A Microbial Biorealm page on the genus Lactococcus lactis
Description and significance
Lactococcus lactis is a rod shaped, gram positive bacteria used widely for producing fermented dairy products like milk, cheese, and yogurt. It is believed that in nature, L. lactis stays dormant on plant surface awaiting to be ingested along with the plant into animal gastrointestinal tract, where it becomes active. It is classified as a lactic acid bacterium(LAB) which converts carbohydrates into lactic acid. It plays an significant role to the food industry, so studies have been done on the genome of Lactococcus lactis extensively to improve its application in dairy products. Not only it is important in dairy production, it has potential of use as oral vaccine and foreign protein production and metabolite.
The genome of L. lactis is a circular chromosome with 2,365,589 base pairs where 86% of the genome codes for protein, 1.4% for RNA, and 12.6% for noncoding region. The initiation genes for DNA replication in L. lactis includes dnaB, dnaD, and dnaI, and polC and dnaE for DNA polymerase III. There are around some 30 genes found in L. lactis for transcription along with only 3 sigma-factor, while the translation mechanism comprise of 119 genes.
Cell structure and metabolism
The main metabolic pathway of L. lactis is the production of lactic acid that is used in food production. L. lactis utilizes anaerobic glycolysis to break down small amount of fermented sugar to pyruvate, then convert pyruvate to lactic acid with the main enzyme ldh, lactate dehydrogenase. Lactate will cause protons to be pumped out creating the membrane potential necessary for energy production. With this mechanism, L. lactis does not contain the genome encoded for citric cycle and gluconeogenesis, but does have functioning genome for aerobic respiration. Formation of lactate is not the only one fermentative pathway of L. lactis, so food industry has studied further on many other fermentative products. The amount of each produced mainly bases on its corresponding enzymes activities on pyruvate. The understanding of each of the fermentative pathways helps food industry to synthesize compounds that are desired by manipulating and controlling the bacteria.
Describe any interactions with other organisms (included eukaryotes), contributions to the environment, effect on environment, etc.
Lactococcus lactis is a nonpathogenic bacteria. There is no evidence that L. lactis can be harmful to human or animal.
Application to Biotechnology
Does this organism produce any useful compounds or enzymes? What are they and how are they used?
1. In poor country where vaccine is limited and not affordable, disease could be spread easily. A research study attempts to prove that a mucosal vaccine against Streptococcus pneumoniae using lactococcu lactis is more effective than vaccination with purified live antigen. The result shows that L. lactis has more potential and safety in developing vaccine in human and should be considered to be used against other pathogens.
[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.
Edited by student of Rachel Larsen and Kit Pogliano