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At least 1,405 records · Page 78Linked to original sources
PubMed2003

[Food-grade expression of human Cu/Zn-superoxide dismutase gene in Lactococcus lactis].

A food-grade gene expression system in L. lactis using the lacF gene as selection marker was constructed and further used for food-grade expression of human Cu/Zn superoxide dismutase (Cu/Zn SOD). Firstly, an integrative plasmid pUCEmDE containing homologous fragments with 0.5 kb flank sequences of the lacF gene was constructed. The lacF gene was in-frame deleted by double cross-over between the plasmid pUCEmDE and the chromosomal DNA in L. lactis MG5267 and resulted in a food-grade host WZ103 that was confirmed by PCR and Lac phenotype examination. After that, a complementary plasmid pMG36eF in which the lacF gene was controlled by the strong constitutive promoter P32 was electroporated into WZ103 and resulted in the restoration of Lac+ phenotype, indicating that the lacF function in WZ103 could be complemented by the lacF gene in pMG36eF. Finally, a food-grade plasmid pWZ104 used for the expression of Cu/Zn SOD was constructed, in which the lacF gene was used as a selective marker instead of any antibiotic resistance genes. Expressed Cu/Zn SOD in WZ103 (pWZ104) was demonstrated and showed biological activity through non-denatured PAGE and SOD activity gel-staining.

Food Microbiology↗
PubMed1993

Structure, organization, and expression of the lct gene for lacticin 481, a novel lantibiotic produced by Lactococcus lactis.

The structural gene for the lactococcal lantibiotic lacticin 481 (lct) has been identified and cloned using a degenerated 20-mer DNA oligonucleotide based on the amino-terminal 7 amino acid residues of the purified protein. The transcription of the lct gene was analyzed, and its promoter was mapped. DNA sequence analysis of the lct gene revealed an open reading frame encoding a peptide of 51 amino acids. Comparison of its deduced amino acid sequence with the amino-terminal sequence and the amino acid composition of lacticin 481 indicates that the 51-residue peptide is prelacticin 481, containing a 27-residue carboxyl-terminal propeptide and a 24-residue amino-terminal leader peptide which lacks the properties of a typical signal sequence and which is significantly different from the leaders of other lantibiotics. The predicted amino acid sequence of prolacticin 481 contains 3 cysteines, 2 serines, and 2 threonines which were not detectable in amino acid analyses of mature lacticin 481. Based on these results and on characterization by two-dimensional NMR techniques, a structural model is proposed in which 2 cysteine residues are involved in lanthionine and one in beta-methyllanthionine formation, and a 4th threonine residue is dehydrated. This model predicts a molecular mass for lacticin 481 of 2,901, which is in excellent agreement with that obtained from mass spectrometry.

Amino Acid Sequence↗
PubMed1996

Genetic determinants for the biosynthesis of nisin, a bacteriocin produced by Lactococcus lactis.

In the past, the genetic determinants for nisin biosynthesis were thought to be plasmid-located. However, it has been shown that production of nisin, immunity to nisin, and other properties such as the fermentation of sucrose, are encoded on 70 kb conjugative transposons that are chromosomally located. The extrachromosomal location of the nisin genes has not been substantiated by experiments that unequivocally show plasmid transfer. Two natural variants of nisin have been identified, nisin A and nisin Z, encoded by the genes nisA and nisZ, respectively. Both genes have been cloned and sequenced and differ only in a single base pair. Approximately 12 kb downstream from the structural gene has been cloned and sequenced, and a further 10 genes involved in the biosynthesis of nisin have been identified. The nisB and nisC gene products are involved in nisin maduration, the nisT in its secretion and the nisP in its processing. The nisR and nisK gene products have a regulatory role and the nisI, nisF, nisE and nisG are involved in immunity to nisin. All these genes display significant homology to the corresponding genes of the related lantibiotics subtilin and epidermin.

Amino Acid Sequence↗
PubMed1991

Microtiter plate assays for the measurement of phage adsorption and infection in Lactococcus and Enterococcus.

Three easy and rapid microtiter plate assays for determining phage sensitivity of lactococci and enterococci have been developed. In the microlysis assay, the degree of sensitivity was measured on the basis of the ability of the bacterial cells to grow in the presence of various concentrations of phage and to effect a color change of an acid-base indicator as a result of acid production. Two assays that specifically measure phage adsorption to bacterial cells have been developed on the basis of the enzyme-linked immunosorbent assay (ELISA) technique. In the direct phage adsorption ELISA, adsorption of phage particles to cells immobilized onto microtiter plate wells was measured using specific anti-phage antibody. In the competitive phage adsorption ELISA, phage adsorption was assayed by allowing phage to compete with specific antibody binding to the bacterial cell surface. All three assays were quantifiable photometrically.

Adsorption↗