RESUMEN
A 12-kb region of the Streptococcus thermophilus CNRZ368 chromosome was found to contain two copies of IS981 (one complete and one truncated) and three copies of ISS1 (two complete, ISS1SA and ISS1SC, and one truncated, delta ISS1SB). Comparison of the nucleotide sequences of these ISS1 elements with those of previously identified iso-ISS1 elements from Lactococcus lactis and the Enterococcus genus indicated that the ISS1 group is divided into three distinct subgroups which we have named alpha, beta and gamma. Nucleotide sequences of elements belonging to the same subgroup share more than 97% identity whereas sequences of elements from different groups share only 75-85% identity. Sequence analysis of ISS1SA and delta ISS1SB showed that they are members of the alpha group. We found that ISS1SC from S. themophilus CNRZ368, an ISS1 from L. lactis IL964 and IS946 from L. lactis TEK1 resulted from recombinations between alpha and beta elements. In addition, ISS1W from L. lactis Wg2 resulted from a recombination event between a gamma element and an ISS1 belonging to an unidentified subgroup. ISS1 sequences belonging to the alpha and beta subgroups were found in both S. thermophilus and L. lactis and gamma sequences were found in both the Enterococcus genus and L. lactis. The quasi-identity of some ISS1 elements in S. thermophilus and L. lactis and the distribution of alpha and beta elements suggest that horizontal transfer of ISS1 elements recently took place from L. lactis to S. thermophilus, two lactic acid bacteria used in the manufacture of cheeses. Since the presence of IS981 in S. thermophilus CNRZ368 also probably resulted from a horizontal transfer from L. lactis [Guédon et al. (1995) Mol. Microbiol. 16, 69-78], the 12-kb region bearing IS981 and ISS1 elements could be due to the integration of a lactococcal DNA fragment into the chromosome.
Asunto(s)
Elementos Transponibles de ADN , Lactococcus lactis/genética , Streptococcus/genética , Secuencia de Bases , Mapeo Cromosómico , Elementos Transponibles de ADN/genética , ADN Bacteriano , Datos de Secuencia Molecular , MosaicismoRESUMEN
The nucleotide sequence of the 3' part of a ribosomal and transfer RNA locus from Streptococcus salivarius subsp thermophilus NST1403 was determined. The sequenced DNA fragment includes the 3' end of a 23S rRNA gene, a 5S rRNA gene, a tRNA(asn) gene and a potential transcriptional terminator. The tRNA gene does not encode for the CCA 3'terminus of mature tRNA. We compared this sequence to a promoter-carrying DNA fragment sequence (P20) of Streptococcus salivarius subsp thermophilus A054 [1]. We found that the P20 sequence included the 3' end of a 23S rRNA gene, a 5S rRNA gene and the 5' part of a tRNA(val) gene. The two 23S-5S spacer sequences are identical and contain a promoter and a potential 23S rRNA processing site. Therefore, 5S rRNA and tRNA genes could be transcribed from a promoter located within the 23S-5S spacer of at least two of the six rRNA loci.
Asunto(s)
ADN Ribosómico/genética , Regiones Promotoras Genéticas/genética , ARN Bacteriano/genética , Streptococcus/genética , Secuencia de Bases , Datos de Secuencia Molecular , ARN Ribosómico 23S/genética , ARN Ribosómico 5S/genéticaRESUMEN
Cloning and characterization of the gor gene of the lactic acid bacterium Streptococcus thermophilus, encoding glutathione reductase, are described in this paper. This enzyme is a part of the enzymatic defences against oxidative stress in eukaryotic cells and in Gram-negative bacteria, but was never found in Gram-positive bacteria before this study. The amino acid sequence shares extensive similarities with glutathione reductases from other organisms, e.g. 62% amino acid identity with Escherichia coli protein. Northern blot analysis and glutathione reductase enzyme assays gave evidence that the gene is expressed in aerobically growing cells.
