Inter-root movement of Azospirillum brasilense and subsequent root colonization of crop and weed seedlings growing in soil

Inter-root movement and dispersion of the beneficial bacterium Azospirillum brasilense were monitored in root systems of wheat seedlings growing in the field and in growth chamber soil trays. Two strains were used, a motile wild-type strain (Cd, mot⁺) and a motility deficient strain (mot^–), which was derived from the Cd strain. Root colonization by two wild-type strains (Cd and Sp-245) was studied in 64 plant species growing in pots in the greenhouse. The two wild-type strains of A. brasilense were capable of colonizing all tested plant species. In soil trays and in the field, mot⁺ cells moved from inoculated roots to non-inoculated roots of either wheat plants or weeds growing in the same field plot, but the mot^– strain did not move toward non-inoculated roots of either plant species. In the field, both mot⁺ and mot^– strains of A. brasilense survived well in the rhizosphere of wheat for 30 days, but only mot⁺ moved between different weeds, regardless of the species, botanical family, or whether they were annuals or perennials. In plant-free, water-saturated soils, either in columns or in the field, both strains remained at the inoculation site and did not move.It is proposed (a) that A. brasilense is not a plant-specific bacterium and that (b) colonization of the entire root system in soil is an active process determined by bacterial motility; it is not plant specific, but depends on the presence of plants. Correspondence to: Y. Bashan     

On the Origins and Control of Community Types in the Human Microbiome

Microbiome-based stratification of healthy individuals into compositional categories, referred to as “enterotypes” or “community types”, holds promise for drastically improving personalized medicine. Despite this potential, the existence of community types and the degree of their distinctness have been highly debated. Here we adopted a dynamic systems approach and found that heterogeneity in the interspecific interactions or the presence of strongly interacting species is sufficient to explain community types, independent of the topology of the underlying ecological network. By controlling the presence or absence of these strongly interacting species we can steer the microbial ecosystem to any desired community type. This open-loop control strategy still holds even when the community types are not distinct but appear as dense regions within a continuous gradient. This finding can be used to develop viable therapeutic strategies for shifting the microbial composition to a healthy configuration.     

Extracting Behaviorally Relevant Traits from Natural Stimuli: Benefits of Combinatorial Representations at the Accessory Olfactory Bulb

For many animals, chemosensation is essential for guiding social behavior. However, because multiple factors can modulate levels of individual chemical cues, deriving information about other individuals via natural chemical stimuli involves considerable challenges. How social information is extracted despite these sources of variability is poorly understood. The vomeronasal system provides an excellent opportunity to study this topic due to its role in detecting socially relevant traits. Here, we focus on two such traits: a female mouse’s strain and reproductive state. In particular, we measure stimulus-induced neuronal activity in the accessory olfactory bulb (AOB) in response to various dilutions of urine, vaginal secretions, and saliva, from estrus and non-estrus female mice from two different strains. We first show that all tested secretions provide information about a female’s receptivity and genotype. Next, we investigate how these traits can be decoded from neuronal activity despite multiple sources of variability. We show that individual neurons are limited in their capacity to allow trait classification across multiple sources of variability. However, simple linear classifiers sampling neuronal activity from small neuronal ensembles can provide a substantial improvement over that attained with individual units. Furthermore, we show that some traits are more efficiently detected than others, and that particular secretions may be optimized for conveying information about specific traits. Across all tested stimulus sources, discrimination between strains is more accurate than discrimination of receptivity, and detection of receptivity is more accurate with vaginal secretions than with urine. Our findings highlight the challenges of chemosensory processing of natural stimuli, and suggest that downstream readout stages decode multiple behaviorally relevant traits by sampling information from distinct but overlapping populations of AOB neurons.     

Aminergic Receptors in Drosophila melanogaster: Responsiveness of Adenylate Cyclase to Putative Neurotransmitters

Adenylate cyclase in Drosophila melanogaster heads is stimulated 5-6-fold by low concentrations of octopamine. The octopamine stimulation is inhibited by low concentrations of the alpha-adrenergic ligands phentolamine and dihydroergotamine and of chlorpromazine, but not by low concentrations of the beta-antagonist propranolol and by the alpha-antagonist yohimbine. d-Tubocurarine enhances the octopamine effect. Tyramine, norepinephrine, and epinephrine also stimulate the cyclase, probably via the octopamine receptor. Serotonin and dopamine stimulate Drosophila adenylate cyclase 1.3-1.4-fold; at least the latter putative neurotransmitter seems to interact with a receptor distinct from the octopamine receptor. Prolonged incubation with dopamine in vitro abolishes adenylate cyclase basal activity as well as responsiveness to guanyl nucleotides, NaF, and putative neurotransmitters.     

A note on a new defined medium for 'Pseudomonas tomato'

A synthetic medium based on d -galactose as a single carbon source and either l -asparagine, l -glutamine or l -threonine as a single nitrogen source has been developed for Pseudomonas tomato. The growth of Ps. tomato on this medium was equal to its growth on commonly used complex media.     

