Browsing by Author "Van Reenen, C. A."

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    Optimized production of bacteriocin ST11BR, generated by Lactobacillus paracasei subsp. paracasei ST11BR isolated from traditional South African beer
    (Academy of Science for South Africa, 2005) Todorov, S. D.; Van Reenen, C. A.; Dicks, L. M. T.
    Little is known about the production of antimicrobial peptides (bacteriocins) by lactic acid bacteria in traditional South African beer and their inhibition of food spoilage or pathogenic bacteria. In this paper, we report on bacteriocin ST11BR, produced by Lactobacillus paracasei subsp. paracasei ST11BR isolated from beer made with maize, barley, soy flour and sugar (sucrose). Bacteriocin ST11BR is a 3.2-kDa peptide with activity against Lactobacillus casei, L. sakei, Pseudomonas aeruginosa and Escherichia coli. The peptide is sensitive to proteinase K and pronase, but not to α-amylase. Glycerol in the growth medium repressed bacteriocin production. Tween 80 suppressed production by more than 50%, irrespective of the initial pH of the medium. MRS broth adjusted to pH 4.50 yielded 3200 AU/ml bacteriocin. The corresponding value at pH 5.0, 5.5, 6.0 and 6.5 was 12 800 AU/ml. The highest yield (25 600 AU/ml) was recorded in MRS broth without Tween 80, and with meat extract as the only nitrogen source, or a combination of meat extract and tryptone, or yeast extract and tryptone. Growth in the presence of tryptone as sole nitrogen source achieved only 12 800 AU/ml bacteriocin. Yeast extract, or a combination of yeast extract and meat extract, yielded 6400 AU/ml. A growth medium comprising 20.0 g/l maltose, sucrose or mannose yielded bacteriocin levels of 25 600 AU/ml, whereas the corresponding values for the same concentration of glucose or fructose were 12 800 AU/ml and 1 600 AU/ml, respectively. Lactose did not stimulate bacteriocin production - the highest yield (6 400 AU/ml) was generated in the presence of 10.0 g/l. No difference in bacteriocin activity was recorded when strain ST11BR was grown in the presence of 2.0 g/l KH2PO4 and 2.0-10.0 g/l K2HPO 4. However, cyanocobalamin, thiamine and DL-6,8-thioctic acid (1.0 ppm), but not L-ascorbic acid, stimulated peptide production. This study provided valuable information on the optimal production of bacteriocin by a strain of L. paracasei naturally present in a traditional beer.
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    Strains of lactobacillus plantarum in grape must are also present in the intestinal tract of vinegar flies
    (South African Society for Enology and Viticulture, 2006) Groenewald, W. H.; Van Reenen, C. A.; Dicks, L. M. T.
    Twenty-one lactic acid bacteria isolated from the intestinal tract of Drosophila simulans Stuvervant and nine from Merlot noir grapes were identified as L. plantarum by PCR with species-specific primers and 16S rDNA sequencing. The 30 isolates grouped into four clusters based on RAPD-PCR banding patterns, suggesting that they belong to at least four genotypic groups. Thirteen isolates from grape must and five from the flies yielded identical RAPDPCR banding patterns and grouped into one cluster, suggesting that they are descendants from the same strain. Concluded from these results, L. plantarum (or at least descendants from a specific strain) has the ability to use vinegar flies as a host and vector to infect grape must. Further research is needed to determine the role of this specific strain in wine fermentations.