Lactococci are well-known by important significance in basic microbiology, genetics, molecular biology, as well as in food science and biotechnology. Lactococcus lactis, is currently very important for industrial fermentations, especially dairy products. In 1873, the scientist Joseph Lister began experiments with boiled milk as a nutrient medium and by luck he obtained the first pure culture of this bacterium. He was driven to perform these experiments, because of his interest in proving Pasteur’s germ theory of fermentative changes did exist. In 1909, because of so many reinvestigations, this bacterium was later renamed Streptococcus lactis. And only until recently it was renamed and clearly separated from the genera of streptococci.
Lactococci are generally known to be safe for human consumption, and they have never been identified as causes of infectious disease. Because of this fact, this bacterium is used in large quantities in the dairy industries in the production of many different products.
Members of the Lactococcus genus are gram-positive, round-shaped cells. Depending on their growth conditions they typically appear to be 0.5-1.5µm in size. A characteristic of the Lactococcus lactis that make them different then and members of the Streptococcus genus, is that these species grown in pairs or in short chains, unlike the long chains that the Streptococcus species form. In order to be able to grown inside of milk L. lactis relies on the degradation of milk protein into peptides. Basically how this works is that when it is added to the milk, this bacterium uses enzymes to produce energy molecules (ATP) from lactose. The byproduct of ATP is lactic Acid. Once lactic acid is produced it curdles the milk to form curds, which are used to produce cheese (also produces whey.
Being in Missouri and surrounded by many dairy farmers, I thought this specific prokaryote would be an interesting species to study and present to the class. The whole finding of L. lactis was so important to the study and work in fermentation and the ripening of milk, cream and cheese, it played a major role in the development of where milk and dairy products have become today.
References:
http://distans.livstek.lth.se:2080/L_coccus.htm
http://www.genoscope.cns.fr/externe/English/Projets/Projet_AI/AI.html
http://www.mywiseowl.com/articles/Lactococcus_lactis
Balows, Albert; Harder, Wim; Schleifer, Karl-Heinz. The Prokaryotes. New York: Springer-Verlag New York Inc. 1981.
*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.
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