Asunto(s)
ADN Bacteriano/química , Genes Bacterianos/genética , Glutatión Reductasa/genética , Streptococcus/genética , Secuencia de Bases , Northern Blotting , Clonación Molecular , ADN Bacteriano/genética , Electroforesis en Gel de Poliacrilamida , Glutatión Reductasa/farmacocinética , Técnicas In Vitro , Datos de Secuencia Molecular , Reacción en Cadena de la Polimerasa , Mapeo Restrictivo , Streptococcus/enzimología , Streptococcus/crecimiento & desarrolloRESUMEN
Three ribosomal probes from Streptococcus salivarius subsp. thermophilus were cloned. Sequence data demonstrate that their juxtaposition corresponds to an entire operon. They were used in order to study ribosomal operon number and organization. rRNA genes were shown to be clustered in the order 5'-16S-23S-5S-3' and the number of rrn loci to vary within the subspecies. The smallest of the 3 probes was used for strain characterization. Substantial variability in hybridization patterns was observed among strains, resulting not only from, restriction fragment length polymorphism (RFLP) but also from the variability of ribosomal operon number.
Asunto(s)
Sondas de ADN/análisis , ADN Ribosómico/genética , Polimorfismo Genético/genética , Streptococcus/genética , Autorradiografía , Secuencia de Bases/genética , Clonación Molecular , Hibridación Genética , Técnicas In Vitro , Datos de Secuencia Molecular , Streptococcus/clasificación , Operón de ARNr/genéticaRESUMEN
Genomic polymorphism in Streptococcus salivarius subsp. thermophilus was revealed by DNA restriction pattern analysis. A 4.2-kb variable DNA fragment was cloned from strain NST7 and hybridised with the DNA of 25 strains allowing an easy detection of intraspecific RFLP. Strong and weak hybridisation signals were observed and the latter were specifically revealed by a 2.1-kb fragment of the probe. Probe specificity was demonstrated by the absence of homology with DNA of strains belonging to 10 other species, with the exception of S. salivarius subsp. salivarius, confirming a close relationship between S. salivarius and S. thermophilus.
Asunto(s)
Polimorfismo de Longitud del Fragmento de Restricción , Streptococcus/genética , Clonación Molecular , Sondas de ADN , Enzimas de Restricción del ADN , ADN Bacteriano/genética , Hibridación de Ácido NucleicoRESUMEN
The three restriction endonucleases SfiI, BssHII, and SmaI were found to generate fragments with suitable size distributions for mapping the genome of Streptococcus thermophilus A054. A total of 5, 8, and 24 fragments were produced with SfiI, BssHII, and SmaI, respectively. An average genome size of 1,824 kb was determined by summing the total fragment sizes obtained by digestions with these three enzymes. Partial and multiple digestions of genomic DNA in conjunction with Southern hybridization were used to map SfiI, BssHII, and SmaI fragments. All restriction fragments were arranged in a unique circular chromosome. Southern hybridization analysis with specific probes allowed 23 genetic markers to be located on the restriction map. Among them, six rrn loci were precisely located. The area of the chromosome containing the ribosomal operons was further detailed by mapping some of the ApaI and SgrAI sites. Comparison of macrorestriction patterns from three clones derived from strain A054 revealed two variable regions in the chromosome. One was associated with the tandem rrnD and rrnE loci, and the other was mapped in the region of the lactose operon.
Asunto(s)
Genoma Bacteriano , Mapeo Restrictivo , Streptococcus/genética , Southern Blotting , Cromosomas Bacterianos , ADN Bacteriano/metabolismo , Desoxirribonucleasas de Localización Especificada Tipo II/metabolismo , Electroforesis en Gel de Campo Pulsado , Marcadores Genéticos , Variación Genética , Especificidad de la Especie , Streptococcus/clasificaciónRESUMEN
A chromosomal repeated sequence from Streptococcus thermophilus was identified as a new insertion sequence (IS), IS1191. This is the first IS element characterized in this species. This 1313 bp element has 28 bp imperfect terminal inverted repeats and is flanked by short direct repeats of 8 bp. The single large open reading frame of IS1191 encodes a 391-amino-acid protein which displays homologies with transposases encodes by IS1201 from Lactobacillus helveticus (44.5% amino-acid sequence identity) and by the other ISs of the IS256 family. One of the copies of IS1191 is inserted into a truncated iso-IS981 element. The nucleotide sequences of two truncated iso-IS981s from S. thermophilus and the sequence of IS981 element from Lactococcus lactis share more than 99% identity. The distribution of these insertion sequences in L. lactis and S. thermophilus strains suggests that intergeneric transfers occur during cocultures used in the manufacture of cheese.