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Biomedical subjects

J E Beringer

Publications and source records attributed to J E Beringer.

At least 19 recordsLinked to original sources
PubMed2000

The purMN genes of Rhizobium leguminosarum and a superficial link with siderophore production.

We isolated a mutant of R. leguminosarum initially on the basis of reduced production of the siderophore vicibactin on chrome azurol sulfonate (CAS)/agar indicator plates. The mutation was in the purMN operon and the mutant was shown to be an adenine auxotroph and defective for nodulation of peas. The siderophore defect appears to be trivial, being due to diminished growth of the auxotroph on agar-based minimal medium, which contains unknown contaminant(s) that allow it grow poorly. Transcriptional fusions showed that purMN was transcribed at relatively high levels in media containing purines. Expression was enhanced, approximately twofold, if purines were omitted.

Escherichia coli↗
PubMed2000

Is there a future for GMOs?

Despite strict regulation and a clean safety record, research and development of genetically modified (GM) crops and other organisms has been confronted with tremendous public hostility. Why has this happened, and how can scientists try to guide the debate into more rational channels? The answers may determine the future of GM technology and our ability to provide for a growing world population.

Biotechnology↗
PubMed1999

Molecular evidence for shifts in polysaccharide composition associated with adaptation of soybean Bradyrhizobium strains to the Brazilian Cerrado soils.

Pyrolysis mass spectrometry (PyMS) and DNA fingerprinting (RAPD and RSalpha hybridization) were used to characterize soybean inoculant strains and root nodule isolates of bradyrhizobia from the Brazilian Cerrado soils. Most isolates were shown to be derived from the inoculant strains on the basis of genotype comparisons by DNA fingerprinting. Phenotypic analysis (using PyMS) of the strains and separately of the polysaccharides derived from them showed that the nodule isolates differed from the parental strains, suggesting adaptation to the Cerrado soil environment. The extent of the differences between the derivatives and inoculant strains was similar for comparisons made on the basis of whole-cell preparations or from the isolated polysaccharides, indicating that the adaptation was caused by changes in the composition of the polysaccharides produced.

Adaptation, Physiological↗
PubMed1997

Molecular detection of streptomycin-producing streptomycetes in Brazilian soils.

Actinomycetes were isolated from soybean rhizosphere soil collected as two field sites in Brazil. All the isolates were identified as Streptomyces species and were screened for streptomycin production and the presence of two genes, strA and strB1, known to be involved in streptomycin biosynthesis in Streptomyces griseus. Antibiotic resistance profiles were determined for 53 isolates from cultivated and uncultivated sites, and approximately half the strains were streptomycin resistance. Clustering by the unweighted pair group method with averages indicated the presence of two major clusters, with the majority of resistant strains from cultivated sites being placed in cluster 1. Only representatives from this cluster contained strA. Streptomycetes containing strA and strB1 were phenotypically diverse, and only half could be assigned to known species. Sequence comparison of 16S rRNA and trpBA (tryptophan synthetase) genes revealed that streptomycin- producing streptomycetes were phylogenetically diverse. It appeared that a population of streptomycetes had colonized the rhizosphere and that a proportion of these were capable of streptomycin production.

Amino Acid Sequence↗
PubMed1993

The survival of bacteria exposed to desiccation on surfaces associated with farm buildings.

The survival of 11 species of Gram-negative and Gram-positive bacteria was examined on different surfaces exposed to desiccation. There were large variations between species; Pseudomonas spp. and Rhizobium leguminosarum biovars survived for less than 2 d, whilst Enterococcus spp. survived for more than 11 weeks. The type of surface on to which the bacteria were deposited affected survival, but with different effects between species. In addition the survival of spontaneous nalidixic acid-resistant (Nal-r) mutants of a natural Escherichia coli isolate were compared. Overall the differences were slight, but of seven resistant mutants, five survived better than the parent whilst one survived less well. Nine transposon insertion derivatives of one of the Nal-r mutants (ECO80) which survived better than the parent were compared; all survived similarly to the parent except ECO883 which survived less well. The growth characteristics of ECO883 and ECO80 were compared; at high osmotic pressures (> 0.4 mol 1-1 NaCl) ECO883 grew more slowly and showed a longer lag time than the parent. Of the osmoregulatory functions studied, ECO883 appeared to be altered with respect to K+ transport or accumulation, although the transposon insertion had occurred in a gene distant from known K+ transport genes.

Agriculture↗
PubMed1993

The effect of colony age on PCR fingerprinting.

The pattern of DNA fragments produced by the polymerase chain reaction using arbitrary primers is strongly influenced by the age of the colonies sampled. We show that the number, clarity and reproducibility of the bands produced is optimal when very young colonies are sampled.

Bacteria↗
PubMed1992

Differential in vitro inhibition of feline enteric coronavirus and feline infectious peritonitis virus by actinomycin D.

The growth of feline enteric coronavirus strain 79-1683 in whole feline embryo cells was inhibited by the presence of 1 microgram/ml of actinomycin D in the culture fluid. No virus-specific mRNAs could be detected in such cultures and yields of infectious virus were depressed by > 99%. By contrast, the antigenically related feline infectious peritonitis virus strain 79-1146 was unaffected by the presence of actinomycin D, indicating a fundamental difference between the two feline coronavirus strains in their requirements for host-encoded function(s).

Animals↗
PubMed1988

Melanin production by Rhizobium strains.

