Genome analysis of lactic acid bacteria in food fermentations and biotechnological applications

Host recognition by lactic acid bacterial phages

Bacteriophage infection of lactic acid bacteria (LAB) is one of the most significant causes of inconsistencies in the manufacture of fermented foods, affecting production schedules and organoleptic properties of the final product. Consequently, LAB phages, and particularly those infecting Lactococcus lactis, have been the focus of intensive research efforts. During the past decade, multidisciplinary scientific approaches have uncovered molecular details on the exquisite process of how a lactococcal phage recognises and binds to its host. Such approaches have incorporated genomic/molecular analyses and their partnership with phage structural analysis and host cell wall biochemical studies are discussed in this review, which will also provide our views on future directions of this research field.

Characterization of a novel SGNH-type esterase from Lactobacillus plantarum

Lactic acid bacteria (LAB) are sources of a large variety of microbial ester hydrolases because they can produce a wide range of short-chain esters, phenolic alcohols, and fatty acids. Here, a novel SGNH-type esterase (LpSGNH1) from Lactobacillus plantarum WCFS1 was identified, functionally characterized, and immobilized for biotechnological applications. Homologs of LpSGNH1 are also found in many lactic acid bacteria (LAB) species. Biochemical features of LpSGNH1 were investigated using mass spectrometry, gel filtration chromatography, enzyme kinetics, fluorescence, and circular dichroism (CD) spectroscopy. LpSGNH1 were retained its activity under conditions that would be encountered during fermentations. Interestingly, LpSGNH1 exhibited the ability to act on a broad range of substrates including ketoprofen acetate, cefotaxime (CTX), and 7-aminocephalosporanic acid (7-ACA) as well as glucose pentaacetate, acetylxylan, and acetylalginate, which make LpSGNH1 a great candidate for extensive industrial applications. Furthermore, cross-linked enzyme aggregates of LpSGNH1 (CLEA-LpSGNH1) displayed recycling ability and thermal stability compared to free LpSGNH1, which could be useful for industrial applications. This work highlights the importance of LpSGNH1 in the preparation of commercial compounds, and LpSGNH1 can be used as a model system of SGNH esterases in lactic acid bacteria.

Probiotics and its functionally valuable products-a review

During the past two decades probiotic bacteria have been increasingly proposed as health promoting bacteria in variety of food system, because of its safety, functional, and technological characteristics. Commonly, Lactobacillus spp., Bifidobacterium spp., Saccharomyces boulardii, and some other microorganisms have been considered as probiotic strains. Possibly these bacterial strains exerted several beneficial effects into gastrointestinal tract of host while administered with variety of food system. Lactic acid bacteria (LAB) usually produce antimicrobial substances like bacteriocin which have broad spectrum of antagonist effect against closely related Gram positive and Gram negative pathogens. LAB strains often produce polymeric substances such as exopolysaccharides (EPS) which increase the colonization of probiotic bacteria by cell-cell interactions in gastrointestinal tract. LAB also produces biosurfactant which showed that the wide range of antimicrobial activity against bacterial pathogen as well as its antiadhesive properties reduces the adhesion of pathogens into gastric wall membrane. Furthermore, LAB strains have also been reported for production of antioxidants which are ability to scavenge the free radicals such as superoxide anions and hydroxyl radicals. For this sense, this review article is mainly focused on the ecology, biosynthesis, genetics, target sites, and applications of bacteriocins and EPS from LAB strains. Moreover, this review discusses about the production and functions of nutritive essential element folate and iron chelating agent such as siderophores from LAB.

Live recombinant Lactococcus lactis vaccine expressing aerolysin genes D1 and D4 for protection against Aeromonas hydrophila in tilapia (Oreochromis niloticus)

AIMS

To evaluate a live recombinant Lactococcus lactis vaccine expressing aerolysin genes D1 (Lac-D1ae) and/or D4 (Lac-D4ae) in protection against Aeromonas hydrophila in tilapia (Oreochromis niloticus).

