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Biomedical subjects

D Dykhuizen

Publications and source records attributed to D Dykhuizen.

13 recordsLinked to original sources
PubMed2001

Distinct levels of genetic diversity of Borrelia burgdorferi are associated with different aspects of pathogenicity.

Different species of pathogenic Borrelia show different symptoms and tick vector specificity. Even within regions where only one species is found, Lyme disease progresses very differently from one patient to another. Since Borrelia shows very little recombination either within or between species, alleles of a gene can be used to mark clones. The ospC gene is highly variable within each species and can be used to define groups of related clones. It has been previously shown that only four out of seventeen ospC groups of Borrelia burgdorferi sensu stricto cause invasive forms of the disease. Other groups cause erythema migrans, a skin rash at the site of the tick bite, but not invasive disease, while still other groups seem to be nonpathogenic to humans. In this study we extend the analysis of the ospC gene to the other pathogenic species, Borrelia garinii and Borrelia afzelii. Only two groups in B. afzelii and four groups in B. garinii cause invasive disease. Thus, only ten out of the 58 defined ospC groups cause invasive and presumably chronic Lyme disease.

Animals↗
PubMed1998

Culture-confirmed reinfection of a person with different strains of Borrelia burgdorferi sensu stricto.

In recent years, the utility of serum-based diagnostic testing for Lyme disease has improved substantially; however, recovery by culture of the bacterium from skin biopsies of suspected patients is still the only definitive laboratory test. Reinfection of patients has been assumed to occur but as yet has not been documented by serial isolates from the same person. We present a case of culture-confirmed reinfection of a patient in Menominee County, Michigan. Borrelia burgdorferi was isolated from the skin punch biopsy specimens during each episode of erythema migrans (EM) and was subjected to molecular strain typing, genetic analysis of two outer surface protein genes, protein profile analysis, and serum antibody response testing. Results show that these isolates are distinct strains of the bacterium and that the two episodes of EM were caused by independent infections. This report describes the documented, culture-confirmed reinfection of a human by two different strains of B. burgdorferi.

Antibodies, Bacterial↗
PubMed1995

Identification of an immunologically important hypervariable domain of major outer surface protein A of Borrelia burgdorferi.

The gene for the major outer surface protein A (OspA) from several clinically obtained strains of Borrelia burgdorferi, the cause of Lyme disease, has been cloned, sequenced, and expressed in Escherichia coli by using a T7-based expression system (J. J. Dunn, B. N. Lade, and A. G. Barbour, Protein Expr. Purif. 1:159-168, 1990). All of the OspAs have a single conserved tryptophan at residue 216 or, in some cases, 217; however, the region of the protein flanking the tryptophan is hypervariable, as determined by a moving-window population analysis of ospA from 15 European and North American isolates of B. burgdorferi. Epitope-mapping studies using chemically cleaved OspA and a TrpE-OspA fusion have indicated that this hypervariable region is important for immune recognition. Biophysical analysis, including fluorescence and circular dichroism spectroscopy, have indicated that the conserved tryptophan is buried in a hydrophobic environment. Polar amino acid side chains flanking the tryptophan are likely to be exposed to the hydrophilic solvent. The hypervariability of these solvent-exposed amino acid residues may contribute to the antigenic variation in OspA. To test this, we have performed site-directed mutagenesis to replace some of the potentially exposed amino acid side chains in the B31 protein with the analogous residues of a Borrelia garinii strain, K48. The altered proteins were then analyzed by Western blot (immunoblot) with monoclonal antibodies which bind OspA on the surface of the intact B31 spirochete. Our results indicate that specific amino acid changes near the tryptophan can abolish the reactivity of OspA to these monoclonal antibodies, which is an important consideration in the design of vaccines based on recombinant OspA.

Amino Acid Sequence↗
PubMed1980

Selective neutrality of 6PGD allozymes in E. coli and the effects of genetic background.

We have used gluconate-limited chemostats to study selective differences between isogenic strains of Escherichia coli K12 into which four naturally occurring alleles coding for allozymes of 6-phosphogluconate dehydrogenase (6PGD) had been transferred. The limit of detectability of selection with our procedures is a selection coefficient of 0.5%. In the normal E. coli K12 genetic background, all alleles are selectively neutral or nearly neutral. The absence of detectable selection does, however, depend on genetic background and on such environmental factors as cell density. In a genetic background containing a mutation that cuts off the alternative metabolic route for 6-phosphogluconate, selection between allozymes can be detected, and the selection is in the direction expected from the measured apparent Km values of the allozymes. Even when the alternative metabolic route is not blocked by mutation, one of the 6PGD allozymes has a detrimental, but density-dependent, interaction with a mutation conferring resistance to bacteriophage T5. In all cases, the observed selection is due to the allozymes themselves (or to associated regulatory elements), as the selection disappears when the chemostats are limited by a different carbon source (ribose plus succinate). Nevertheless, the four alleles do seem to be selectively neutral or nearly neutral in the normal E. coli K12 genetic background. Moreover, the distribution of allele frequencies in natural populations of E. coli is in accord with the expectations of selective neutrality.

Alleles↗
PubMed1978

Transport by the lactose permease of Escherichia coli as the basis of lactose killing.

Lactose killing is a peculiar phenomenon in which 80 to 98% of the Escherichia coli cells taken from a lactose-limited chemostat die when plated on standard lactose minimal media. This unique form of suicide is caused by the action of the lactose permease. Since uptake of either lactose or galactose by the lactose permease caused death, the action of rapid transport across the membrane must be the cause of the phenomenon. Alternative causes of lactose killing, such as accumulation of toxic metabolic intermediates or action of the beta-galactosidase, have been eliminated. It is proposed that rapid uptake of sugars by the lactose permease disrupts membrane function, perhaps causing collapse of the membrane potential.

Biological Transport↗
PubMed1978

The influences of a lambda prophage on the growth rate of Escherichia coli.

A lambda prophage increases the competitive ability of E. coli K12 in a glucose-limited chemostat. This phenomenon does not involve the lambdarex gene. Expression of the lambdarex gene conditionally decreases fitness in two ways: (1) it causes malT- but not malT+ lysogens to be at a selective disadvantage in competition with non-lysogens. (2) During adaptation to slow, glucose-limited chemostat growth from rapid, glucose-excess flask growth, expression of the lambdarex gene transiently decreases the growth rate when compared to the non-lysogen.

Bacteriophage lambda↗
PubMed1973

Genetic analysis of the system that reduces biotin-d-sulfoxide in Escherichia coli.

Four genes of Escherichia coli whose products are needed to reduce biotin-d-sulfoxide to biotin have been mapped: bisA next to chlA, bisB next to chlE, bisC linked to xyl, and bisD next to chlG. A defective lambda transducing phage, lambdadbis5, which carries all the bacterial genes between the lambda attachment site and chlE, was isolated and shown to have lost the phage genes from int through Q.

Biotin↗
PubMed1972

Conditional lethality of deletions which include uvrB in strains of Escherichia coli lacking deoxyribonucleic acid polymerase I.

Deletions of the uvrB gene were not obtained in polA1 strains of Escherichia coli either by selecting for spontaneous deletions or by transduction from strains carrying such deletions. A strain forming a temperature-sensitive deoxyribonucleic acid polymerase I and carrying a deletion of the uvrB gene is inviable at the nonpermissive temperature.

Cell Survival↗