Inoculation of Mimosa Pudica with Paraburkholderia phymatum Results in Changes to the Rhizoplane Microbial Community Structure.

Nitrogen fixing symbiosis between rhizobia and legumes contributes significant amounts of N to agricultural and natural environments. In natural soils, rhizobia compete with indigenous bacterial communities to colonize legume roots, which leads to symbiotic interactions. However, limited information is currently available on the effects of the rhizobial symbiont on the resident microbial community in the legume rhizosphere, rhizoplane, and endosphere, which is partly due to the presence of native nodulating rhizobial strains. In the present study, we used a symbiotic system comprised of Paraburkholderia phymatum and Mimosa pudica to examine the interaction of an inoculant strain with indigenous soil bacteria. The effects of a symbiont inoculation on the native bacterial community was investigated using high throughput sequencing and an analysis of 16S rRNA gene amplicons. The results obtained revealed that the inoculation induced significant alterations in the microbial community present in the rhizoplane+endosphere of the roots, with 13 different taxa showing significant changes in abundance. No significant changes were observed in the rhizospheric soil. The relative abundance of P. phymatum significantly increased in the rhizoplane+endosphere of the root, but significant decreased in the rhizospheric soil. While the rhizosphere, rhizoplane, and root endosphere contained a wide diversity of bacteria, the nodules were predominantly colonized by P. phymatum. A network analysis revealed that the operational taxonomic units of Streptomyces and Phycicoccus were positively associated with P. phymatum as potential keystone taxa. Collectively, these results suggest that the success of an inoculated symbiont depends on its ability to colonize the roots in the face of competition by other soil bacteria. A more detailed understanding of the mechanisms by which an inoculated strain colonizes its plant host is crucial for realizing the full potential of microbial inoculants in sustainable agriculture.

Dopamine-induced sulfatase and its regulator are required for Salmonella enterica serovar Typhimurium pathogenesis.

Catecholamine hormones enhance the virulence of pathogenic bacteria. Studies in the 1980s made intriguing observations that catecholamines were required for induction of sulfatase activity in many enteric pathogens, including Salmonella enterica serovar Typhimurium. In this report, we show that STM3122 and STM3124, part of horizontally acquired Salmonella pathogenesis island 13, encode a catecholamine-induced sulfatase and its regulator, respectively. Induction of sulfatase activity was independent of the well-studied QseBC and QseEF two-component regulatory systems. S. Typhimurium 14028S mutants lacking STM3122 or STM3124 showed reduced virulence in zebrafish. Because catecholamines are inactivated by sulfation in the mammalian gut, S. Typhimurium could utilize CA-induced sulfatase to access free catecholamines for growth and virulence.

Establishment of a murine culture system for modeling the temporal progression of cranial and trunk neural crest cell differentiation.

The neural crest (NC) is a transient population of embryonic progenitors that are implicated in a diverse range of congenital birth defects and pediatric syndromes. The broad spectrum of NC-related disorders can be attributed to the wide variety of differentiated cell types arising from the NC. In vitro models of NC development provide a powerful platform for testing the relative contributions of intrinsic and extrinsic factors mediating NC differentiation under normal and pathogenic conditions. Although differentiation is a dynamic process that unfolds over time, currently, there is no well-defined chronology that characterizes the in vitro progression of NC differentiation towards specific cell fates. In this study, we have optimized culture conditions for expansion of primary murine NC cells that give rise to both ectodermal and mesoectodermal derivatives, even after multiple passages. Significantly, we have delineated highly reproducible timelines that include distinct intermediate stages for lineage-specific NC differentiation in vitro In addition, isolating both cranial and trunk NC cells from the same embryos enabled us to make direct comparisons between the two cell populations over the course of differentiation. Our results define characteristic changes in cell morphology and behavior that track the temporal progression of NC cells as they differentiate along the neuronal, glial and chondrogenic lineages in vitro These benchmarks constitute a chronological baseline for assessing how genetic or environmental disruptions may facilitate or impede NC differentiation. Introducing a temporal dimension substantially increases the power of this platform for screening drugs or chemicals for developmental toxicity or therapeutic potential. This article has an associated First Person interview with the first author of the paper.

