Lactic acid bacteria (LAB) constitute a heterogeneous group of bacteria that are traditionally used to produce fermented foods. The industrialization of food transformations has increased the economical importance of LAB, as they play a crucial role in the development of the organoleptic and hygienic quality of fermented products. However, the strains selected for industrial purposes, should tolerate adverse conditions encountered in industrial processes, either during starter handling and storage (freeze-drying, freezing, or spray-drying) or during food processing in which abiotic stresses such as heat, cold, acidity, and high concentration of NaCl or ethanol are common. Wine LAB have to deal with several stresses including an acidic pH, a high alcoholic content, non optimal growth temperatures, and growth-inhibitory compounds such as fatty acids and tannins, originated from yeast and bacteria metabolism. Wine LAB have developed several mechanisms to escape or to tolerate wine conditions. They carry out a malolactic fermentation in this stressful environment. In addition to the regulation of the expression of specific genes, bacteria have evolved adaptive networks to face the challenges of a changing environment and to survive under conditions of stress. The so called Global Regulatory Systems control the simultaneous expression of a large number of genes in response to a variety of environmental stress factors. CIRCE sequences able to bind the HrcA repressor, sigma(B) dependent promoters and CtsR regulatory elements have been observed in several genes identified from wine LAB. Improved knowledge of regulators and a better understanding of LAB stress responses could constitute a basis of comparison with the well known model microorganisms, Escherichia coli and Bacillus subtilis. Moreover, it can provide an important insight into improving current industrial starter strains.

No abstract

Aims: Little genetic information exists on the ability of wine lactic acid bacteria (LAB) to hydrolyse glycoconjugates during malolactic fermentation. We tried to fill this important gap by characterizing a gene codifying for a putative b-glucosidase enzyme from wine Lactobacillus plantarum and from a commercial strain of Oenococcus oeni. Methods and Results:The coding region of the putative b-glucosidase gene is 1400 nucleotides long and started with an ATG codon. The gene is widespread among LAB and the highest identity was observed between the nucleotide of L. plantarum, Lactobacillus pentosus, Lactobacillus paraplantarum and O. oeni b-glucosidase gene. The protein sequence deduced from the isolated genes has a calculated molecular mass of 61AE19 kDa. Furthermore, the expression of the b-glucosidase gene in L. plantarum strain was analysed, under several stress, by reverse transcriptase (RT)-PCR and Northern-blot analysis. The gene was apparently regulated by abiotic stresses such as temperature, ethanol and pH. Conclusions: The b-glucosidase gene is widespread among LAB and its expression is probably regulated by a wide range of abiotic stresses. Significance and Impact of the Study: The inhibitory effect of temperature and ethanol on the L. plantarum b-glucosidase gene may be useful to explain the differences found in b-glucosidase activity reported in wines by several authors.

S . M AS S A, C. A LT IE R I, V. Q UA RA N TA AN D R. DE P AC E. 1997. Cow's milk was inoculated with ca 10 3 and 10 7 cfu ml −1 Escherichia coli O157 : H7. After fermentation at 42°C for 0-5 h, the yoghurt was stored at 4°C. Two kinds of yoghurt were used : traditional yoghurt (TY), made with Streptococcus thermophilus and Lactobacillus bulgaricus starter cultures, and 'bifido' yoghurt (BY), made with the two starter cultures plus Bifidobacterium bifidum. After 7 d E. coli O157 : H7 decreased from 3·52 to 2·72 log 10 cfu ml −1 and from 7·08 to 5·32 log 10 cfu ml −1 in TY, and from 3·49 to 2·73 log 10 cfu ml −1 and from 7·38 to 5·41 log 10 cfu ml −1 in BY. The pH values of yoghurt dropped from 6·6 to 4·5 and 4·4 in TY (for low and high pathogen inocula, respectively), and from 6·6 to 4·6 and 4·5 in BY (for low and high pathogen inocula, respectively).

No abstract