Search PubMed⌕ Search

Biomedical subjects

Paul D Sniegowski

Publications and source records attributed to Paul D Sniegowski.

9 recordsLinked to original sources
PubMed2006

Mate choice assays and mating propensity differences in natural yeast populations.

In sexual microbes, mating occurs by fusion of individual cells. This complete fitness investment suggests that cell behaviour could potentially mediate prezygotic isolation between microbial species, a topic about which very little is known. To investigate this possibility, we conducted individual cell mate choice trials and mass-culture mating propensity assays with isolates from sympatric natural populations of the closely related yeasts Saccharomyces cerevisiae and Saccharomyces paradoxus. Although we found no evidence for active species recognition in mate choice, we observed a marked difference in mating propensity between these two species. We briefly discuss the possibility that this mating propensity difference may contribute to reproductive isolation between S. cerevisiae and S. paradoxus in nature.

Reproduction↗
PubMed2006

Evolvability.

Explore the source record for details and available documents.

Adaptation, Biological↗
PubMed2004

Population genetic variation in gene expression is associated with phenotypic variation in Saccharomyces cerevisiae.

BACKGROUND: The relationship between genetic variation in gene expression and phenotypic variation observable in nature is not well understood. Identifying how many phenotypes are associated with differences in gene expression and how many gene-expression differences are associated with a phenotype is important to understanding the molecular basis and evolution of complex traits. RESULTS: We compared levels of gene expression among nine natural isolates of Saccharomyces cerevisiae grown either in the presence or absence of copper sulfate. Of the nine strains, two show a reduced growth rate and two others are rust colored in the presence of copper sulfate. We identified 633 genes that show significant differences in expression among strains. Of these genes, 20 were correlated with resistance to copper sulfate and 24 were correlated with rust coloration. The function of these genes in combination with their expression pattern suggests the presence of both correlative and causative expression differences. But the majority of differentially expressed genes were not correlated with either phenotype and showed the same expression pattern both in the presence and absence of copper sulfate. To determine whether these expression differences may contribute to phenotypic variation under other environmental conditions, we examined one phenotype, freeze tolerance, predicted by the differential expression of the aquaporin gene AQY2. We found freeze tolerance is associated with the expression of AQY2. CONCLUSIONS: Gene expression differences provide substantial insight into the molecular basis of naturally occurring traits and can be used to predict environment dependent phenotypic variation.

Color↗
PubMed2004

Sympatric natural Saccharomyces cerevisiae and S. paradoxus populations have different thermal growth profiles.

Saccharomyces cerevisiae and its close congener S. paradoxus are typically indistinguishable by the phenotypic criteria of classical yeast taxonomy, but they are evolutionarily distinct as indicated by hybrid spore inviability and genomic sequence divergence. Previous work has shown that these two species coexist in oak-associated microhabitats at natural woodland sites in North America. Here, we show that sympatric populations of S. cerevisiae and S. paradoxus from a single natural site are phenotypically differentiated in their growth rate responses to temperature. Our main finding is that the S. cerevisiae population exhibits a markedly higher growth rate at 37 degrees C than the S. paradoxus population; we also find possible differences in growth rate between these populations at two lower temperatures. We discuss the implications of our results for the coexistence of these yeasts in natural environments, and we suggest that thermal growth response may be an evolutionarily labile feature of these organisms that could be analyzed using genomic approaches.

Acclimatization↗
PubMed2003

Distribution and sequence analysis of a novel Ty3-like element in natural Saccharomyces paradoxus isolates.

