Ecology of the Lactic Streptococci. A Review1

Sandine, W. E.; Radich, Paul Christian; Elliker, P. R.

doi:10.4315/0022-2747-35.3.176

Cited by 100 publications

(40 citation statements)

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“…Identification of the splice junction indicates that the Ll.ltrB intron spans 2,492 nucleotides and is similar in size to other ORF-containing group II introns (26,31,44). Ll.ltrB does not appear to be a recent genetic acquisition in lactococci, since the G/C ratio of the complete intron (36%) and codon usage for ltrA are consistent with lactococcal genomes (codon usage for ltrA is most similar to a codon usage table complied from L. lactis genes as determined by CODONPREFERENCE provided by GCG) (6,46). A combination of comparative analysis and computer modeling of the lactococcal intron RNA secondary structure revealed that Ll.ltrB can be folded into the six RNA secondarystructure domains common to group II introns (31) (Fig.…”

Section: Splicing Of the Lactococcal Intron In Vivomentioning

confidence: 84%

Splicing of a group II intron involved in the conjugative transfer of pRS01 in lactococci

1996

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Analysis of a region involved in the conjugative transfer of the lactococcal conjugative element pRS01 has revealed a bacterial group II intron. Splicing of this lactococcal intron (designated Ll.ltrB) in vivo resulted in the ligation of two exon messages (ltrBE1 and ltrBE2) which encoded a putative conjugative relaxase essential for the transfer of pRS01. Like many group II introns, the Ll.ltrB intron possessed an open reading frame (ltrA) with homology to reverse transcriptases. Remarkably, sequence analysis of ltrA suggested a greater similarity to open reading frames encoded by eukaryotic mitochondrial group II introns than to those identified to date from other bacteria. Several insertional mutations within ltrA resulted in plasmids exhibiting a conjugative transfer-deficient phenotype. These results provide the first direct evidence for splicing of a prokaryotic group II intron in vivo and suggest that conjugative transfer is a mechanism for group II intron dissemination in bacteria.Conjugation is an important mode of genetic exchange in bacteria. The specific mechanism of DNA transfer comprises two distinct functions, one being the enzymatic preparation of the plasmid DNA prior to replicative transfer and another involving formation of the mating channel through which DNA is transferred into a recipient cell. Initiation of plasmid transfer requires a single-stranded cleavage at a specific origin of transfer (oriT) produced by the action of a specialized nucleoprotein complex called a relaxosome (53). In many conjugative systems, transfer origins are flanked by genes involved in the formation of a functional relaxosome complex. One key feature of an oriT region is the ability of the region to confer mobilization in cis, provided the remaining transfer functions are present in trans.The conjugative element pRS01 from Lactococcus lactis subsp. lactis ML3 and the sex factor from L. lactis subsp. lactis 712 are prototypical mobile elements in lactococci (15, 50). Both elements have been shown to mediate high-frequency transfer of genes encoding lactose utilization (Lac ϩ ) by insertion sequence-directed conintegration with nonconjugative Lac ϩ plasmids (19,40). In addition, both elements confer a cell aggregation (Clu) phenotype (16, 52) associated with highfrequency conjugative transfer. Previous genetic analysis of these elements has identified the gene responsible for the aggregation phenotype (clu) associated within an inversion region (2, 20, 21). To date, however, the oriT and gene(s) encoding relaxosome components of pRS01 have not been localized within either element. In an effort to exploit conjugation as a means of lactococcal strain development, we have characterized the transfer regions of pRS01 by insertional mutagenesis via IS946-mediated cointegration with the 11-kb plasmid pTRK28 (43) (for a representation of pTRK28:: pRS01 cointegration, see Fig. 1 in reference 33). Analysis of the insertion site junctions of pRS01::pTRK28 cointegrate plasmids identified four distinct regions of pRS01 involved...

