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  • 1
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Sorbitol is claimed to have important health-promoting effects and Lactobacillus casei is a lactic acid bacterium relevant as probiotic and used as a cheese starter culture. A sorbitol-producing L. casei strain might therefore be of considerable interest in the food industry. A recombinant strain of L. casei was constructed by the integration of a d-sorbitol-6-phosphate dehydrogenase-encoding gene (gutF) in the chromosomal lactose operon (strain BL232). gutF expression in this strain followed the same regulation as that of the lac genes, that is, it was repressed by glucose and induced by lactose. 13C-nuclear magnetic resonance analysis of supernatants of BL232 resting cells demonstrated that, when pre-grown on lactose, cells were able to synthesize sorbitol from glucose. Inactivation of the l-lactate dehydrogenase gene in BL232 led to an increase in sorbitol production, suggesting that the engineered route provides an alternative pathway for NAD+ regeneration.
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 222 (2003), S. 0 
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: An expression vector for Lactobacillus casei has been constructed containing the inducible lac promoter and the gene encoding ultraviolet visible green fluorescent protein (GFPUV) as reporter. Different conditions to grow L. casei were assayed and fluorescence as well as total protein synthesized were quantified. The maintenance of neutral pH had the greatest incidence on GFPUV expression, followed by aeration and a temperature of 30°C. Environmental factors favoring GFPUV accumulation did not exactly correlate with those enhancing fluorescence. Therefore, oxygenation, by stirring the culture, had the greatest influence on the proportion of fluorescent protein, which is in accordance with the structural requirements of this protein. The highest yield obtained was 1.3 μg of GFP per mg of total protein, from which 55% was fluorescent.
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  • 3
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Sugar uptake and phosphoenolpyruvate phosphorylation assays have shown that the heterofermentative strain Lactobacillus reuteri CRL 1098, of likely probiotic value, can transport D-fructose through an inducible fructose-specific phosphotransferase system (Km 95 μM) and D-glucose mainly through a proton motive force-driven permease. These data open new perspectives for metabolic and regulatory studies in this bacterium.
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 203 (2001), S. 0 
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Secretion of the VP8* subunit of the VP4 capsid protein of rotavirus by Lactococcus lactis has been achieved. For this purpose, a secretion vector has been constructed with the lactococcal signal sequence AL9 and the VP8*-encoding gene fragment. The amount of VP8* secreted by L. lactis in the culture supernatant was quantified and visualised by Western blot. Furthermore, it was shown to retain its hemagglutination capability, indicating that the conformation of the secreted peptide may be retaining its biological activity.
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 148 (1997), S. 0 
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The chromosomally encoded lactose-specific phosphoenol pyruvate-dependent phosphotransferase system (PTS) has been investigated in Lactobacillus casei ATCC 393 [pLZ15-] and it was considered an excellent system to study the regulation of the lactose operon. This chromosomal operon has been cloned and sequenced, being 99% homologous to that encoded on the plasmid pLZ64. Expression of the lactose operon in different mutants of L. casei ATCC 393 [pLZ15−] and primer extension analysis revealed that it is subject to a dual regulation: (i) glucose repression possibly mediated by CcpA and PTS elements, and (ii) induction by lactose through transcriptional antitermination.
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  • 6
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: A number of recent research works in lactic acid bacteria aim towards the design of new strains that could be used as live vectors for the delivery of antigens for oral vaccination, or other therapeutic molecules. In this work, an inducible expression system based on the Lactobacillus casei lactose operon promoter was used to express three important surface antigens of Streptococcus pneumoniae in this lactic acid bacterium: a virulence-related pneumococcal surface antigen (PsaA) and two variants of the virulence factor PspA (pneumococcal surface protein A). Expression of the three proteins was induced upon growth on lactose and strongly repressed by glucose. These proteins were produced intracellularly. Also, secretion to the growth medium was achieved by means of a fusion to the secreting and processing signals from the L. casei surface proteinase. Interestingly, while secreted PspA proteins were found in the culture supernatants, PsaA remained trapped in the cell wall. Expression of pneumococcal antigens in a food-grade organism opens an alternative for mucosal vaccination against this important pathogen.
