Bacteria Streptococcus Thermophilus Research Articles

Characterization of the gor gene of the lactic acid bacterium Streptococcus thermophilus CNRZ368

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.

Basic features of the Streptococcus thermophilus heat shock response

The heat shock response was investigated in the thermophilic acid bacterium Streptococcus thermophilus. The heat resistance (58°C, 30 min) of log-phase cells grown at 42°C was enhanced by pretreatment at 52°C for 15 or 30 min. Concurrently to this acquired thermotolerance, two-dimensional gel electrophoresis indicates that the cells induced the synthesis of at least 22 heat shock proteins after temperature upshift. Furthermore, following SDS-PAGE, Western blotting, and immunological analysis, six proteins were found to be antigenically related to the Escherichia coli heat shock proteins DnaK, DnaJ, GroEL, GrpE, and La and to the Bacillus subtilis σ43 factor Among these six proteins, two related to DnaK and GroEL, are clearly overexpressed during this stress. It is concluded that S. thermophilus possesses a heat shock response similar to that known to occur in mesophilic microorganisms.

Molecular cloning and nucleotide sequencing of the aspartate racemase gene from lactic acid bacteria Streptococcus thermophilus

The gene coding aspartate racemase (EC 5.1.1.13) was cloned from the lactic acid bacteria Streptococcus thermophilus IAM10064 and expressed efficiently in Escherichia coli. The 2.1 kilobase pairs long full length clone had an open reading frame of 729 nucleotides coding for 243 amino acids. The calculated molecular weight of 27,945 agreed well with the apparent molecular weight of 28,000 found in sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis of the aspartate racemase purified from S. thermophilus. The N-terminal amino acid sequence from the purified protein exactly matches the derived sequence. In addition, the amino acid composition compiled from the derived sequence is very similar to that obtained from the purified recombinant protein. No significantly homologous proteins were found in a protein sequence data bank. Even the homology scores with alanine racemases of Salmonella typhimurium and Bacillus stearothermophilus were low. Aspartate racemase was overproduced in Escherichia coli NM522 with plasmid pAG6-2-7, which was constructed from two copies of the gene linked with a tac promoter and plasmid vector pUC18. The amount of aspartate racemase increases with the growth of E. coli and almost no degradation of the enzyme was observed. The maximum amount of the produced enzyme reached approx. 20% of the total protein of E. coli.

Safely teaching Koch's postulates on the causation of infectious disease

Koch's postulates are a set of criteria by which the causation of infectious disease can be systematically tested. They also provide a basis for understanding virulence and host-parasite interactions in disease. The postulates can be applied more generally to interactions between microbe and host (or habitat) to identify and define the impact of the microbe in the system. Yoghurt, a fermented milk product generated by the synergistic action of two species of bacteria (Streptococcus thermophilus and Lactobacillus bulgaricus), can be used to demonstrate an interaction between ‘parasite’ (bacteria) and ‘host’ (milk) leading to the ‘symptoms’ of ‘lactic acidosis’ of the milk. This interaction can be safely examined in a minimally equipped laboratory, and provides practice in manipulative and analytical skills in basic microbiology, in the planning of controlled experiments, and in the testing of models to account for the changes wrought on milk by the ‘infecting’ bacteria. In terms of conceptual level and inf...

Enhancement in cell mass concentration of lactic acid bacteria with fed-batch preculture technique.

Attempts were made with the lactic acid bacterium Streptococcus thermophilus on lactose medium to seek out the optimal cultivation condition to increase the cell mass concentration in batch cultures. The batch processing parameters involved were initial substrate concentration, inoculum size and cellular activities of inoculated cells. Change in cellular activities was adjusted with fed-batch preculture technique by regulating the feed rate per unit culture volume and the substrate concentration in the medium. Consequently, the highest cell mass concentration of 1.4 kg/m3 was attained with an inoculum from the preculture vessel of the dilution rate at 0.35h-1 and substrate concentration in the medium at 77 kg/m 3.

Growth of Thermoresistant Streptococci and Deposition of Milk Constituents on Plates of Heat Exchangers During Long Operating Times

Adhesion of the thermoresistant bacterium Streptococcus thermophilus to the surface of a heat exchanger and deposition of milk constituents during long operating times were investigated. Experiments were carried out on a pilot plant pasteurizer with raw whole and preheated skim milk. Adsorption of calcium, phosphorus and proteins was studied using chemical analysis, scanning electron microscopy and X-ray microanalysis. With increasing operating times the amount of deposits increased gradually on the raw milk side of the regenerative section and in the heating section, whereas on the pasteurized side of the regenerative section no detectable deposits were formed. The bacteria adhering to the plates of the heat exchanger were sampled with a swab technique. The bacteria adhered mainly to the plates in the pasteurized section. Electron micrographs of sample plates showed that the bacteria seemed to adhere directly to the metal surface, without calcium phosphate acting as an intermediary.