Exposure to ZnO nanoparticles alters neuronal and vascular development in zebrafish: Acute and transgenerational effects mitigated with dissolved organic matter.

Exposure to ZnO-nanoparticles (NPs) in embryonic zebrafish reduces hatching rates which can be mitigated with dissolved organic material (DOM). Although hatching rate can be a reliable indicator of toxicity and DOM mitigation potential, a fish that has been exposed to ZnO-NPs or any other toxicant may also exhibit other abnormal phenotypes not readily detected by the unaided eye. In this study, we moved beyond hatching rate analysis to investigate the consequences of ZnO-NPs exposure on the nervous and vascular systems in developing zebrafish. Zebrafish exposed to ZnO-NPs (1-100 ppm) exhibited an array of cellular phenotypes including: abnormal secondary motoneuron (SMN) axonal projections, abnormal dorsal root ganglion development and abnormal blood vessel development. Dissolved Zn (<10 kDa) exposure also caused abnormal SMN axonal projections, but to a lesser extent than ZnO-NPs. The ZnO-NPs-induced abnormal phenotypes were reversed in embryos concurrently exposed with various types of DOM. In these acute mitigation exposure experiments, humic acid and carbohydrate, along with natural organic matter obtained from the Suwannee River in Georgia and Milwaukee River in Wisconsin, were the best mitigators of ZnO-NPs-induced motoneuron toxicity at 96 h post fertilization. Further experiments were performed to determine if the ZnO-NPs-induced, abnormal axonal phenotypes and the DOM mitigated axonal phenotypes could persist across generations. Abnormal SMN axon phenotypes caused by ZnO-NPs-exposure were detected in F1 and F2 generations. These are fish that have not been directly exposed to ZnO-NPs. Fish mitigated with DOM during the acute exposure (F0 generation) had a reduction in abnormal motoneuron axon errors in larvae of subsequent generations. Therefore, ZnO-NPs exposure results in neurotoxicity in developing zebrafish which can persist from one generation to the next. Mitigation with DOM can reverse the abnormal phenotypes in an acute embryonic exposure context, as well as across generations, resulting in healthy fish.

Benzalkonium chloride, benzethonium chloride, and chloroxylenol - Three replacement antimicrobials are more toxic than triclosan and triclocarban in two model organisms.

With the recent ban of triclosan (TCS) and triclocarban (TCC) from some personal care products, many replacement antimicrobial compounds have been used. Yet the potential health risk and environmental impact of these replacement compounds are largely unknown. Here we investigated the toxicological effects of three commonly used replacement antimicrobials, benzalkonium chloride (BAC), benzethonium chloride (BEC), and chloroxylenol (CX) to two model organisms, the nematode C. elegans and zebrafish (Danio rerio), and compared them to the banned TCS and TCC. We found that these replacement compounds are not any safer than the banned antimicrobials. In the worm, at least one of the three, BAC, showed comparable toxicity to TCS from organismal to molecular levels, with toxic effects occurring at lower hundred µg/L to lower mg/L levels. In the fish, all three compounds at the tested concentration ranges (0.05-5 mg/L) showed toxicity effects to zebrafish embryos, indicated by hatching delay or inhibition, embryonic mortality, morphological malformations, and neurotoxicity. BAC was the most toxic among the three, with acute lethal toxicity occurring at environmentally relevant concentrations (hundreds of µg/L), which is comparable to the banned TCC. However, the toxicity effects of BAC and TCC occurred within different time windows, potentially suggesting different mechanisms of toxicity. CX was the only compound that induced a "body curvature" phenotype among the five compounds examined, suggesting a unique mode of toxic action for this compound. Furthermore, all five compounds except TCS induced neurotoxicity in fish larvae, indicated by alterations in secondary motoneuron axonal projections. Such neurotoxicity has been largely understudied for these antimicrobials in the past years and calls for further investigations in terms of its underlying mechanisms and ecological significance. These findings strongly indicate that scrutiny should be put on these replacement compounds before their introduction into massive use in personal care products.