The consequence of COVID-19: how the United States moved from security provider to security consumer.

Deliberations over the COVID-19 pandemic's long-term effects on the global balance of power have spurred a large and rancorous debate, including speculation about a shift in the definition of national security and prescriptions about where it should focus. That argument will no doubt continue. But we argue that one consequence is already evident: the United States has spent the last seventy years portraying itself as a security provider in all key domains-for many an intrinsic component of its status as a global leader. One reasonable broad conclusion from the US struggle with COVID-19 is that it has further forfeited its broad leadership position on the basis of its behaviour. Yet that, although possibly true, would only portray one element of the story. The more profound insight exposed by COVID-19 is of a new reality: in a world where both naturogenic and anthropogenic threats pose immense national security challenges, decades of mistaken assumptions and policy choices have created a new environment, one where the United States has been redefined as a security consumer, at least in terms of international public health issues associated with the spread of deadly infectious diseases.

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).

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.

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.