Lactobacillus sakei
A Microbial Biorealm page on the genus Lactobacillus sakei
Classification
Higher order taxa
Bacteria; Firmicutes; Lactobacillales; Lactobacillaceae; Lactobacillus
Genus
Genus: Lactobacillus; Species: sakei
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NCBI: Taxonomy |
Description and significance
Lactobacillus sakei is a Gram-positive anaerobic bacterium commonly found living on fresh meat and fish. This bacterium is valuable in the fermentation of meat products as well as exhibits properties that allow for better preservation and storage of fresh meats and fish (5). It is the predominant bacteria used for meat fermentation in Europe, whereas Pediococcus pentosaceus tends to be widely used in the United States (5). Lactobacillus sakei took its name from rice alcohol, or sake, which was the product that it was first described in (5).
Sequencing Lactobacillus sakei’s genome was important in determining how this bacterium is so well adapted to meat. A team of INRA (Institut National de La Recherche Agronomique) researchers was able to determine its genome and found that its effectiveness in fermentation and food storage is indicative of its ability to sustain life even under challenging environmental conditions, its ability to produce toxics to kill other bacteria, and its capability to use nutrients in meat for self growth (5).
Genome structure
The entire genome of Lactobacillus sakei strain 23K was determined to be a circular chromosome containing 1,884,661 base pairs. “The genome consisted of 1,883 protein genes, seven rRNA gene clusters, and had a G + C content of 41.25% that appears to be uneven along the chromosome (1).”
Cell structure and metabolism
Although raw meat provides Lactobacillus sakei nutrients for growth, it contains limited amounts of carbohydrates. Out of the few sugars found in meat and raw fish, Lactobacillus sakei can utilize only glucose and ribose (7). It is no surprise that upon examination of its genome, very small transport systems are present for sugar uptake (1). Because sugars are rapidly exhausted in meat, Lactobacillus sakei is also able to catabolize nucleosides such as inosine and adenosine for energy source (1).
Ecology
Lactobacillus sakei interacts with other bacteria present on meat products. Among them are the pathogenic bacteria such as Escherichia coli and Listeria monocytogenes which are very dangerous to humans (5). Other bacteria include food-spoiling bacteria like Psuedomonas fragi and Brochothrix thermosphacta that do not necessarily pose danger to health, however, could damage meat products (5). Lactobacillus sakei has the ability to produce ribosomally-synthesized antimicrobial peptides called bacteriocins that inhibit growth of some of these bacteria (6). For instance, it was found in a research study that the bacteriocin-positive strain of Lactobacillus sakei was able obstruct the growth of Listeria monocytogenes in rainbow trout fillets in specific environmental conditions, whereas bacteriocin-negative strain of Lactobacillus sakei provided no inhibition (4).
Application to Biotechnology
Lactobacillus sakei is able to produce bacteriocin called sakacin P that inhibits growth of several pathogenic and food-spoiling bacteria present in meat and fish products. It is no wonder that Lactobacillus sakei is bacteria widely used for meat fermentation.
Current Research
Several research studies have been performed on Lactobacillus sakei to further determine optimal environmental conditions, as well as its capacity to ferment meat.
Lactobacillus sakei is able to grow under both anaerobic and aerobic conditions. With this characteristic, a research study was performed to determine the proteins and genes involved when Lactobacillus sakei is growing anerobically. Using two-dimensional electrophoresis, they found that the protein that is over-expressed during anaerobic growth was a peptidase and its corresponding gene is pepR. After performing several experiments on this gene, they found that pepR was indeed responsible for the Lactobacillus sakei’s ability to live under anaerobic environment (2).
In another study, it was found that four genes of Lactobacillus sakei namely ctsR, asnA2, LSA1065, and LSA1194 were involved during fermentation of raw sausage. “Inactivation of the heat shock regulator gene ctsR resulted in increased growth, whereas knockout of the genes asnA2, LSA1065, and LSA1194 resulted in attenuated performance compared to the wild-type strain (3).”
References
Edited by student of Rachel Larsen and Kit Pogliano