Phage display and crystallographic analysis reveals potential substrate/binding site interactions in the protein secretion chaperone CsaA from Agrobacterium tumefaciens

The protein CsaA has been proposed to function as a protein secretion chaperone in bacteria that lack the Sec-dependent protein-targeting chaperone SecB. CsaA is a homodimer with two putative substrate-binding pockets, one in each monomer. To test the hypothesis that these cavities are indeed substrate-binding sites able to interact with other polypeptide chains, we selected a peptide that bound to CsaA from a random peptide library displayed on phage. Presented here is the structure of CsaA from Agrobacterium tumefaciens (AtCsaA) solved in the presence and absence of the selected peptide. To promote co-crystallization, the sequence for this peptide was genetically fused to the amino-terminus of AtCsaA. The resulting 1.65 Å resolution crystal structure reveals that the tethered peptide from one AtCsaA molecule binds to the proposed substrate-binding pocket of a symmetry-related molecule possibly mimicking the interaction between a pre-protein substrate and CsaA. The structure shows that the peptide lies in an extended conformation with alanine, proline and glutamine side chains pointing into the binding pocket. The peptide interacts with the atoms of the AtCsaA-binding pocket via seven direct hydrogen bonds. The side chain of a conserved pocket residue, Arg76, has an “up” conformation when the CsaA-binding site is empty and a “down” conformation when the CsaA-binding site is occupied, suggesting that this residue may function to stabilize the peptide in the binding cavity. The presented aggregation assays, phage-display analysis and structural analysis are consistent with AtCsaA being a general chaperone. The properties of the proposed CsaA-binding pocket/peptide interactions are compared to those from other structurally characterized molecular chaperones.     

The Oxytocin Receptor (OXTR) Contributes to Prosocial Fund Allocations in the Dictator Game and the Social Value Orientations Task

Background

Economic games observe social decision making in the laboratory that involves real money payoffs. Previously we have shown that allocation of funds in the Dictator Game (DG), a paradigm that illustrates costly altruistic behavior, is partially determined by promoter-region repeat region variants in the arginine vasopressin 1a receptor gene (AVPR1a). In the current investigation, the gene encoding the related oxytocin receptor (OXTR) was tested for association with the DG and a related paradigm, the Social Values Orientation (SVO) task.

Methodology/Principal Findings

Association (101 male and 102 female students) using a robust-family based test between 15 single tagging SNPs (htSNPs) across the OXTR was demonstrated with both the DG and SVO. Three htSNPs across the gene region showed significant association with both of the two games. The most significant association was observed with rs1042778 (p = 0.001). Haplotype analysis also showed significant associations for both DG and SVO. Following permutation test adjustment, significance was observed for 2–5 locus haplotypes (p<0.05). A second sample of 98 female subjects was subsequently and independently recruited to play the dictator game and was genotyped for the three significant SNPs found in the first sample. The rs1042778 SNP was shown to be significant for the second sample as well (p = 0.004, Fisher''s exact test).

Conclusions

The demonstration that genetic polymorphisms for the OXTR are associated with human prosocial decision making converges with a large body of animal research showing that oxytocin is an important social hormone across vertebrates including Homo sapiens. Individual differences in prosocial behavior have been shown by twin studies to have a substantial genetic basis and the current investigation demonstrates that common variants in the oxytocin receptor gene, an important element of mammalian social circuitry, underlie such individual differences.     

Infiltrating Blood-Derived Macrophages Are Vital Cells Playing an Anti-inflammatory Role in Recovery from Spinal Cord Injury in Mice

Background

Although macrophages (MΦ) are known as essential players in wound healing, their contribution to recovery from spinal cord injury (SCI) is a subject of debate. The difficulties in distinguishing between different MΦ subpopulations at the lesion site have further contributed to the controversy and led to the common view of MΦ as functionally homogenous. Given the massive accumulation in the injured spinal cord of activated resident microglia, which are the native immune occupants of the central nervous system (CNS), the recruitment of additional infiltrating monocytes from the peripheral blood seems puzzling. A key question that remains is whether the infiltrating monocyte-derived MΦ contribute to repair, or represent an unavoidable detrimental response. The hypothesis of the current study is that a specific population of infiltrating monocyte-derived MΦ is functionally distinct from the inflammatory resident microglia and is essential for recovery from SCI.

Methods and Findings

We inflicted SCI in adult mice, and tested the effect of infiltrating monocyte-derived MΦ on the recovery process. Adoptive transfer experiments and bone marrow chimeras were used to functionally distinguish between the resident microglia and the infiltrating monocyte-derived MΦ. We followed the infiltration of the monocyte-derived MΦ to the injured site and characterized their spatial distribution and phenotype. Increasing the naïve monocyte pool by either adoptive transfer or CNS-specific vaccination resulted in a higher number of spontaneously recruited cells and improved recovery. Selective ablation of infiltrating monocyte-derived MΦ following SCI while sparing the resident microglia, using either antibody-mediated depletion or conditional ablation by diphtheria toxin, impaired recovery. Reconstitution of the peripheral blood with monocytes resistant to ablation restored the lost motor functions. Importantly, the infiltrating monocyte-derived MΦ displayed a local anti-inflammatory beneficial role, which was critically dependent upon their expression of interleukin 10.

Conclusions

The results of this study attribute a novel anti-inflammatory role to a unique subset of infiltrating monocyte-derived MΦ in SCI recovery, which cannot be provided by the activated resident microglia. According to our results, limited recovery following SCI can be attributed in part to the inadequate, untimely, spontaneous recruitment of monocytes. This process is amenable to boosting either by active vaccination with a myelin-derived altered peptide ligand, which indicates involvement of adaptive immunity in monocyte recruitment, or by augmenting the naïve monocyte pool in the peripheral blood. Thus, our study sheds new light on the long-held debate regarding the contribution of MΦ to recovery from CNS injuries, and has potentially far-reaching therapeutic implications. Please see later in the article for Editors'' Summary