Different Rhizobium and Bradyrhizobium strains were screened for their ability to produce melanin. Pigment producers (Mel) were found among strains of R. leguminosarum biovars viceae, trifolii, and phaseoli, R. meliloti, and R. fredii; none of 19 Bradyrhizobium strains examined gave a positive response. Melanin production and nod genes were plasmid borne in R. leguminosarum biovar trifolii RS24. In R. leguminosarum biovar phaseoli CFN42 and R. meliloti GR015, mel genes were located in the respective symbiotic plasmids. In R. fredii USDA 205, melanin production correlated with the presence of its smallest indigenous plasmid.

Journal Article↗
PubMed1984

A physical map of pPH1JI and pJB4JI.

The antibiotic resistance plasmid pPH1JI was derived from two IncP plasmids, R751 and R1033. The suicide vector for Tn5, pJB4JI, contains pPH1JI, bacteriophage Mu, and Tn5. Restriction enzyme cleavage maps for pPH1JI and pJB4JI, and the antibiotic resistance levels determined by pPH1JI and its parent plasmids are presented. The relationships between pPH1JI and its parent plasmids, and pJB4JI, are discussed.

Chromosome Mapping↗
PubMed1982

Molecular cloning of Rhizobium trifolii genes involved in symbiotic nitrogen fixation.

DNA sequences responsible for the development and maintenance of symbiotic nitrogen fixation have been identified and isolated from Rhizobium trifolii. Symbiotically-defective strains were generated by random mutagenesis with the transposon Tn5. The defective genes which give rise to the mutant phenotype have been cloned into bacterial plasmids and used as hybridization probes to isolate the corresponding wild-type genes from a clone bank of R. trifolii DNA. Symbiotic genes cloned in this manner are able to correct the lesion caused by the insertion of the transposon in their respective mutants and so restore the nitrogen fixation phenotype. The correction of the mutation is shown to occur by two distinguishable mechanisms--either by complementation or by homologous recombination. This approach provides a reliable method for isolation and mapping of bacterial DNA sequences involved in symbiotic nitrogen fixation.

Cloning, Molecular↗
PubMed1979

The Rhizobium--legume symbiosis.

The rhizobia are soil microorganisms that can interact with leguminous plants to form root nodules within which conditions are favourable for bacterial nitrogen fixation. Legumes allow the development of very large rhizobial populations in the vicinity of their roots. Infections and nodule formation require the specific recognition of host and Rhizobium, probably mediated by plant lectins. Penetration of the host by a compatible Rhizobium species usually provokes host root cell division to form the nodule, and a process of differentiation by both partners then ensues. In most cases the rhizobia alter morphologically to form bacteroids, which are usually larger than the free-living bacteria and have altered cell walls. At all stages during infection, the bacteria are bounded by host cell plasmalemma. The enzyme nitrogenase is synthesized by the bacteria and, if leghaemoglobin is present, nitrogen fixation will occur. Leghaemoglobin is a product of the symbiotic interaction, since the globin is produced by the plant while the haem is synthesized by the bacteria. In the intracellular habitat the bacteria are dependent upon the plant for supplies of energy and the bacteroids, in particular, appear to differentiate so that they are no longer able to utilize the nitrogen that they fix. Regulation of the supply of carbohydrate and the use of the fixed nitrogen thus appear to be largely governed by the host.

Leghemoglobin↗
PubMed1978

Tryptophan genes in Rhizobium--their organization and their transfer to other bacterial genera.

R. leguminosarum trp alleles mapped by R68.45-mediated recombination were located in three distinct chromosomal regions. We isolated three derivatives of R68.45 that carried different trp genes of R. meliloti. Each of the plasmids suppressed all of the R. leguminosarum trp alleles in a particular region. The R-primes were transferred to strains of P. aeruginosa carrying mutations in different trp genes. The plasmid pAJ24JI suppressed trpA, B and F mutants, pAJ73JI suppressed trpC and D and pAJ88JI suppressed a trpE mutant. When the R-primes were transferred to E. coli trp strains they failed to suppress any trp mutants. A derivative of pAJ24JI was isolated which was able to suppress trpA and F mutants of E. coli.

Escherichia coli↗
PubMed1976

Properties of plasmids constructed by the in vitro insertion of DNA from Rhizobium leguminosarum or Proteus mirabilis into RP4.

Plasmids have been constructed by insertion of DNA from Rhizobium leguminosarum or Proteus mirabilis into RP4 (an R factor of group P). Such recombinant plasmids retain the wide host range of the parental plasmid, being as efficiently transmissible as the unmodified RP4 and are stably maintained in rapidly growing cultures. The recombinant plasmids, even though each contained a DNA sequence absolutely identical with that of the host strain, are no more efficient at mobilizing the transfer of chromosomal genetic information from that host strain than was unmodified RP4. We therefore conclude that an unknown factor must be essential in the process of chromosome mobilization and rate limiting for that process.

Ampicillin↗
PubMed1975

Identification of the rhizobium strains in pea root nodules using genetic markers.

Pea plants were inoculated jointly with pairs of genetically marked strains of Rhizobium leguminosarum. Out of 297 modules examined 56 contained both inoculant strains. The ratios of the strains in the inoculum did not affect the frequencies of mixed nodules. Generally one of the strains consistently occupied the majority of the nodules and ithe mixed nodules comprised the majority of bacteria. Transfer of the P-group R factor, RP4, between certain strains of Rhizobium within mixed nodules was detected. In some cases the non-parental progeny comprised 10% of the rhizobia isolated from such nodules.

Acetylene↗