while the comparison of the DNA sequences shows an agreement of less than 20.2% with the type strains of other Lactococcus species.

etymology

The generic name refers to the occurrence and appearance of the cells, lactis from Latin stands for “milk” and κόκκος kokkos is ancient Greek for “berry”, Lactococcus is consequently a coke-shaped bacterium in milk.

Industrial importance

A piece of butter that Lactococcus is involved in making.

Lactic acid fermentation is mainly used in the food industry in the manufacture of dairy products such as cheese and yoghurt . Without lactic acid bacteria there would be practically no dairy products. In the dairy , pure cultures of Lactococcus species are used in the production of sour milk , sour cream products such as crème fraîche , sour cream butter , buttermilk , quark and other fresh cheese products by adding them as starter cultures . Sour milk and sour cream contain 0.5–0.9% lactic acid due to the lactic acid fermentation carried out by Lactococcus . In sour cream butter, the formation of diacetyl by the Lactococcus species is also important. Diacetyl is desirable as a flavoring substance with a typical smell and taste of butter.

In the cheese production are Lactococcus TYPES as so-called mesophilic lactic starter used and then the milk at 20-30 ° C incubation . For Coagulation an addition of can Lab done. In addition to the Lactococcus species, other lactic acid bacteria are usually also involved.

swell

literature

  • Michael Teuber, Arnold Gleis: The Genus Lactococcus. In: The Prokaryotes, A Handbook of the Biology of Bacteria . Volume 4. Bacteria: Firmicutes, Cyanobacteria. Edited by Martin Dworkin, Stanley Falkow, Eugene Rosenberg, Karl-Heinz Schleifer, Erko Stackebrandt. 3. Edition. Springer, New York 2006. ISBN 978-0-387-25494-4
  • Milk and dairy products . In: Herbert Weber (Hrsg.): Microbiology of food . 2nd Edition. tape 2 . Behr's Verlag, Hamburg 2006, ISBN 978-3-89947-251-6 .

Individual evidence

  1. ↑ a b c d e f Michael T. Madigan, John M. Martinko, Jack Parker: Brock Mikrobiologie. German translation edited by Werner Goebel. 1st edition. Spektrum Akademischer Verlag GmbH, Heidelberg / Berlin 2000, ISBN 3-8274-0566-1 , pp. 558-563.
  2. ↑ a b c d e Gunther Müller: Fundamentals of food microbiology . 6th edition. Steinkopff Verlag, Darmstadt 1986, ISBN 3-7985-0673-6 , p. 55, 178 .
  3. ↑ a b c d e f g Hans G. Schlegel, Christiane Zaborosch: General microbiology . 7th edition. Thieme Verlag, Stuttgart / New York 1992, ISBN 3-13-444607-3 , p. 100, 296-304 .
  4. ↑ a b c d T. Pérez, JL Balcázar u. a .: Lactococcus lactis subsp. tructae subsp. nov. isolated from the intestinal mucus of brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss). In: International journal of systematic and evolutionary microbiology. Volume 61, No. 8, August 2011, pp. 1894-1898, ISSN  1466-5034 . doi : 10.1099 / ijs.0.023945-0 . PMID 20833888 .
  5. ^ A b c Hans-Dieter Belitz , Walter Grosch: Textbook of food chemistry . 4th edition. Springer Verlag, Heidelberg / Berlin 1992, ISBN 3-540-55449-1 , p. 471-476 .
  6. ↑ a b Lactococcus lactis. In: National Center for Biotechnology Information (NCBI) Genome website . Retrieved November 30, 2013 .
  7. ↑ a b TRBA (Technical Rules for Biological Agents) 466: Classification of prokaryotes (bacteria and archaea) into risk groups. In: Website of the Federal Institute for Occupational Safety and Health (BAuA) . April 25, 2012. Retrieved November 17, 2013 .
  8. ↑ a b c Der Kleine Stowasser, Latin-German school dictionary, edited by Dr. Michael Petschenig . B. Freytag Verlag, Munich 1971, ISBN 3-486-13402-7 .
  9. ↑ AM Williams, JL Fryer, MD Collins: Lactococcus piscium sp. nov. a new Lactococcus species from salmonid fish. In: FEMS microbiology letters. Vol 56, Numbers 1-2, March 1990, pp 109-113, ISSN  0378-1097 . PMID 1692000 .
  10. ↑ a b KH Schleifer, J. Kraus u. a .: Transfer of Streptococcus lactis and related Streptococci to the genus Lactococcus gen. nov. In: Systematic and applied microbiology. Volume 6, No. 2, September 1985, pp. 183-195, ISSN  0723-2020 . doi : 10.1016 / S0723-2020 (85) 80052-7 .
  11. ↑ SL Cho, SW Nam et al. a .: Lactococcus chungangensis sp. nov., a lactic acid bacterium isolated from activated sludge foam. In: International journal of systematic and evolutionary microbiology. Volume 58, No. 8, August 2008, pp. 1844-1849, ISSN  1466-5026 . doi : 10.1099 / ijs.0.65527-0 . PMID 18676466 .
  12. ↑ a b Y. Cai, J. Yang, H. Pang, M. Kitahara: Lactococcus fujiensis sp. nov., a lactic acid bacterium isolated from vegetable matter. In: International journal of systematic and evolutionary microbiology. Volume 61, No. 7, July 2011, pp. 1590-1594, ISSN  1466-5034 . doi : 10.1099 / ijs.0.025130-0 . PMID 20675438 .
  13. ↑ a b YS Chen, CH Chang u. a .: Lactococcus taiwanensis sp. nov., a lactic acid bacterium isolated from fresh cummingcordia. In: International journal of systematic and evolutionary microbiology. Volume 63, No. 7, July 2013, pp. 2405-2409, ISSN  1466-5034 . doi : 10.1099 / ijs.0.045757-0 . PMID 23178728 .
  14. ↑ JP Euzéby, Aidan C. Part: Order Lactobacillales. In: List of Prokaryotic names with Standing in Nomenclature (LPSN) . Retrieved November 29, 2013 .
  15. ↑ VBD Skerman, Vicki McGowan, PHA Sneath (Eds.): Approved Lists of Bacterial Names (Amended) . 2nd Edition. ASM Press, Washington (DC), USA 1989, ISBN 978-1-55581-014-6 .
  16. ↑ a b c d J. P. Euzéby, Aidan C. Parte: Genus Lactococcus. (No longer available online.) In: List of Prokaryotic names with Standing in Nomenclature (LPSN) . Archived from the original on November 4, 2013 ; Retrieved November 29, 2013 . 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.  @1@ 2Template: Webachiv / IABot / www.bacterio.net
  17. ↑ Taxonomy Browser Lactococcus. In: National Center for Biotechnology Information (NCBI) website . Retrieved November 30, 2013 .
  18. ^ Prokaryotic Nomenclature Up-to-date. In: Website of the Leibniz Institute DSMZ - German Collection of Microorganisms and Cell Cultures GmbH . Retrieved November 30, 2013 .
  19. ↑ LM Teixeira, VL Merquior a. a .: Phenotypic and genotypic characterization of atypical Lactococcus garvieae strains isolated from water buffalos with subclinical mastitis and confirmation of L. garvieae as a senior subjective synonym of Enterococcus seriolicida. In: International journal of systematic bacteriology. Volume 46, No. 3, July 1996, pp. 664-668, ISSN  0020-7713 . PMID 8782673 .

Web links

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