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PubMed2002

Microbial population genomics and ecology.

The origins of biological complexity in microbial ecosystems are encoded within the collective genomes of the community. Cultivation-independent genomic studies provide direct access to the genomes of naturally occurring microbes, cultivated or not. Genome-enabled approaches are now significantly advancing current knowledge of genome content, diversity, population biology and evolution in natural microbial populations.

Ecology↗
PubMed1971

High dihydrofolate reductase levels in Diplococcus pneumoniae after mutation in the structural gene: biochemical and immunological evidence for increased synthesis.

A unique class of missense mutations in the dihydrofolate reductase structural gene of Diplococcus pneumoniae determines marked increases in the corresponding enzyme activity. Immunological evidence, based on precipitating and neutralizing antibody reactions, is presented in support of previously derived findings which attribute this increase in activity to an increase in the amount of enzyme protein. Biochemical evidence was obtained which shows that the increased amounts of dihydrofolate reductase protein in the mutants not owing to a decrease in degradation, reducing turnover, or to an increase in stability, and, therefore, probably related to an increase in the rate of synthesis of new protein. The manner in which a missense alteration of a structural gene might quantitatively alter the expression of that gene is discussed.

Animals↗
PubMed2026

Diet change reveals asymmetric response in gene expression and microbial composition across the digestive tract of two closely related herbivores.

BACKGROUND: Understanding what shapes variation in organisms' capacity to utilize novel resources is essential to predicting how species will respond to environmental change. For herbivores, exposure to toxic phytochemicals in novel plants may limit persistence in new habitats. We investigated the behavioral, physiological, genetic, and microbial consequences of diet switching in two closely related species of rodent herbivores that each consume differentially toxic plants in their native habitat, and that maintain different dietary strategies (i.e., relative dietary specialist versus relative generalist). RESULTS: In reciprocal laboratory feeding trials, we exposed wild-caught woodrats (genus Neotoma) to toxins characteristic of either familiar or novel plant secondary compounds. We measured changes in food and water intake, locomotor activity, gut microbial composition, and gene expression across the digestive tract following feeding trials. The dietary generalist responded minimally, but the specialist responded strongly when exposed to the novel diet. This response included behavioral and genetic components including increased water intake, reduction in locomotor activity, increased differential expression of detoxification genes, and a greater shift in gut microbial composition. CONCLUSIONS: The dietary specialist exhibited a strong response to diet switching that corresponded with ecologically relevant shifts in behavior and physiology that would have negative fitness consequences. Although the dietary specialist had a strong genetic and microbial response to novel plant secondary compounds, this response would likely be insufficient to overcome the immediate challenge of exposure to novel dietary toxins in the wild. Our results underscore the link between feeding strategy and the capacity to shift to novel dietary resources in response to environmental change.

Animals↗
PubMed1971

New regulatory mutation affecting some of the tryptophan genes in Pseudomonas putida.

Three indole analogues, 5-methylindole, 5-fluoroindole, and 7-methylindole, and the tryptophan analogue 5-fluorotryptophan were found to inhibit the growth of wild-type Pseudomonas putida. Mutants resistant to these analogues were obtained. Some of the 5-fluoroindole- and 5-fluorotryptophan-resistant strains exhibit an abnormality in the regulation of certain trp genes. These strains excrete anthranilate when grown in minimal medium in the presence or absence of the inhibitor. In these strains, the trpA, B, and D gene products, the first, second, and fourth enzymes of the tryptophan pathway, are produced in 20-fold excess over the normal wild-type level. The other enzymes of the pathway are unaffected. Exogenous tryptophan is still able to repress the expression of the trpABD cluster somewhat. Similarity between the 5-fluoroindole- and 5-fluorotryptophan-resistant strains suggests that the former compound becomes effective through conversion to the latter. Repression and derepression experiments with two anthranilate-excreting, 5-fluoroindole-resistant strains showed coordinate variation of the affected enzymes. The locus conferring resistance and excretion is not linked by transduction to any of the trp genes.

Chromatography, Paper↗
PubMed1975

Transfection with heteroduplex SPP1 DNA: a pyrimidine dimer induced influence on the conversion pattern.

Bacillus subtilis competent cells were transfected with SPP1 heteroduplices having pyrimidine dimers in one of the strands. The data obtained reveal that excision repair of the pyrimidine dimers influences the ratio of wild type versus mutant progeny observed in "normal" heteroduplex transfection. With increased exposure of one strand to UV dose the percentage of infective centers having the unirradiated strand genotype shows an increase. A comparison of the transfection data in her+ and her- host excludes asymmetric replication as the cause of the observed changes in the conversion pattern. The data can be explained on the basis of a dimer induced co-excision of the mismatched region. In addition transfection data from wild type/deletion mutant heteroduplices where the strand of mutant origin was irradiated exclude the possibility of the wild type loop being excised during uptake.

Bacillus subtilis↗