Heterogeneity in arbuscular mycorrhizal fungal communities may contribute to inconsistent plant-soil feedback in a Neotropical forest

Background and aims

Plant-soil feedback may vary across host species and environmental gradients. The relative importance of these biotic versus abiotic drivers of feedback will determine the stability of plant and microbial communities across environments. If plant hosts are the main driver of soil microbial communities, plant-soil feedback may be stable across changing environments. However, if microbial communities vary with environmental gradients, feedback may also vary, limiting its capacity to predict plant distributions.

Methods

We characterized arbuscular mycorrhizal (AM) fungi across tree plantations and a primary Neotropical rainforest. We then performed a plant-soil feedback pot experiment of AM fungi from these plantations on three plant species and related feedback and AM fungal communities in the field.

Results

In the field, temporal and spatial variation in AM fungal composition was similar in magnitude to variation across plant host species. Composition of AM fungi in the pot experiment significantly differed from the field plots. Furthermore, differential feedback was explained by shifts in AM fungal composition only for one plant host species (Hyeronima alchorneoides) in the pot experiment.

Conclusions

Natural AM fungal communities were temporally and spatially heterogeneous and AM fungal communities in the greenhouse did not reflect natural soils. These factors led to heterogeneous and unpredictable feedback responses, which suggests that applying greenhouse derived plant-soil feedback trends to predict plant coexistence in natural systems may be misleading.

     

P-glycoprotein Restricts Ocular Penetration of Loperamide across the Blood-Ocular Barriers: a Comparative Study in Mdr1a Knock-out and Wild Type Sprague Dawley Rats

The current research was undertaken to determine the existence and magnitude of P-glycoprotein (P-gp) expression on the blood-ocular barriers by studying the ocular penetration of loperamide, a specific P-gp substrate, in P-gp (Mdr1a) knock-out (KO) and wild type (WT) Sprague Dawley rats. A clear, stable, sterile solution of loperamide (1 mg/mL), for intravenous administration, was formulated and evaluated. Ocular distribution was studied in P-gp KO and WT rats following intravenous administration of loperamide (at two doses). The drug levels in plasma, aqueous humor (AH), and vitreous humor (VH) samples were determined with the aid of UHPLC-Q-TOF-MS/MS, and the AH/plasma (D _AH ) and VH/plasma (D _VH ) distribution ratios were estimated. Electroretinography (ERG), ultrastructural analyses, and histology studies were carried out, in both KO and WT rats, to detect any drug-induced functional and/or structural alterations in the retina. Dose-related loperamide levels were observed in the plasma of both WT and KO rats. The loperamide concentrations in the AH and VH of KO rats were significantly higher compared to that observed in the WT rats, at the lower dose. However, a marked increase in the D _AH and D _VH was noted in the KO rats. ERG, ultrastructure, and histology studies did not indicate any drug-induced toxic effects in the retina under the test conditions. The results from these studies demonstrate that P-gp blocks the penetration of loperamide into the ocular tissues from the systemic circulation and that the effect is more pronounced at lower plasma loperamide concentrations.     

Clinical infection in house rats (<Emphasis Type="Italic">Rattus rattus</Emphasis>) caused by <Emphasis Type="Italic">Streptobacillus notomytis</Emphasis>

Rat bite fever is an under-reported, under-diagnosed emerging zoonosis with worldwide distribution. Besides Spirillum minus, Streptobacillus moniliformis is the major causative microorganism although it usually colonises rats without any clinical signs. A group of house rats (Rattus rattus) kept in a zoo exhibition for educational purposes suffered from neurological signs including disorientation, torticollis, stall walking, ataxia and death. Gross pathological and histo-pathological examinations of the investigated rats revealed high-grade otitis interna et media, from which Streptobacillus notomytis was isolated in pure culture or as the predominant microorganism. This case series underlines a previously expressed hypothesis that R. rattus might be naturally colonised with S. notomytis, whereas the traditional rat bite fever organism, S. moniliformis, might be restricted to the Norway rat (Rattus norvegicus). However, the general paucity of Streptobacillus isolates, especially from their respective animal hosts, precludes definitive proof of these host tropisms. This is the first report of S. notomytis detection outside Asia and Australia and the first evidence for its role as a facultative pathogen in house rats.     

Phosphorus speciation and micro-scale spatial distribution in North-American temperate agricultural soils from micro X-ray fluorescence and X-ray absorption near-edge spectroscopy

Background and Aims

Phosphorus (P) is an essential nutrient for plants but its low availability often necessitates amendments for agronomical issues. Objectives were to determine P spatial distribution and speciation that remain poorly understood in cultivated soils.

Methods

Aquic Argiudoll soil samples developed on a calcareous loam glacial till were collected from experimental plots submitted to contrasting crop rotations and amendments. Micro-X-ray fluorescence (μ-XRF) maps were collected on undisturbed samples. X-ray absorption near edge structure (XANES) spectra were collected on bulk samples and on fractions thereof, and on points of interests selected from μ-XRF maps. Results were compared with chemical analyses and extraction techniques results.