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  • 7
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Lactobacillus sakei is one of the most important lactic acid bacteria of meat and fermented meat products. It is able to degrade arginine with ammonia and ATP production by the arginine deiminase pathway (ADI). This pathway is composed of three enzymes: arginine deiminase, ornithine transcarbamoylase and carbamate kinase, and an arginine transport system. The transcription of the ADI pathway is induced by arginine and subjected to catabolite repression. In order to understand the physiological role of the degradation of this amino acid we investigated the growth of bacteria under various conditions. We show that arginine degradation is responsible for an enhanced viability during the stationary phase when cells are grown under anaerobiosis. Arginine is necessary for the induction of the ADI pathway but in association with another environmental signal. Using a mutant of the L-lactate dehydrogenase unable to lower the pH we could clearly demonstrate that (i) low pH is not responsible for cell death during the stationary phase, so survival is due to another factor than elevated pH, (ii) neither low pH nor oxygen limitation is responsible for the induction of the ADI pathway together with arginine since the ldhL mutant is able to degrade arginine under aerobiosis.
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  • 8
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: We have cloned and sequenced the Lactobacillus casei ptsH and ptsI genes, which encode enzyme I and HPr, respectively, the general components of the phosphoenolpyruvate–carbohydrate phosphotransferase system (PTS). Northern blot analysis revealed that these two genes are organized in a single-transcriptional unit whose expression is partially induced. The PTS plays an important role in sugar transport in L. casei, as was confirmed by constructing enzyme I-deficient L. casei mutants, which were unable to ferment a large number of carbohydrates (fructose, mannose, mannitol, sorbose, sorbitol, amygdaline, arbutine, salicine, cellobiose, lactose, tagatose, trehalose and turanose). Phosphorylation of HPr at Ser-46 is assumed to be important for the regulation of sugar metabolism in Gram-positive bacteria. L. casei ptsH mutants were constructed in which phosphorylation of HPr at Ser-46 was either prevented or diminished (replacement of Ser-46 of HPr with Ala or Thr respectively). In a third mutant, Ile-47 of HPr was replaced with a threonine, which was assumed to reduce the affinity of P–Ser–HPr for its target protein CcpA. The ptsH mutants exhibited a less pronounced lag phase during diauxic growth in a mixture of glucose and lactose, two PTS sugars, and diauxie was abolished when cells were cultured in a mixture of glucose and the non-PTS sugars ribose or maltose. The ptsH mutants synthesizing Ser-46–Ala or Ile-47–Thr mutant HPr were partly or completely relieved from carbon catabolite repression (CCR), suggesting that the P–Ser–HPr/CcpA-mediated mechanism of CCR is common to most low G+C Gram-positive bacteria. In addition, in the three constructed ptsH mutants, glucose had lost its inhibitory effect on maltose transport, providing for the first time in vivo evidence that P–Ser–HPr participates also in inducer exclusion.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Molecular genetics and genomics 234 (1992), S. 401-411 
    ISSN: 1617-4623
    Keywords: Lactococcus protein export ; Expression signals ; Signal peptide ; α-amylase ; β-lactamase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Broad-host-range plasmids carrying α-amylase or β-lactamase reporter genes lacking a signal sequence were used to select export elements from Lactococcus lactis chromosomal DNA that could function as signal sequences. Fragments containing such elements were identified by their ability to direct the export of the reporter proteins in Escherichia coli. Several of the selected export elements were also active in Bacillus subtilis and L. lactis, although the efficiencies depended strongly on the host organism and reporter gene used. The export elements AL9 and BL1 were highly efficient in L. lactis in the expression and secretion of at least two heterologous proteins (Bacillus licheniformis α-amylase and E. coli TEM-β-lactamase). AL9 even permitted growth of this organism on starch as the sole carbon source. Nucleotide sequence analysis of five selected fragments indicated that these encode oligopeptides with the major characteristics of typical signal peptides. The putative expression signals had a limited similarity to previously described expression signals for E. coli, B. subtilis and L. lactis. Differences in both expression and export efficiency are likely to underlie the host-specific effects.
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  • 10
    Publication Date: 2010-02-24
    Print ISSN: 0175-7598
    Electronic ISSN: 1432-0614
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Published by Springer
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