Lactococcus lactis

Chances are that almost anyone who reads this post has eaten Lactococcus lactis. And they almost certainly did it willingly. What, you may ask, would possess someone to willingly eat bacteria? Cheese. Lactococcus lactis is involved in the production of cheese. When inoculated into milk it ferments lactose to produce lactic acid.[1] The lactic acid curdles the milk, eventually producing cheese. Lactococcus lactis is involved in the production of Brie, Camembert, Cheddar, Colby, Gruyère, Monterey Jack, Parmesan, Roquefort, and many other cheeses, as well as buttermilk and sour cream.[2] There are two subspecies: lactis and cremoris. Lactobacillus lactis subsp. lactis is used for making soft cheeses while Lactobacillus lactis subsp. cremoris is used for making hard cheeses.[3] All this has led to it being named the state microbe of Wisconsin.[4]

However, making cheese and buttermilk isn't Lactococcus lactis' only claim to fame. It is the first genetically engineered bacterium to be used in the treatment of human disease (Crohn's disease).[5] It is also being considered as a vehicle for delivering a vaccine against Streptococcus pneumoniae (the major cause of bacterial pneumonia).[6] It is closely related to several important probiotic bacteria, including Lactobacillus acidophilus, Lactobacillus rhamnosus, and Lactobacillus reuteri. Lactococcus lactis is also known to produce nicin, an antimicrobial compound that is used as a food preservative against harmful bacteria such as Listeria, Clostridium, and Staphylococcus.[7]

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Notes:

 

[1] Lactose is a disaccharide, which means it's made up of two sugars stuck together. In the case of lactose, it consists of one glucose and one galactose (see image above, left). Lactic acid (the end product of fermentation by Lactococcus lactis) is seen on the right.

[2] See http://en.wikipedia.org/wiki/Lactococcus lactis#Cheese production. The buttermilk and sour cream also require inoculation with Leuconostoc mesenteroides.

[3] See http://microbewiki.kenyon.edu/index.php/Lactococcus lactis#Description and significance.

[4] See http://www.nytimes.com/2010/04/16/us/16microbe.html.

[5] See http://en.wikipedia.org/wiki/Lactococcus lactis.

[6] Medina, M., et al. (2010) "Lactococcus lactis as an adjuvant and delivery vehicle of antigens against pneumococcal respiratory infections." Bioeng Bugs, 1 (5): 313–325. doi:  10.4161/bbug.1.5.12086.

[7] See http://textbookofbacteriology.net/featured microbe.html.

Image attributions:

Microscopic image of Gram-stained Lactococcus lactis is by Minyoung Choi, available at http://en.wikipedia.org/wiki/File:Lactococcus lactis.jpg.

Chemical structure of lactose is by Yikrazuul, available at http://en.wikipedia.org/wiki/File:Beta-D-Lactose.svg.

Chemical structure of lactic acid is by NEUROtiker, available at http://en.wikipedia.org/wiki/File:Lactic-acid-skeletal.svg.