Results

Chemical analyses show variations in total and exchangeable P contents depending on the samples but no significant difference is observed in terms of P distribution and speciation. P distribution is dominated by a low-concentration diffuse background with a minor contribution from minute hot spots. P speciation is dominated by phosphate groups bound to clay-humic complexes. No modification of P distribution and speciation is observed close to roots.

Conclusions

This study evidenced minor effect of cropping and fertilizing practices on P speciation in cultivated soils. Despite analytical challenges, the combined use of μ-XRF and XANES provides relevant information on P speciation in heterogeneous soil media.

     

Sex-specific differences in hepatic steatosis in obese spontaneously hypertensive (SHROB) rats

Background

Patients with metabolic syndrome, who are characterized by co-existence of insulin resistance, hypertension, hyperlipidemia, and obesity, are also prone to develop non-alcoholic fatty liver disease (NAFLD). Although the prevalence and severity of NAFLD is significantly greater in men than women, the mechanisms by which gender modulates the pathogenesis of hepatic steatosis are poorly defined. The obese spontaneously hypertensive (SHROB) rats represent an attractive model of metabolic syndrome without overt type 2 diabetes. Although pathological manifestation caused by the absence of a functional leptin receptor has been extensively studied in SHROB rats, it is unknown whether these animals elicited sex-specific differences in the development of hepatic steatosis.

Methods

We compared hepatic pathology in male and female SHROB rats. Additionally, we examined key biochemical and molecular parameters of signaling pathways linked with hyperinsulinemia and hyperlipidemia. Finally, using methods of quantitative polymerase chain reaction (qPCR) and western blot analysis, we quantified expression of 45 genes related to lipid biosynthesis and metabolism in the livers of male and female SHROB rats.

Results

We show that all SHROB rats developed hepatic steatosis that was accompanied by enhanced expression of SREBP1, SREBP2, ACC1, and FASN proteins. The livers of male rats also elicited higher induction of Pparg, Ppara, Slc2a4, Atox1, Skp1, Angptl3, and Pnpla3 mRNAs. In contrast, the livers of female SHROB rats elicited constitutively higher levels of phosphorylated JNK and AMPK and enhanced expression of Cd36.

Conclusion

Based on these data, we conclude that the severity of hepatic steatosis in male and female SHROB rats was mainly driven by increased de novo lipogenesis. Moreover, male and female SHROB rats also elicited differential severity of hepatic steatosis that was coupled with sex-specific differences in fatty acid transport and esterification.

     

Rodent-Borne <Emphasis Type="Italic">Bartonella</Emphasis> Infection Varies According to Host Species Within and Among Cities

It is becoming increasingly likely that rodents will drive future disease epidemics with the continued expansion of cities worldwide. Though transmission risk is a growing concern, relatively little is known about pathogens carried by urban rats. Here, we assess whether the diversity and prevalence of Bartonella bacteria differ according to the (co)occurrence of rat hosts across New Orleans, LA (NO), where both Norway (Rattus norvegicus) and roof rats (Rattus rattus) are found, relative to New York City (NYC) which only harbors Norway rats. We detected human pathogenic Bartonella species in both NYC and New Orleans rodents. We found that Norway rats in New Orleans harbored a more diverse assemblage of Bartonella than Norway rats in NYC and that Norway rats harbored a more diverse and distinct assemblage of Bartonella compared to roof rats in New Orleans. Additionally, Norway rats were more likely to be infected with Bartonella than roof rats in New Orleans. Flea infestation appears to be an important predictor of Bartonella infection in Norway rats across both cities. These findings illustrate that pathogen infections can be heterogeneous in urban rodents and indicate that further study of host species interactions could clarify variation in spillover risk across cities.     

Active Transport of Membrane Components by Self-Organization of the Min Proteins

Heterogeneous distribution of components in the biological membrane is critical in the process of cell polarization. However, little is known about the mechanisms that can generate and maintain the heterogeneous distribution of the membrane components. Here, we report that the propagating wave patterns of the bacterial Min proteins can impose steric pressure on the membrane, resulting in transport and directional accumulation of the component in the membrane. Therefore, the membrane component waves represent transport of the component in the membrane that is caused by the steric pressure gradient induced by the differential levels of binding and dissociation of the Min proteins in the propagating waves on the membrane surface. The diffusivity, majorly influenced by the membrane anchor of the component, and the repulsed ability, majorly influenced by the steric property of the membrane component, determine the differential spatial distribution of the membrane component. Thus, transportation of the membrane component by the Min proteins follows a simple physical principle, which resembles a linear peristaltic pumping process, to selectively segregate and maintain heterogeneous distribution of materials in the membrane.

The absence of saturated pyrimidine bases in chromatin-associated RNA from avian reticulocytes and mouse ascites cells

Low molecular weight RNA (3–4S) has been isolated from the chromatin of avian reticulocytes and mouse ascites cells by the procedures used to isolated chromosomal RNA¹. Although dihydrouridine was readily detected in tRNA, neither this base, nor dihydroribothymidine, was found in detectable levels in chromatin-associated RNA or ribosomal RNA. The presence of saturated pyrimidines is not an invariant property of chromosomal RNA.