Streptococcus thermophilus strain CNRZ 302 is unable to ferment galactose, neither that generated intracellularly by lactose hydrolysis nor the free sugar. Nevertheless, sequence analysis and complementation studies with Escherichia coli demonstrated that strain CNRZ 302 contained structurally intact genes for the Leloir pathway enzymes. These were organized into an operon in the order galKTE, which was preceded by a divergently transcribed regulator gene, galR, and followed by a galM gene and the lactose operon lacSZ. Results of Northern blot analysis showed that the structural gal genes were transcribed weakly, and only in medium containing lactose, by strain CNRZ 302. However, in a spontaneous galactose-fermenting mutant, designated NZ302G, the galKTE genes were well expressed in cells grown on lactose or galactose. In both CNRZ 302 and the Gal ؉ mutant NZ302G, the transcription of the galR gene was induced by growth on lactose. Disruption of galR indicated that it functioned as a transcriptional activator of both the gal and lac operons while negatively regulating its own expression. Sequence analysis of the gal promoter regions of NZ302G and nine other independently isolated Gal ؉ mutants of CNRZ 302 revealed mutations at three positions in the galK promoter region, which included substitutions at positions ؊9 and ؊15 as well as a single-base-pair insertion at position ؊37 with respect to the main transcription initiation point. Galactokinase activity measurements and analysis of gusA reporter gene fusions in strains containing the mutated promoters suggested that they were gal promoter-up mutations. We propose that poor expression of the gal genes in the galactose-negative S. thermophilus CNRZ 302 is caused by naturally occurring mutations in the galK promoter.After its discovery almost 40 years ago, the Escherichia coli lactose operon, encoding enzymes of lactose metabolism, became the first model for gene regulation (reviewed in reference 4). The key component of this system is the lac repressor (LacI), the product of the lacI gene. The lac operon contains a primary operator (O 1 ), which is the major element of repression by LacI, and two pseudo-operators, which enhance repressor binding to O 1 by cooperativity. Control of the lac operon also involves activation by the cyclic AMP receptor protein.Many other paradigm systems of negative control have since been described, including GalR, one of the two repressors of the gal regulon encoding enzymes of galactose transport and metabolism in E. coli. Regulation of the gal regulon is mediated through GalR, GalS (Gal isorepressor), and the cyclic AMP receptor protein. GalR and GalS negatively regulate transcription of the two promoters of the gal operon, although GalS is not as efficient as GalR (57).The bioconversion of lactose, which is the primary carbon and energy source in milk, into lactic acid is an essential process in industrial dairy fermentations carried out by lactic acid bacteria. Genetic studies of the metabolic pathways for lactose utilization i...

Streptococci from different collections and dairy materials were characterized by conventional and molecular methods. After amplification of the 16S-23S rDNA spacer region, all the strains referable to the genus Streptococcus exhibited a single polymerase chain reaction (PCR) product, allowing their differentiation from enterococci. Cleaving this PCR product with Hae III, two different restriction patterns could be observed, allowing Streptococcus salivarius DSM 20560T, Strep. thermophilus NCDO 822 and two strains of Streptococcus spp. to be gathered in one group and all the other strains in another. In order to achieve strain typing, all the cultures were investigated by random amplified polymorphic DNA (RAPD)-PCR analysis employing two selected primers. The results were treated by cluster analysis, appearing significantly consistent with both the taxonomic position and the origin of the strains. Pulsed-field gel electrophoresis (PFGE) of Sma I digests of the genomic DNA from 11 representative strains with decreasing levels of RAPD similarity allowed their diversity to be confirmed, even though RAPD-PCR proved to be less discriminating than PFGE analysis. The results are discussed with reference to the capability of the analytical procedures used to aid both identification and strain typing of streptococci, as well as the taxonomic structure of the species Strep. thermophilus.

The results of a study on texture evolution during 35 days of storage of ttamaretti", a typical Italian cookie, packaged in two different ways are reported. Amaretti cookies were wrapped in polyvinylchloride (pvq film or aluminium foil (ALL), to simulate two different permeability conditions and stored at controUed temperature and humidity. Evolution of texture (such as hardness) and a.. were tested instrumentally by a texture analyser and a hygrometer, respectively. Texture was assessed by a cut and puncturing test. Indices for hardening were area under the curve (N x mm) and gradient (N/mm) for the puncturing test and maximum force (N) for the cut test. Both textural tests showed significandy higher hardening of PVC cookies, compared to the ALL cookies. The latter retained good sensorial propenies at the end of the storage period, although their internal structure changed from soft and moist to mealy, while the PVC cookies were no longer edible only 10 days after baking. Aw values decreased and increased in PVC and AIL lots, respectively. The tesults suggest that hardening may be explained by water loss in PVC and moisture redistribution in AIl...

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Scotta is the main by-product in the making of ricotta cheese. It is widely produced in southern Europe and particularly in Italy where it represents a serious environmental pollutant due to its high lactose content. With the aim of evaluating whether scotta bioconversion into lactic acid can be considered as an alternative to its disposal, besides providing it with an added value, here the growth, fermentative performances, and lactic acid productions of pure and mixed cultures of Lactobacillus casei, Lactobacillus helveticus, and Streptococcus thermophilus were evaluated on ovine scotta-based media, without and with the addition of nutritional supplements. The outcomes indicate that ovine scotta can be utilized for the biotechnological production of lactic acid with yields up to 92%, comparable to those obtained on cheese-whey. Indeed, the addition of nutritional supplements generally improves the fermentative performances of lactic acid bacteria leading to about 2 g l(-1) h(-1) of lactic acid. Moreover, the use of mixed cultures for scotta bioconversion reduces the need for nutritional supplements, with no detrimental effects on the productive parameters compared to pure cultures. Finally, by using L. casei and S. thermophilus in pure and mixed cultures, up to 99% optically pure L: -lactic acid can be obtained.