Molecular tool development in traditionally non-tractable animals opens new avenues to study gene functions in the relevant ecological context. Entomopathogenic nematodes (EPN) Steinernema and their symbiotic bacteria of Xenorhabdus spp are a valuable experimental system in the laboratory and are applicable in the field to promote agricultural productivity. The infective juvenile (IJ) stage of the nematode packages mutualistic symbiotic bacteria in the intestinal pocket and invades insects that are agricultural pests. The lack of consistent and heritable genetics tools in EPN targeted mutagenesis severely restricted the study of molecular mechanisms underlying both parasitic and mutualistic interactions. Here, I report a protocol for CRISPR-Cas9 based genome-editing that is successful in two EPN species, S. carpocapsae and S. hermaphroditum. I adapted a gonadal microinjection technique in S. carpocapsae, which created on-target modifications of a homologue Sc-dpy-10 (cuticular collagen) by homology directed repair. A similar delivery approach was used to introduce various alleles in S. hermaphroditum including Sh-dpy-10 and Sh-unc-22 (a muscle gene), resulting in visible and heritable phenotypes of dumpy and twitching, respectively. Using conditionally dominant alleles of Sh-unc-22 as a co-CRISPR marker, I successfully modified a second locus encoding Sh-Daf22 (a homologue of human sterol carrier protein SCPx), predicted to function as a core enzyme in the biosynthesis of nematode pheromone that is required for IJ development. As a proof of concept, Sh-daf-22 null mutant showed IJ developmental defects in vivo (in insecta). This research demonstrates that Steinernema spp are highly tractable for targeted mutagenesis and has great potential in the study of gene functions under controlled laboratory conditions within the relevant context of its ecological niche.

In exponential population growth, variability in the timing of individual division events and environmental factors (including stochastic inoculation) compound to produce variable growth trajectories. In several stochastic models of exponential growth we show power-law relationships that relate variability in the time required to reach a threshold population size to growth rate and inoculum size. Population-growth experiments in E.coli and S.aureus with inoculum sizes ranging between 1 and 100 are consistent with these relationships. We quantify how noise accumulates over time, finding that it encodes-and can be used to deduce-information about the early growth rate of a population.

Boron substitution represents a promising approach to stabilize carbon clathrate structures, but no thermodynamically stable substitution schemes have been identified for frameworks other than the type-VII (sodalite) structure type. To investigate the possibility for additional tetrahedral carbon-based clathrate networks, more than 5000 unique boron decoration schemes were investigated computationally for type-I and type-II carbon clathrates with a range of guest elements including Li, Na, K, Rb, Cs, Mg, Ca, Sr, and Ba. Density functional theory calculations were performed at 10 and 50 GPa, and the stability and impact of boron substitution were evaluated. The results indicate that the boron-substituted carbon clathrates are stabilized under high-pressure conditions. Full cage occupancies of intermediate-sized guest atoms (e.g., Na, Ca, and Sr) are the most favorable energetically. Clathrate stability is maximized when the boron atoms are substituted within the hexagonal rings of the large [51262]/[51264] cages. Several structures with favorable formation enthalpies <-200 meV/atom were predicted, and type-I Ca8B16C30 is on the convex hull at 50 GPa. This structure represents the first thermodynamically stable type-I clathrate identified and suggests that boron-substituted carbon clathrates may represent a large family of diamond-like framework materials with a range of structure types and guest/framework substitutions.

There is concern that the time taken to publish academic papers in microbiological science has significantly increased in recent years. While the data do not specifically support this, evidence suggests that editors are having to invite more and more reviewers to identify those willing to perform peer review.

The origin of Earth's volatile elements is highly debated. Comparing the chalcogen isotope ratios in the bulk silicate Earth (BSE) to those of its possible building blocks, chondritic meteorites, allows constraints on the origin of Earth's volatiles; however, these comparisons are complicated by potential isotopic fractionation during protoplanetary differentiation, which largely remains poorly understood. Using first-principles calculations, we find that core-mantle differentiation does not notably fractionate selenium and tellurium isotopes, while equilibrium evaporation from early planetesimals would enrich selenium and tellurium in heavy isotopes in the BSE. The sulfur, selenium, and tellurium isotopic signatures of the BSE reveal that protoplanetary differentiation plays a key role in establishing most of Earth's volatile elements, and a late veneer does not substantially contribute to the BSE's volatile inventory.