Vesa Joutsjoki

Expression of six peptidases from Lactobacillus helveticus in Lactococcus lactis.

ABSTRACT For development of novel starter strains with improved proteolytic properties, the ability of Lactococcus lactis to produceLactobacillus helveticus aminopeptidase N (PepN), aminopeptidase C (PepC), X-prolyl dipeptidyl aminopeptidase (PepX), proline iminopeptidase (PepI), prolinase (PepR), and dipeptidase (PepD) was studied by introducing the genes encoding these enzymes intoL. lactis MG1363 and its derivatives. According to Northern analyses and enzyme activity measurements, the L. helveticus aminopeptidase genes pepN, pepC, andpepX are expressed under the control of their own promoters in L. lactis. The highest expression level, using a low-copy-number vector, was obtained with the L. helveticus pepN gene, which resulted in a 25-fold increase in PepN activity compared to that of wild-type L. lactis. The L. helveticus pepI gene, residing as a third gene in an operon in its host, was expressed in L. lactis under the control of the L. helveticus pepX promoter. The genetic background of the L. lactis derivatives tested did not affect the expression level of any of the L. helveticus peptidases studied. However, the growth medium used affected both the recombinant peptidase profiles in transformant strains and the resident peptidase activities. The levels of expression of the L. helveticus pepD and pepR clones under the control of their own promoters were below the detection limit in L. lactis. However, substantial amounts of recombinant pepD and PepR activities were obtained in L. lactis when pepDand pepR were expressed under the control of the inducible lactococcal nisA promoter at an optimized nisin concentration.

In vitro growth inhibition of Helicobacter pylori by lactobacilli belonging to the Lactobacillus plantarum group.

Aims:  The aim of this study was to test and locate the in vitro anti‐Helicobacter activity of seven Lactobacillus strains belonging to Lactobacillus plantarum group.

Potential of lactic acid bacteria in aflatoxin risk mitigation

Aflatoxins (AF) are ubiquitous mycotoxins contaminating food and feed. Consumption of contaminated food and feed can cause a severe health risk to humans and animals. A novel biological method could reduce the health risks of aflatoxins through inhibiting mold growth and binding aflatoxins. Lactic acid bacteria (LAB) are commonly used in fermented food production. LAB are known to inhibit mold growth and, to some extent, to bind aflatoxins in different matrices. Reduced mold growth and aflatoxin production may be caused by competition for nutrients between bacterial cells and fungi. Most likely, binding of aflatoxins depends on environmental conditions and is strain-specific. Killed bacteria cells possess consistently better binding abilities for aflatoxin B1 (AFB1) than viable cells. Lactobacilli especially are relatively well studied and provide noticeable possibilities in binding of aflatoxin B1 and M1 in food. It seems that binding is reversible and that bound aflatoxins are released later on (Haskard et al., 2001; Peltonen et al., 2001). This literature review suggests that novel biological methods, such as lactic acid bacteria, show potential in mitigating toxic effects of aflatoxins in food and feed.

Comparative Study of Sugar Fermentation and Protein Expression Patterns of Two Lactobacillus plantarum Strains Grown in Three Different Media

ABSTRACT A comparative study of two strains of Lactobacillus plantarum (REB1 and MLBPL1) grown in commercial medium (MRS broth), cucumber juice, and liquid pig feed was performed to explore changes to the metabolic pathways of these bacteria, using a proteomics approach (two-dimensional electrophoresis and liquid chromatography-tandem mass spectrometry) combined with analyses of fermentable sugars and fermentation end products. The protein expression showed that even with an excess of glucose in all media, both strains could metabolize different carbohydrates simultaneously and that hexoses could also be used via a phosphoketolase pathway with preferential expression in liquid feed. Sugar analyses showed that the fermentation of sugars was homolactic for all media, with some heterolactic activity in liquid feed, as shown by the production of acetate. Cucumber juice (the medium with the highest glucose content) showed the lowest hexose consumption (10%), followed by liquid feed (33%) and MRS broth (50%). However, bacterial growth was significantly higher in cucumber juice and liquid feed than in MRS broth. This discrepancy was due to the growth benefit obtained from the utilization of the malate present in cucumber juice and liquid feed. Despite different growth conditions, the synthesis of essential cellular components and the stress response of the bacteria were unaffected. This study has improved our understanding of the mechanisms involved in the growth performance of an appropriate lactic acid bacterium strain to be used for food and feed fermentation, information that is of crucial importance to obtain a high-quality fermented product.

Aspergillus flavus growth inhibition by Lactobacillus strains isolated from traditional fermented Kenyan milk and maize products

Certain strains of lactic acid bacteria have been reported to inhibit fungal growth and may so be potential as biocontrol agents. In this study, 171 LAB strains were isolated from traditional fermented Kenyan milk and maize products and tested against aflatoxin-producing A. flavus fungi. The three LAB strains showing highest antifungal activity were identified as Lactobacillus plantarum. None of the strains were able to completely inhibit fungal growth under conditions favorable for fungi and suboptimal for LAB. These conditions probably reduced the growth and metabolic activity of some LAB isolates, as several growth-related aspects like production of antifungal biomolecules and other metabolites contribute to the inhibiting activity. The results suggest that certain LAB strains could be employed in food to control the growth of aflatoxigenic fungi. Further studies to establish the efficacy of the potential LAB strains in fermented products are in progress.