Multilevel Selection in Models of Prebiotic Evolution II: A Direct Comparison of Compartmentalization and Spatial Self-Organization

Multilevel selection has been indicated as an essential factor for the evolution of complexity in interacting RNA-like replicator systems. There are two types of multilevel selection mechanisms: implicit and explicit. For implicit multilevel selection, spatial self-organization of replicator populations has been suggested, which leads to higher level selection among emergent mesoscopic spatial patterns (traveling waves). For explicit multilevel selection, compartmentalization of replicators by vesicles has been suggested, which leads to higher level evolutionary dynamics among explicitly imposed mesoscopic entities (protocells). Historically, these mechanisms have been given separate consideration for the interests on its own. Here, we make a direct comparison between spatial self-organization and compartmentalization in simulated RNA-like replicator systems. Firstly, we show that both mechanisms achieve the macroscopic stability of a replicator system through the evolutionary dynamics on mesoscopic entities that counteract that of microscopic entities. Secondly, we show that a striking difference exists between the two mechanisms regarding their possible influence on the long-term evolutionary dynamics, which happens under an emergent trade-off situation arising from the multilevel selection. The difference is explained in terms of the difference in the stability between self-organized mesoscopic entities and externally imposed mesoscopic entities. Thirdly, we show that a sharp transition happens in the long-term evolutionary dynamics of the compartmentalized system as a function of replicator mutation rate. Fourthly, the results imply that spatial self-organization can allow the evolution of stable folding in parasitic replicators without any specific functionality in the folding itself. Finally, the results are discussed in relation to the experimental synthesis of chemical Darwinian systems and to the multilevel selection theory of evolutionary biology in general. To conclude, novel evolutionary directions can emerge through interactions between the evolutionary dynamics on multiple levels of organization. Different multilevel selection mechanisms can produce a difference in the long-term evolutionary trend of identical microscopic entities

Phenotypic detection of various β-lactamases among multidrug resistant isolates of Escherichia coli and Klebseilla pneumoniae isolated from urinary tract infections in some Egyptian hospitals

In the present study a total of 205 isolates were recovered from186 different cases from urinary tract infections ward in some Egyptian hospitals (Dar El-Fouad Hospital, EL-Demerdash Hospital, El-Sheikh Zayed Hospital and Kasr Al-Ainy Hospital) from September 2011 to October 2012. The most predominant bacteria isolated from urine samples was Escherichia coli 49.76% (102/205), followed by Klebseilla pneumonia represented 14.63% (35/205). The growing number and rapid increase in antibiotic resistance among E. coli, Klebsiella spp. has prompted us to investigate the resistance mechanisms among these isolates. It was found that the rates of potential ESβL production among isolates of E. coli and Klebsiella spp. were 46.08% (47/102) and 60% (21/35) respectively. While, the rates of potential ESβLs and AmpC β-lactamase production among E. coli and Klebsiella spp., were 22.55% (23/102) and 25.71% (9/35), respectively. Our study revealed that the rates of carbapenemases production among E. coli and Klebsiella spp. were 0.98% (1/102) and 8.57% (3/35), respectively

Continuum Approaches to Understanding Ion and Peptide Interactions with the Membrane

Experimental and computational studies have shown that cellular membranes deform to stabilize the inclusion of transmembrane (TM) proteins harboring charge. Recent analysis suggests that membrane bending helps to expose charged and polar residues to the aqueous environment and polar head groups. We previously used elasticity theory to identify membrane distortions that minimize the insertion of charged TM peptides into the membrane. Here, we extend our work by showing that it also provides a novel, computationally efficient method for exploring the energetics of ion and small peptide penetration into membranes. First, we show that the continuum method accurately reproduces energy profiles and membrane shapes generated from molecular simulations of bare ion permeation at a fraction of the computational cost. Next, we demonstrate that the dependence of the ion insertion energy on the membrane thickness arises primarily from the elastic properties of the membrane. Moreover, the continuum model readily provides a free energy decomposition into components not easily determined from molecular dynamics. Finally, we show that the energetics of membrane deformation strongly depend on membrane patch size both for ions and peptides. This dependence is particularly strong for peptides based on simulations of a known amphipathic, membrane binding peptide from the human pathogen Toxoplasma gondii. In total, we address shortcomings and advantages that arise from using a variety of computational methods in distinct biological contexts