María Pía Taranto

B-group vitamin production by lactic acid bacteria--current knowledge and potential applications.

Although most vitamins are present in a variety of foods, human vitamin deficiencies still occur in many countries, mainly because of malnutrition not only as a result of insufficient food intake but also because of unbalanced diets. Even though most lactic acid bacteria (LAB) are auxotrophic for several vitamins, it is now known that certain strains have the capability to synthesize water‐soluble vitamins such as those included in the B‐group (folates, riboflavin and vitamin B12 amongst others). This review article will show the current knowledge of vitamin biosynthesis by LAB and show how the proper selection of starter cultures and probiotic strains could be useful in preventing clinical and subclinical vitamin deficiencies. Here, several examples will be presented where vitamin‐producing LAB led to the elaboration of novel fermented foods with increased and bioavailable vitamins. In addition, the use of genetic engineering strategies to increase vitamin production or to create novel vitamin‐producing strains will also be discussed. This review will show that the use of vitamin‐producing LAB could be a cost‐effective alternative to current vitamin fortification programmes and be useful in the elaboration of novel vitamin‐enriched products.

Lactobacillus reuteri CRL1098 Produces Cobalamin

We found that Lactobacillus reuteri CRL1098, a lactic acid bacterium isolated from sourdough, is able to produce cobalamin. The sugar-glycerol cofermentation in vitamin B(12)-free medium showed that this strain was able to reduce glycerol through a well-known cobalamin-dependent reaction with the formation of 1,3-propanediol as a final product. The cell extract of L. reuteri corrected the coenzyme B12 requirement of Lactobacillus delbrueckii subsp. lactis ATCC 7830 and allowed the growth of Salmonella enterica serovar Typhimurium (metE cbiB) and Escherichia coli (metE) in minimal medium. Preliminary genetic studies of cobalamin biosynthesis genes from L. reuteri allowed the identification of cob genes which encode the CobA, CbiJ, and CbiK enzymes involved in the cobalamin pathway. The cobamide produced by L. reuteri, isolated in its cyanide form by using reverse-phase high-pressure liquid chromatography, showed a UV-visible spectrum identical to that of standard cyanocobalamin (vitamin B12).

Heterofermentative pattern and exopolysaccharide production by Lactobacillus helveticus ATCC 15807 in response to environmental pH

Aims: The objective of this work was to evaluate the fermentation pattern of and the exopolysaccharide (EPS) production by Lactobacillus helveticus ATCC 15807 in milk batch cultures under controlled pH (4·5, 5·0 and 6·2).

Bile salts and cholesterol induce changes in the lipid cell membrane of Lactobacillus reuteri.

Aims: The objective of this study was to evaluate the effect of bile salts and cholesterol in the lipid profile of Lactobacillus reuteri CRL 1098 and to determine the relationship existing between these changes: the in vitro removal of cholesterol and the tolerance of the cells to acid and cold stress.

Homemade traditional cheeses for the isolation of probiotic Enterococcus faecium strains

One hundred twenty-two strains of Enterococcus faecium isolated from Tafí Cheese, a homemade traditional cheese of the highlands in the province of Tucumán, Argentina, were evaluated for their potential application as starter cultures in the manufacture of this traditional cheese. Eleven of the 122 strains showing limited delays in growth in oxgall were selected for the study of bile salts hydrolase activity (BSH), cholesterol reduction, antimicrobial activity, and virulence determinants. Nine strains were able to remove cholesterol in in vitro assays, a property that was closely related to the bile salt hydrolase activity. Only two strains produced active bacteriocins against Listeria strains although genetic evidence for the bacteriocin structural gene was found in six other enterococci strains. No virulence factors were detected in any of the 11 selected strains of enterococci.

Structural Characterization of the Active Site of the PduO-Type ATP:Co(I)rrinoid Adenosyltransferase from Lactobacillus reuteri

The three-dimensional crystal structure of the PduO-type corrinoid adenosyltransferase from Lactobacillus reuteri (LrPduO) has been solved to 1.68-Å resolution. The functional assignment of LrPduO as a corrinoid adenosyltransferase was confirmed by in vivo and in vitro evidence. The enzyme has an apparent \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(K_{m}^{\mathrm{ATP}}\) \end{document} of 2.2 μm and \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(K_{m}^{\mathrm{Cobalamin}}\) \end{document} of 0.13 μm and a kcat of 0.025 s-1. Co-crystallization of the enzyme with Mg-ATP resulted in well-defined electron density for an N-terminal loop that had been disordered in other PduO-type enzyme structures. This newly defined N-terminal loop makes up the lower portion of the enzyme active site with the other half being contributed from an adjacent subunit. These results provide the first detailed description of the enzyme active site for a PduO-type adenosyltransferase and identify a unique ATP binding motif at the protein N terminus. The molecular architecture at the active site offers valuable new insight into the role of various residues responsible for the human disease methylmalonic aciduria.

Bile salts hydrolase plays a key role on cholesterol removal by Lactobacillus reuteri

The [ H]cholesterol removal by Lactobacillus reuteri was due to a co-precipitation together with unconjugated bile acids, which was linked to the bile salt hydrolase activity of the cells. No [ H]cholesterol was found inside the cells indicating that no assimilation occurred.

Lactobacillus reuteri CRL 1098 prevents side effects produced by a nutritional vitamin B12 deficiency

Aims:  To evaluate the efficiency of the vitamin B12‐producing Lactobacillus reuteri CRL1098 strain in preventing the symptoms caused by a nutritional cobalamin‐deficient diet in pregnant female mice and their weaned offspring.

Genome Sequence of the Bacteriocin-Producing Lactobacillus curvatus Strain CRL705

Lactobacillus curvatus is one of the most prevalent lactic acid bacteria found in fermented meat products. Here, we present the draft genome sequence of Lactobacillus curvatus CRL705, a bacteriocin producer strain isolated from an Argentinean artisanal fermented sausage, which consists of 1,833,251 bp (GC content, 41.9%) and two circular plasmids of 12,342 bp (pRC12; GC, 43.9%) and 18,664 bp (pRC18; GC, 34.4%).

Adaptive acid tolerance response in Lactobacillus acidophilus

Stationary phase cultures of Lactobacillus acidophilus CRL 639 are naturally acid resistant to pH 3.0 while exponential phase cells induce an acid tolerance response upon exposure to sublethal pH (3.8–6.0). Maximal response was achieved after adaptation at pH 4.2 and pH 5.0. Protein synthesis was required in the latter case.