Little is known about the transposable elements of species closely related to Saccharomyces cerevisiae. We present a novel transposable element in Saccharomyces paradoxus, a close congener of S. cerevisiae. Sequence analysis of this element, designated Ty3-1p, indicates that it is a homologue of the S. cerevisiae Ty3 element. Ty3-1p shares 82% nucleotide identity with an S. cerevisiae Ty3 element and appears to be structured identically to Ty3, containing two overlapping open reading frames, six retroviral-like domains, a J domain, and flanking sigma-like elements. A sigma element from Ty3-1p is 75% identical to a Ty3 sigma element. There is no evidence of horizontal transfer of Ty3 in Saccharomyces sensu stricto. We assess the distributions of Ty3p and Ty3 element insertions in natural population samples of S. paradoxus and S. cerevisiae. The S. paradoxus population sample exhibits Ty3p insertions present at a variety of sites at low frequency; this suggests that Ty3p elements are active in the sampled population. The S. cerevisiae population sample exhibits a uniform Ty3 hybridization profile in which all element insertions appear to be fixed. We comment on the possible causes of these contrasting observed distributions (GenBank Accession Nos AY198186 and AY198187).

Amino Acid Sequence↗
PubMed2003

Spontaneously arising mutL mutators in evolving Escherichia coli populations are the result of changes in repeat length.

Over the course of thousands of generations of growth in a glucose-limited environment, 3 of 12 experimental populations of Escherichia coli spontaneously and independently evolved greatly increased mutation rates. In two of the populations, the mutations responsible for this increased mutation rate lie in the same region of the mismatch repair gene mutL. In this region, a 6-bp repeat is present in three copies in the gene of the wild-type ancestor of the experimental populations but is present in four copies in one of the experimental populations and two copies in the other. These in-frame mutations either add or delete the amino acid sequence LA in the MutL protein. We determined that the replacement of the wild-type sequence with either of these mutations was sufficient to increase the mutation rate of the wild-type strain to a level comparable to that of the mutator strains. Complementation of strains bearing the mutator mutations with wild-type copies of either mutL or the mismatch repair gene uvrD rescued the wild-type mutation rate. The position of the mutator mutations-in the region of MutL known as the ATP lid-suggests a possible deficiency in MutL's ATPase activity as the cause of the mutator phenotype. The similarity of the two mutator mutations (despite the independent evolutionary histories of the populations that gave rise to them) leads to a discussion of the potential adaptive role of DNA repeats.

Adenosine Triphosphatases↗
PubMed2002

Fitness evolution and the rise of mutator alleles in experimental Escherichia coli populations.

We studied the evolution of high mutation rates and the evolution of fitness in three experimental populations of Escherichia coli adapting to a glucose-limited environment. We identified the mutations responsible for the high mutation rates and show that their rate of substitution in all three populations was too rapid to be accounted for simply by genetic drift. In two of the populations, large gains in fitness relative to the ancestor occurred as the mutator alleles rose to fixation, strongly supporting the conclusion that mutator alleles fixed by hitchhiking with beneficial mutations at other loci. In one population, no significant gain in fitness relative to the ancestor occurred in the population as a whole while the mutator allele rose to fixation, but a substantial and significant gain in fitness occurred in the mutator subpopulation as the mutator neared fixation. The spread of the mutator allele from rarity to fixation took >1000 generations in each population. We show that simultaneous adaptive gains in both the mutator and wild-type subpopulations (clonal interference) retarded the mutator fixation in at least one of the populations. We found little evidence that the evolution of high mutation rates accelerated adaptation in these populations.

Adenosine Triphosphatases↗
PubMed2002

Saccharomyces cerevisiae and Saccharomyces paradoxus coexist in a natural woodland site in North America and display different levels of reproductive isolation from European conspecifics.

We report the isolation of multiple strains of Saccharomyces cerevisiae and Saccharomyces paradoxus from a natural woodland site in southeastern Pennsylvania, USA, using enrichment culturing in a medium containing 7.6% (v/v) ethanol. The method was applied to bark and flux material collected from broad-leaved trees (mostly Quercus spp.) and to associated soils. Many candidate wild strains of Saccharomyces were isolated using this method, most of them from soils associated with oaks. Matings to genetically marked tester strains of S. cerevisiae and S. paradoxus identified roughly equal numbers of these two species within this collection. The S. paradoxus isolates showed significant partial reproductive isolation from a conspecific European strain, whereas the S. cerevisiae isolates did not. Variability in both chromosome size and Ty1 element hybridization profiles was observed within both populations at this site. We discuss the relevance of our data to current debates concerning whether S. cerevisiae is a wild species or a domesticated species.

Culture Media↗