METHODS AND RESULTS

The polymerase chain reaction (PCR)-amplified 250- and 750-bp sequences coding for domains D1 and D4 of aerolysin were individually cloned into pNZ8048 and electrotransformed into L. lactis. The recombinant vaccine candidates were then either orally fed or injected intraperitoneally into tilapia. The development of antibodies in sampled fish compared to control groups implied that the recombinant epitopes expressed in L. lactis were able to elicit an immunogenic response in tilapia. Interestingly, the lower doses of both Lac-D1ae and Lac-D4ae gave higher antibody levels over the study period. Fish immunized with Lac-D1ae and Lac-D4ae together showed the highest level of protection, and the mortality was reduced significantly compared to control strains in both modes of vaccination.

CONCLUSIONS

The recombinant L. lactis strain expressing D1 and D4 produced aerolysin-specific serum IgM in tilapia. Both D1 and D4 promoted 55-82% relative per cent survival (RPS) against Aeromonas infection through intraperitoneal injection, whereas the RPS following oral feeding of the vaccine was 70-100%.

SIGNIFICANCE AND IMPACT OF THE STUDY

The D1 and D4 regions of the aerolysin protein have been successfully identified as immunogenic regions that can elicit antibody production in tilapia and protect against challenge with Aer. hydrophila. A promising oral vaccine using L. lactis harbouring the D1 and D4 regions has been developed to control Aer. hydrophila.

Biopreservation of refrigerated and vacuum-packed Dicentrarchus labrax by lactic acid bacteria

Two lactic acid bacteria (LAB) were selected from 100 LAB isolated from various sea products to examine their use in Dicentrarchus labrax preservation. The isolates, tentatively named strain nr 3 and 7, were identified as Lactobacillus plantarum and L. pentosus, respectively. They showed antagonistic activity against psychrotroph, pathogenic, and coliform bacteria. The antagonistic activity of strain 3 was suggested to be by bacteriocins since activity was abolished by protease treatment, while that of strain 7 was due to the effect of pH decrease caused by the produced organic acids. Their use prevented total volatile basic nitrogen contents (TVB-N) and trimethylamine (TMA) to some extent, suggesting that inoculation could extend the period of storage.

CcpA affects expression of the groESL and dnaK operons in Lactobacillus plantarum

Background

Lactic acid bacteria (LAB) are widely used in food industry and their growth performance is important for the quality of the fermented product. During industrial processes changes in temperature may represent an environmental stress to be overcome by starters and non-starters LAB. Studies on adaptation to heat shock have shown the involvement of the chaperon system-proteins in various Gram-positive bacteria. The corresponding operons, namely the dnaK and groESL operons, are controlled by a negative mechanism involving the HrcA repressor protein binding to the cis acting element CIRCE.

Results

We studied adaptation to heat shock in the lactic acid bacterium Lactobacillus plantarum. The LM3-2 strain, carrying a null mutation in the ccpA gene, encoding the catabolite control protein A (CcpA), showed a lower percent of survival to high temperature with respect to the LM3 wild type strain. Among proteins differentially expressed in the two strains, the GroES chaperon was more abundant in the wild type strain compared to the mutant strain under standard growth conditions. Transcriptional studies showed that class I heat shock operons were differentially expressed upon heat shock in both strains. Indeed, the dnaK and groESL operons were induced about two times more in the LM3 strain compared to the LM3-2 strain. Analysis of the regulatory region of the two operons showed the presence of cre sequences, putative binding sites for the CcpA protein.

Conclusion

The L. plantarum dnaK and groESL operons are characterized by the presence of the cis acting sequence CIRCE in the promoter region, suggesting a negative regulation by the HrcA/CIRCE system, which is a common type of control among the class I heat shock operons of Gram-positive bacteria. We found an additional system of regulation, based on a positive control exerted by the CcpA protein, which would interact with cre sequences present in the regulatory region of the dnaK and groESL operons. The absence of the CcpA protein results in a lower induction of the chaperon coding operons, with a consequent lower percent of survival of the LM3-2 mutant strain population with respect to the wild type when challenged with a heat insult.