Biomedical subjects

A Hartke

Publications and source records attributed to A Hartke.

26 records · Page 2Linked to original sources

PubMed1996

The Lactic Acid Stress Response of Lactococcus lactis subsp. lactis

The lactic acid tolerance response (LATR) of the lactic acid bacterium Lactococcus lactis subsp. lactis has been studied. A dramatic increase in survival to a severe acid stress (pH 3.9) was obtained by preexposing the cells for 30 min to a mildly acid shock at pH 5.5. Whole-cell protein extract analysis revealed that during the acid tolerance response 33 polypeptides are induced over the level of naive cells. Among these are the major heat shock proteins DnaK and GroEL. In conjunction with a previous report (Hartke et al. 1994), the results establish that L. lactis can adapt to lactic acid exposure in two different ways: a logarithmic phase LATR, which may be activated by protons, and a stationary-phase LATR, which needs no activation by protons. Both systems are independent of de novo protein synthesis.

Journal Article↗

PubMed1995

Induction of thermotolerance by chemical agents in Lactococcus lactis subsp. lactis IL1403.

Like in other organisms tested to date, adapted cells of Lactococcus lactis subsp. lactis IL1403 pretreated at 42 degrees C for 30 min develop a thermotolerant state, i.e. an increased ability to survive subsequent exposure to a lethal challenge temperature (52 degrees C for 15 or 30 min). In different cellular systems, chemicals as diverse as divalent metal salts, natural or synthetic compounds trigger the development of thermotolerance. Yet, in L. lactis subsp. lactis IL1403, among the 17 chemicals tested, only four induced this transient increased tolerance to heat: cadmium chloride, mercury chloride, sodium azide and beta-mercaptoethanol. Intriguingly, none of these four compounds induced the synthesis of three major heat shock proteins (DnaK, GroEL and hsp104-analogue), which are believed to be responsible for thermotolerance in most organisms. It is suggested that: (i) the lesions produced by these various 'proteotoxic' agents are fundamentally different from those produced by heat; (ii) heat shock protein synthesis and transient induced tolerance to heat are not tightly correlated phenomena in L. lactis subsp. lactis as they are in Escherichia coli and some other organisms.

Adaptation, Physiological↗

PubMed1994

Starvation-Induced Stress Resistance in Lactococcus lactis subsp. lactis IL1403.

Carbohydrate-starved cultures of Lactococcus lactis subsp. lactis IL1403 showed enhanced resistance to heat, ethanol, acid, osmotic, and oxidative stresses. This cross-protection seems to be established progressively during the transitional growth phase, with maximum resistance occurring when cells enter the stationary phase. Chloramphenicol or rifamycin treatment does not abolish the development of a tolerant cell state but, on the contrary, seems to provoke this response in L. lactis subsp. lactis.

Journal Article↗

PubMed1993

Nucleotide sequence of the Lactococcus lactis NCDO 763 (ML3) rpoD gene.

The complete nucleotide sequence of rpoD gene from Lactococcus lactis has been determined. The nucleotide data have indicated the presence of an open reading frame of 1020 base pairs encoding a polypeptide which shares the framework structure for principal sigma factors of eubacteria strains.

Amino Acid Sequence↗

PubMed1993

Characterization of the heat shock response in Enterococcus faecalis.

We have characterized the general properties of the heat shock response of the Gram-positive hardy bacterium Enterococcus faecalis. The heat resistance (60 degrees C or 62.5 degrees C, 30 min) of log phase cells of E. faecalis grown at 37 degrees C was enhanced by exposing cells to a prior heat shock at 45 degrees C or 50 degrees C for 30 min. These conditioning temperatures also induced ethanol (22%, v/v) tolerance. The onset of thermotolerance was accompanied by the synthesis of a number of heat shock proteins. The most prominent bands had molecular weights in the range of 48 to 94kDa. By Western blot analysis two of them were found to be immunologically related to the well known DnaK (72kDa) and GroEL (63kDa) heat shock proteins of Escherichia coli. Four other proteins showing little or no variations after exposure to heat are related to DnaJ, GrpE and Lon (La) E. coli proteins and to the Bacillus subtilis sigma 43 factor. Ethanol (2% or 4%, v/v) treatments elicited a similar response although there was a weaker induction of heat shock proteins than with heat shock.

Antigens, Bacterial↗

PubMed1993

Partial characterization of an rpoD-like gene of Lactococcus lactis subsp. lactis ML3 with a polymerase chain reaction-based approach.

With degenerated oligonucleotide primers for conserved regions of bacterial sigma factor proteins, a 117-bp internal DNA fragment of an rpoD-like gene of Lactococcus lactis subsp. lactis ML3 was amplified by the polymerase chain reaction (PCR). The DNA sequence of this PCR product was determined by cycle sequencing, and the deduced amino acid sequence of this internal fragment showed an extensive homology with the known sigma factor sequences from six other microorganisms and present a 13-amino acid region corresponding to the typical "RpoD box" of primary sigma factors. This PCR product was used as a probe to specifically detect sigma homologs in Pediococcus acidilactici, Leuconostoc lactis, Lactobacillus helveticus, Lactobacillus acidophilus, Enterococcus faecalis, Streptococcus thermophilus, and Lactococcus lactis subsp. cremoris. These data are consistent with the existence of a high similarity between the primary sigma factors from diverse Gram-positive microorganisms.

Amino Acid Sequence↗

PubMed1992

Is thermotolerance correlated to heat-shock protein synthesis in Lactococcus lactis subsp. lactis?

Exposure of Lactococcus lactis subsp. lactis cells to a heat shock at 40 degrees C for 30 min induces thermotolerance, the increased ability of bacterial cells to survive exposure to lethal temperature (52 degrees C for 25 min). This transient state of thermal resistance is accompanied, as in Escherichia coli, by the synthesis of a new set of specific proteins termed heat-shock proteins (Hsps). Pre-treatment of the bacterial cells by antibiotics (streptomycin, spiramycin, kanamycin and erythromycin) known to act on translation, induces the major Hsps synthesis but no thermal protection; conversely, puromycin and amino acid analogues treatments, known to produce abnormal and incomplete peptides, triggers the thermotolerance state without inducing significant Hsps synthesis. These results demonstrate that heat-shock response and induced thermotolerance are not tightly correlated phenomena in L. lactis subsp. lactis.

Adaptation, Physiological↗

PubMed1991

Survival of M13mp18 gapped duplex DNA as a function of gap length.

Gaps of various lengths were generated in duplex M13mp18DNA by exonuclease III digestion of nicked DNA. The length of the gap increased essentially linearly with time of digestion. Survival in E. coli, however, was not a linear function of gap length. Similar results were obtained when gaps were produced by stopping the polymerization reaction. The survival (N/No) of the gapped DNA in SOS-induced E. coli cells transformed by electroporation and uninduced cells transformed by the calcium chloride method can be quantitatively accounted for by a kinetic model assuming a single-strand endonucleolytic activity (Pd) in the cell which increases linearly with gap length (L) and a repair activity by a polymerase (Pr) which is independent of gap length (formula 1). With uninduced cells transformed by electroporation the results can be mathematically described if assumptions are made concerning the protection of single-stranded parts of the DNA by single-strand affinic proteins.

Base Sequence↗