The growth performance of six L. sakei strains was studied of salt content and temperature. Afterward, the strains were inoculated in a defined medium containing 20 free amino acids or glucose to understand their metabolism in general. The growth performance of the six strains was then measured after 24 h of incubation in D.M. The resulting cell number, pH, and amino acid contents were also quantified.
Genetic variability of L. sakei
Lactobacillus sakei is one of the most common probiotic bacteria used in the food industry and has a wide range of probiotic functions, including improving metabolic syndrome and immunity, alleviating the inflammatory response in colitis mice, and reducing the occurrence of atopic dermatitis. Despite these benefits, relatively few studies have examined the genetic variability of this species. In this study, the genetic diversity of 68 strains of L. sakei was assessed using 14 laboratory-isolated strains and 54 with available genetic information at NCBI.
The genome sequence of L. sakei revealed that its genetic variability was largely due to various strains that possessed different enzymes for carbohydrate utilization. These enzymes, which belong to four families, were analyzed by thermographic analysis and showed that the genes from different strains were active in several metabolic pathways. These findings have important implications for the biopreservation of meat products and the development of novel pharmaceuticals.
The genome of L. sakei also revealed two putative cytochromes with unknown functions. One of these was a monooxygenase (MD-P-P), with the 23K strain being transcriptionally disrupted. Other putative oxidoreductases included heme-dependent catalase and iron-containing Dye-type peroxidase.
A study by Amor et al., 2005, highlighted phenotypic differences among 36 L. sakei strains, including the growth performance at different pH levels. The authors also compared NaCl levels, final pH, and temperature. The researchers found that some strains performed better at 10% of NaCl concentrations. The authors suggest that this may contribute to the genetic variability of L. sakei strains.
The researchers found 117 genes associated with antibiotic resistance in 14 L. sakei strains. These strains all had high tolerance levels for aminoglycosides and glycopeptides. They also had a high tolerance to streptogramin, kanamycin, and vancomycin. Further analysis is needed to determine the origin of these strains, as they are found in different fermented products.
Bacteriocin production by L. sakei
Bacteriocin A is a bacterial protein produced by Lactobacillus sakei. It is a bactericidal peptide with a specific inhibitory spectral pattern. ItA limited set of LAB strains produces EntA. The bacteriocin is produced in two different stages. First, the bacterial cell is inoculated with the bacteriocin-producing enzyme, and second, the bacteria are inoculated with the bacteria’s active peptide. Both EntA and bacteriocin-producing pSIP-vectors are used to express the bacteriocin.
Bacteriocin production is tightly regulated by the environment in which the bacteria live. The production of bacteriocin depends on the accumulation of an inducing peptide and a critical cell density. This peptide can be switched on or off by an increasing or decreasing cell density. Bacteriocin is commonly produced by Lactobacillus sakei in the fermentation process.
The level of bacteriocin production in CTC 494 cells is influenced by nutrient availability. Bacteriocin production per cell is affected by the availability of nutrients, including salt. Bacteriocin production per cell reaches a plateau due to the accumulation of lactic acid. The increase in biomass does not lead to an increase in bacteriocin production per cell.
In the United States, it is also used in the fermentation process of meat. It has applications in a wide range of food industries because of its ability to survive under both aerobic and anaerobic conditions. In addition to fermenting meat, Lactobacillus sakei is used in factory processing. It can cause slimy textures in processed meat. Its growth is regulated by the levels of a gene called pep.
The antibacterial agar diffusion bioassay studied the antibiotic activity of eight selected LAB isolates. The LAB isolates were tested against six common food pathogens and a spoilage organism. Indicator organisms included L. innocua and Erw. carotovora, and Ps. fluorescens. The inhibitory activity of the isolates was maintained at the same temperature after acidification.
Redox metabolism in L. sakei
Redox metabolism in Lactobacillus sakei has many functions. This common Gram-positive bacterium can produce a wide range of compounds, including inosine and ribose. Interestingly, this bacterium also synthesizes pyrimidines and purines de novo. It also contains genes that catabolize inosine and adenosine. Although it is unlikely to affect human health directly, the metabolism of these substances could improve their ability to thrive on meat.
The bacterium’s genome has revealed two putative cytochromes with unknown functions. One of these proteins is an iron-containing Dye-type peroxidase, and the other is a thiol peroxidase. The latter is thought to play a role in the antibacterial effect of the bacterium on the food it consumes. Moreover, some researchers have suggested that Lactobacillus sakei also possesses a gene for OhrA, which may act as a compensating enzyme.
These findings suggest that the redox-related pathways of L. sakei may have evolved from a meat-growing environment. Their physiological functions are essential for the transit and colonization of the gastrointestinal tract (GIT).
Redox metabolism in Lactobacillus sakei is important for its resistance to oxidative stress. Understanding how this bacterium responds to oxidative stress could lead to new bio preservative strategies that preserve fresh meat without compromising safety. Moreover, determining how it acquires iron/heme can help us understand the relationship between pathogenic and harmless bacteria within the food matrix.
The evolutionary history of L. sakei has revealed that it has distinct ecotypes linked to different environmental reservoirs. The MLST scheme may provide a convenient tool for analyzing the population dynamics of strains in food products. Further research could help identify the best antibiotics to use for fermentation and prevent foodborne illnesses. It can also help develop effective bioprospecting protocols. The study also points to the role of genetic diversity in microbial communities.
Redox metabolism in Lactobacillus sakei has been studied since the 1990s. Currently, we know about four carbohydrate-active enzyme families. The highest-level enzyme is the G.H. family, followed by the G.T. family. The other two families are the GH13-29 family, related to starch and trehalose metabolism. However, the GH2 and GT4 enzymes are associated with atypical cell shape and surface structure.
Growth performance of six L. sakei strains in D.M.
We evaluated the growth performance of six lactobacillus sakeI strains in D.M. These bacteria are used as starter cultures for industrial meat fermentations and are known to inhibit the growth of pathogenic and spoilage microorganisms. Their genome contains approximately 500 genes that regulate cell surface, redox regulation, carbon metabolism, and bacteriocin production. Interestingly, these bacteria were also able to tolerate redox variation.
We first determined the carbon source used for growth. Using ribose as the carbon source, we found that the growth performance of the L. sakei strain 23K was significantly enhanced on ribose. Montanari et al. also found a similar effect of ribose on arginine deiminase (ADI) transcription in Lat. sakei strains grown on ribose, glucose, and acetate.
The remaining strains did not significantly differ in growth performance. After 48 hours, cell viability was decreased. Strains DSMZ 20017t and Chr82 had the lowest cell viability, and other strains showed relevant reductions. These results suggest that the metabolomic profiles of L. sakei strains differ under different nutritional conditions. We recommend adjusting the pH and nutritional conditions of the D.M. to optimize growth performance.
The results suggest that the bacterial communities of different Lactobacillus strains vary in intraspecies diversity. Three of the strains used in this study were obtained from the University of Bologna’s collection. The authors identified ten strain clusters and showed that the bacterial communities of these six isolates are related to each other. In addition, iron and heme in the meat also enhance the growth of the L.A. sakei strain LS25.
Several strains of L. sakei have a different evolutionary history. The current population comprises isolates from three ancestral lineages, with each showing a distinct evolutionary history. In addition, the MLST scheme is an easy-to-use tool for analyzing population dynamics. Using the MLST scheme, we can compare the growth performance of six strains in D.M. and determine which one is most compatible with particular environments.