Legumes form a symbiotic association with rhizobia and fix atmospheric nitrogen in specialized root organs known as nodules. It is well known that salt stress inhibits root nodule symbiosis by decreasing rhizobial growth, rhizobial infection, nodule number, and nitrogenase activity in diverse legumes. Despite this knowledge, the genetic and molecular mechanisms governing salt stress\'s inhibition of nodulation and nitrogen fixation are still elusive. In this Viewpoint, we summarize the most recent knowledge of the genetic mechanisms that shape this symbiosis according to the salt levels in the soil. We emphasize the relevance of modulating the activity of the transcription factor Nodule Inception to properly shape the symbiosis with rhizobia accordingly. We also highlight the knowledge gaps that are critical for gaining a deeper understanding of the molecular mechanisms underlying the adaptation of the root nodule symbiosis to salt-stress conditions. We consider that filling these gaps can help to improve legume nodulation and harness its ecological benefits even under salt-stress conditions.

Peritonitis is a serious complication associated with high morbidity and mortality in patients with peritoneal dialysis (PD). We present a case of PD-associated peritonitis caused by the unusual pathogen Rhizobium. After therapy failure and bacterial growth despite treatment with vancomycin and tobramycin, the treatment was changed to meropenem intravenously and ciprofloxacin intraperitoneally according to antimicrobial susceptibility testing. The patient subsequently recovered without having the PD-catheter removed. To conclude, patients with PD are one of many patient groups at a greater risk of infections with unusual microbial agents, and pathogens that normally do not cause disease should be considered as potential causes of pathology when antibiotic treatment failure occurs.

Bradyrhizobia are Gram-negative soil bacteria that regroup a growing number of species. They are widespread in nature and recovered from various biomes that may be explained by a high genetic diversity in this genus. Among the numerous metabolic properties they can harbor, the nitrogen fixation resulting from the association with plants among which important crop legumes (soya bean, peanut, cowpea …) is of great interest, notably in a context of sustainable development. Metabarcoding is widely applied to study biodiversity from complex microbial communities. Here, we demonstrate that using a new species-specific and highly polymorphic 16S-23S rRNA intergenic spacer barcode, we could rapidly estimate the diversity of bradyrhizobial populations that associate with cowpea and peanut plants, two crop legumes of major interest in Senegal. Application of the method on indigenous bradyrhizobia associated with peanut and cowpea grown in soils collected in the center of the peanut basin shows that Bradyrhizobium vignae is a dominant symbiont. We also showed that the two plant species associate with distinct community profiles and that strains introduced by inoculation significantly modified the population structure with these two plants suggesting that application of elite strains as inoculants may well ensure optimized symbiotic performance. This approach may further be used to study the diversity of bradyrhizobia from contrasting agro-eco-climatic zones, to test whether the plant genotype influences the association outputs as well as to estimate the competitiveness for nodule occupancy and the fate of elite strains inoculated in the field.Key points• An amplicon sequencing approach targeting the Bradyrhizobium genus was developed.• Diversity of cowpea and peanut bradyrhizobia from cultivated soils was identified.• The method is well suited to test the competitiveness of defined Bradyrhizobium inoculants.

Urban agriculture, while being a promising solution to increase food sovereignty in cities, can lead to an unprecedented discharge of nutrient and fertilizer-related emissions into the urban environment. Especially relevant are nitrogen (N) and phosphorus (P), due to their contribution to marine and freshwater eutrophication. Therefore, alternative methods of fertilization need to be put into practice to avoid such impacts to the surrounding environment. Struvite, has been studied as a potential slow releasing fertilizer due to its high P content, while the bacteria rhizobium has been used to fix N directly from the atmosphere. Legumes, like the common bean are N-demanding crops capable of symbiosis with the bacteria rhizobium and have previously shown positive responses to fertilization with struvite. This study aims to analyze the environmental performance of plant production in hydroponic systems combining rhizobium inoculation and struvite (2 g, 5 g, 10 g, 20 g) irrigated with a N and P deficient nutrient solution, using life cycle analysis (LCA). The nutrient content of in- and out-going irrigation was analyzed as well as in plants and beans. The functional unit for the LCA was 1 kg of fresh beans. The results obtained indicate a yield reduction of 60% to 50% in comparison to the control which was irrigated with a full nutrient solution. The impacts from operational stage are less in all impact categories, where most significant reductions up to 69% and 59% are seen in marine-eutrophication and global warming respectively. Although the infrastructure does not change between treatments, its impacts increase due to the lower yields. We determine that below a 10% of the control yield, the alternative systems have more impact than the use of conventional mineral fertilizers in almost all impact categories, thus pointing to the importance of infrastructure to truly reduce environmental impacts for urban agriculture.