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Section: Splicing Of the Lactococcal Intron In Vivomentioning

confidence: 84%

Splicing of a group II intron involved in the conjugative transfer of pRS01 in lactococci

1996

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“…In an attempt to study evolution of genetic defects which underlie nutritional deficiencies, we decided to characterize the inability of Lactococcus lactis to synthesize certain amino acids. L. lactis dairy fermentations strains are believed to derive from plant strains, which were introduced in a novel and relatively rich ecological niche, milk (38). Dairy strains seem to have acquired features which adapted them to milk, such as capacity to utilize lactose via a phosphotransferase system (10) and to degrade casein by a cell wall protease (22).…”

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confidence: 99%

Gene inactivation in Lactococcus lactis: branched-chain amino acid biosynthesis

et al. 1993

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The Lactococcus lactis subsp. lactis strains isolated from dairy products are auxotrophs for branched-chain amino acids (leucine, isoleucine, and valine), while most strains isolated from nondairy media are prototrophs. We have cloned and sequenced the leu genes from one auxotroph, IL1403. The sequence is 99% homologous to that of the prototroph NCDO2118, which was determined previously. Two nonsense mutations and two small deletions were found in the auxotroph sequence, which might explain the branched-chain amino acid auxotrophy. Nevertheless, the leu genes from the auxotroph appear to be transcribed and regulated similarly to those from the prototroph.

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“…Cependant Lactococcus lactis se distingue de l'archétype bactérien par quatre traits singuliers: c'est une bactérie Gram positive, mésophile, microaérophile qui a emprunté des voies évolutives distinctes de celle des protéobactéries ; son GC % est bas, 34 à 38 % (Sandine et al, 1972) contre 48 à 52 % pour E coli (Brenner, 1984) ; son génome est de petite taille: de 2 à 2,7 MB (Le Bourgeois et al, 1989 ;Tanskanen et al, 1990), alors qu'il est de 4,2 à 4,5 MB chez E coli. Enfin sa niche écologique, le lait, les produits laitiers, est éloignée de celle des bactéries entériques (Sandine et al, 113 1972) ; L lactis y est soumis, au cours des processus de biotransformation auxquels il participe à de nombreuses sautes thermiques.…”

Section: Introductionunclassified

Les protéines de choc thermique chez Lactococcus lactis : synthèse et régulation ; thermotolérance

Boutibonnes

1996

Lait

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Résumé -On retrouve chez Lactococcus lactis les deux composantes habituelles de la réponse au choc thermique: la synthèse d'un petit nombre de protéines spécifiques dites hsps (pour «heet shock proteins») et l'élévation phénotypique de la résistance naturelle à la chaleur dite thermotolérance. Le passage brutal de 30 à 40 "C s'accompagne de l'amplification de la synthèse de 13 à 16 protéines parmi lesquelles sont reconnues par immunodétection sept protéines homologues des hsps d'Escherichia coli (ClpB, DnaJ, Dnak, GroEL,GrpE, Lon) et de Bacillus subtilis (J'I3). Six des gènes codant pour ces polypeptides-clés, surexprimés après l'élévation thermique, ont été clonés et séquencés ; trois d'entre eux ont été localisés sur le chromosome; ils montrent d'assez faibles différences avec leurs modèles bactériens déjà identifiés. La régulation de leur expression semble assez proche de celle des gènes thermorégulés de B subtilis. La thermotolérance s'exprime dans des conditions voisines; elle est maximale à 42 "C lorsque la température d'épreuve est de 52 "C. Toutefois les deux phénomènes ne sont pas induits par les mêmes agents "stressants» thermomimétiques. Comme chez les autres organismes ou cellules (eucaryotes et procaryotes), il est difficile de lier par un strict principe de causalité l'apparition de ce petit jeu de protéines à l'exhaussement de la résistance à la chaleur, déclenchés tous deux par des températures infra-létales. Lactococeus laetis 1 protéine de choc thermique 1thermotolérance

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Ecology of the Lactic Streptococci. A Review1

Cited by 100 publications

References 0 publications

Splicing of a group II intron involved in the conjugative transfer of pRS01 in lactococci

Splicing of a group II intron involved in the conjugative transfer of pRS01 in lactococci

Gene inactivation in Lactococcus lactis: branched-chain amino acid biosynthesis

Les protéines de choc thermique chez Lactococcus lactis : synthèse et régulation ; thermotolérance

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