Xer Recombinase and Genome Integrity in Helicobacter pylori, a Pathogen without Topoisomerase IV

In the model organism E. coli, recombination mediated by the related XerC and XerD recombinases complexed with the FtsK translocase at specialized dif sites, resolves dimeric chromosomes into free monomers to allow efficient chromosome segregation at cell division. Computational genome analysis of Helicobacter pylori, a slow growing gastric pathogen, identified just one chromosomal xer gene (xerH) and its cognate dif site (difH). Here we show that recombination between directly repeated difH sites requires XerH, FtsK but not XerT, the TnPZ transposon associated recombinase. xerH inactivation was not lethal, but resulted in increased DNA per cell, suggesting defective chromosome segregation. The xerH mutant also failed to colonize mice, and was more susceptible to UV and ciprofloxacin, which induce DNA breakage, and thereby recombination and chromosome dimer formation. xerH inactivation and overexpression each led to a DNA segregation defect, suggesting a role for Xer recombination in regulation of replication. In addition to chromosome dimer resolution and based on the absence of genes for topoisomerase IV (parC, parE) in H. pylori, we speculate that XerH may contribute to chromosome decatenation, although possible involvement of H. pylori's DNA gyrase and topoisomerase III homologue are also considered. Further analyses of this system should contribute to general understanding of and possibly therapy development for H. pylori, which causes peptic ulcers and gastric cancer; for the closely related, diarrheagenic Campylobacter species; and for unrelated slow growing pathogens that lack topoisomerase IV, such as Mycobacterium tuberculosis

Nothing Lasts Forever: Environmental Discourses on the Collapse of Past Societies

The study of the collapse of past societies raises many questions for the theory and practice of archaeology. Interest in collapse extends as well into the natural sciences and environmental and sustainability policy. Despite a range of approaches to collapse, the predominant paradigm is environmental collapse, which I argue obscures recognition of the dynamic role of social processes that lie at the heart of human communities. These environmental discourses, together with confusion over terminology and the concepts of collapse, have created widespread aporia about collapse and resulted in the creation of mixed messages about complex historical and social processes

Funerary Pithoi in Bronze Age Crete: Their Introduction and Significance at the Threshold of Minoan Palatial Society

Toward the end of the third millennium B.C.E., Minoan funerary customs changed, and people began to favor the use of clay receptacles-pithoi or larnakes-for the bodies of the dead. This article offers a comprehensive study of the funerary pithoi of the period, comprising a review of the available material and its classification, distribution, and dating, the relation of container to tomb types, and the specific use of pithoi within funerary ritual. It also assesses the importance of pithoi as an investment in terms of the material wealth that they represent and the knowledge of the complex techniques of handling dead bodies that they require. Finally, it examines the symbolic connotations of the pithos and argues that its wide adoption was part of a general turn toward the concept of the regeneration of life. This concept shifted the emphasis of the funerary realm toward the social dimension-namely, toward the reallocation of the roles and resources of the dead among the living. Such a shift helped people come to terms with contemporary social reality and shaped the agency of emerging elites, which led to the establishment of the first Minoan palaces and transformed Crete from a series of kin-based communities to a group of proto-states