Rhizobium radiobacter is an aerobic, gram negative, rod-shaped, bacterium typically found in the soil. Commonly a plant pathogen, it is also a rare human pathogen causing serious disease. Risk factors for infection include neutropenia, leukopenia, catheters, hospitalization, and low CD4+ lymphocyte count, especially in patients with malignancy or human immunodeficiency virus. There is currently limited literature to establish a definitive guideline for antimicrobial therapy and obtaining susceptibilities from a specialized laboratory is appropriate. We present a successfully treated case of R. radiobacter bioprosthetic mitral valve endocarditis in a patient with previous S. epidermidis endocarditis.

BACKGROUND: Repeated oscillations in intracellular calcium (Ca2+) concentration, known as Ca2+ spiking signals, have been described in plants for a limited number of cellular responses to biotic or abiotic stimuli and most notably the common symbiotic signaling pathway (CSSP) which mediates the recognition by their plant hosts of two endosymbiotic microbes, arbuscular mycorrhizal (AM) fungi and nitrogen fixing rhizobia. The detailed analysis of the complexity and variability of the Ca2+ spiking patterns which have been revealed in recent studies requires both extensive datasets and sophisticated statistical tools.
RESULTS: As a contribution, we have developed automated Ca2+ spiking analysis (CaSA) software that performs i) automated peak detection, ii) statistical analyses based on the detected peaks, iii) autocorrelation analysis of peak-to-peak intervals to highlight major traits in the spiking pattern.We have evaluated CaSA in two experimental studies. In the first, CaSA highlighted unpredicted differences in the spiking patterns induced in Medicago truncatula root epidermal cells by exudates of the AM fungus Gigaspora margarita as a function of the phosphate concentration in the growth medium of both host and fungus. In the second study we compared the spiking patterns triggered by either AM fungal or rhizobial symbiotic signals. CaSA revealed the existence of different patterns in signal periodicity, which are thought to contribute to the so-called Ca2+ signature.
CONCLUSIONS: We therefore propose CaSA as a useful tool for characterizing oscillatory biological phenomena such as Ca2+ spiking.

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Symbiotic nitrogen fixation is the main route for sustainable input of nitrogen into ecosystems. Nitrogen fixation in agriculture can be improved by inoculation of legume crops with suitable rhizobia. Knowledge of the biodiversity of rhizobia and of local populations is important for the design of successful inoculation strategies. Soybeans are major nitrogen-fixing crops in many parts of the world. Bradyrhizobial inoculants for soybean are very diverse, yet classification and characterization of strains have long been difficult. Recent genetic characterization methods permit more reliable identification and will improve our knowledge of local populations. Forage legumes form another group of agronomically important legumes. Research and extension policies valorizing rhizobial germplasm diversity and preservation, farmer training for proper inoculant use and legal enforcement of commercial inoculant quality have proved a successful approach to promoting the use of forage legumes while enhancing biological N(2) fixation. It is worth noting that taxonomically important strains may not necessarily be important reference strains for other uses such as legume inoculation and genomics due to specialization of the different fields. This article points out both current knowledge and gaps remaining to be filled for further interaction and improvement of a rhizobial commons.

The first evidence that plants represent a valid, safe and cost-effective alternative to traditional expression systems for large-scale production of antigens and antibodies was described more than 10 years ago. Since then, considerable improvements have been made to increase the yield of plant-produced proteins. These include the use of signal sequences to target proteins to different cellular compartments, plastid transformation to achieve high transgene dosage, codon usage optimization to boost gene expression, and protein fusions to improve recombinant protein stability and accumulation. Thus, several HIV/SIV antigens and neutralizing anti-HIV antibodies have recently been successfully expressed in plants by stable nuclear or plastid transformation, and by transient expression systems based on plant virus vectors or Agrobacterium-mediated infection. The current article gives an overview of plant expressed HIV antigens and antibodies and provides an account of the use of different strategies aimed at increasing the expression of the accessory multifunctional HIV-1 Nef protein in transgenic plants.

Agrobacterium tumefaciens is a phytopathogenic bacterium that induces the \'crown gall\' disease in plants by transfer and integration of a segment of its tumor-inducing (Ti) plasmid DNA into the genome of numerous plant species that represent most of the higher plant families. Recently, it has been shown that, under laboratory conditions, the host range of Agrobacterium can be extended to non-plant eukaryotic organisms. These include yeast, filamentous fungi, cultivated mushrooms and human cultured cells. In this article, we present Agrobacterium-mediated transformation of non-plant organisms as a source of new protocols for genetic transformation, as a unique tool for genomic studies (insertional mutagenesis or targeted DNA integration) and as a useful model system to study bacterium-host cell interactions. Moreover, better knowledge of the DNA-transfer mechanisms from bacteria to eukaryotic organisms can also help in understanding horizontal gene transfer--a driving force throughout biological evolution.