Sakacin P is a heat-stable, unmodified peptide bacteriocin produced by Lactobacillus sake LTH 673. The strain was isolated from fermented dry sausages and is well adapted to this habitat. The bacteriocin inhibits the growth of the opportunistic food pathogens Enterococcus faecalis and Listeria monocytogenes and therefore, it may improve the hygienic status of fermented food, i.e. meat products. Oligonucleotide probes were designed from the N-terminal amino acid sequence of sakacin P and used to identify sakP, the structural gene of sakacin P, on the chromosome of L. sake LTH 673. SakP was cloned into Escherichia coli NM554 and the nucleotide sequence of the gene and its adjacent regions were determined. Sakacin P appears to be synthesized as a prepeptide of 61 amino acids which is proteolytically processed to the mature bacteriocin consisting of 43 amino acids. Sequencing of the cloned fragment also revealed the presence of two other open reading frames orfX and orfY, which are located upstream and downstream of sakP, respectively, putatively encoding proteins of 52 and 98 amino acids, respectively. The functions of both ORFs remain unknown. Primer extension analysis revealed a promoter upstream of sakP. T w o transcripts of approximately 035 and 1.0 kb were detected by Northern hybridization encoding either only sakP, or both sakP and o m , respectively.
Curvacin A is a bacteriocin produced by Lactobacillus curvatus LTH1174 which is a potential starter organism for the production of fermented dry sausages. This peptide inhibits the growth of the opportunistic food pathogens Listeria monocytogenes and Enterococcus faecalis and thus, curvacin A may enable better performance of a starter and improvement of the hygienic status of meat products. Oligonucleotides were constructed deduced from the peptide sequence and used for the identification of the curvacin A structural gene curA on a 60 kb plasmid of L. curvatus LTH1174. Plasmid-cured derivatives of this strain were unable to produce curvacin A but were still resistant to the bacteriocin. CurA was cloned into Escherichia coli NM554 and its nucleotide sequence was determined. Sequencing revealed the presence of an additional open reading frame of 51 amino acids with unknown function. A promoter was detected upstream of curA by primer extension. Both reading frames form a single transcript. Curvacin A is synthesised as a prepeptide of 59 amino acids which is proteolytically processed to the mature bacteriocin of 41 amino acids.
By tradition lactic acid bacteria (LAB) are involved in the production of fermented foods. These constitute one quarter of our diet and are characterized by a safe history, certain beneficial health effects, and an extended shelf life when compared with raw materials. The various fermenting substrates are habitats for specific LAB that differ in their metabolic potential. The health effects exerted by LAB are the following: 1. Production of lactic acid and minor amounts of acetic and formic acid. These cause: a drop in pH and thereby growth inhibition of food spoiling or poisoning bacteria; killing of certain pathogens; detoxification by degradation of noxious compounds of plant origin (usually in combination with plant-derived enzymatic activities). 2. Production of antimicrobial compounds (e.g. bacteriocins, H2O2, fatty acids). 3. Probiotic effects as live organisms in food. The wholesomeness of LAB can also be extended to fields outside human nutrition, as they may act as probiotics in animal production or as plant protectives in agriculture and thus contribute to healthy raw materials for food production. Modern concepts or perspectives of the application of LAB include the following: 1. Selection of the best adapted and safely performing LAB strains. 2. Selection of strains with probiotic effects. 3. Selection of strains with health-promoting effects (e.g. production of vitamins or essential amino acids, anti-tumour activity). 4. Selection of strains with food protective activities (inhibiting spoilage or food pathogens). These strains can be added to food or used as starters in food fermentations. They may be found as wild-type organisms or can be obtained by genetic engineering.(ABSTRACT TRUNCATED AT 250 WORDS)
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