BackgroundThe bacterial Hfq protein is able to interact with diverse RNA molecules, including regulatory small non-coding RNAs (sRNAs), and thus it is recognized as a global post-transcriptional regulator of gene expression. Loss of Hfq has an extensive impact in bacterial physiology which in several animal pathogens influences virulence. Sinorhizobium meliloti is a model soil bacterium known for its ability to establish a beneficial nitrogen-fixing intracellular symbiosis with alfalfa. Despite the predicted general involvement of Hfq in the establishment of successful bacteria-eukaryote interactions, its function in S. meliloti has remained unexplored.ResultsTwo independent S. meliloti mutants, 2011-3.4 and 1021Δhfq, were obtained by disruption and deletion of the hfq gene in the wild-type strains 2011 and 1021, respectively, both exhibiting similar growth defects as free-living bacteria. Transcriptomic profiling of 1021Δhfq revealed a general down-regulation of genes of sugar transporters and some enzymes of the central carbon metabolism, whereas transcripts specifying the uptake and metabolism of nitrogen sources (mainly amino acids) were more abundant than in the wild-type strain. Proteomic analysis of the 2011-3.4 mutant independently confirmed these observations. Symbiotic tests showed that lack of Hfq led to a delayed nodulation, severely compromised bacterial competitiveness on alfalfa roots and impaired normal plant growth. Furthermore, a large proportion of nodules (55%-64%) elicited by the 1021Δhfq mutant were non-fixing, with scarce content in bacteroids and signs of premature senescence of endosymbiotic bacteria. RT-PCR experiments on RNA from bacteria grown under aerobic and microoxic conditions revealed that Hfq contributes to regulation of nifA and fixK1/K2, the genes controlling nitrogen fixation, although the Hfq-mediated regulation of fixK is only aerobiosis dependent. Finally, we found that some of the recently identified S. meliloti sRNAs co-inmunoprecipitate with a FLAG-epitope tagged Hfq protein.ConclusionsOur results support that the S. meliloti RNA chaperone Hfq contributes to the control of central metabolic pathways in free-living bacteria and influences rhizospheric competence, survival of the microsymbiont within the nodule cells and nitrogen fixation during the symbiotic interaction with its legume host alfalfa. The identified S. meliloti Hfq-binding sRNAs are predicted to participate in the Hfq regulatory network.

Aims:  This work was conducted to identify the antifungal compounds produced by two previously isolated Bacillus sp. strains: ARP23 and MEP218. Both strains were subjected to further analysis to determine their taxonomic position and to identify the compounds responsible for their antifungal activity as well as to evaluate the efficiency of these strains to control sclerotinia stem rot in soybean. Methods and Results:  The antifungal compounds were isolated by acid precipitation of cell‐free supernatants, purified by RP‐HPLC and then tested for antagonistic activity against Sclerotinia sclerotiorum. Mass spectra from RP‐HPLC eluted fractions showed the presence of surfactin C15, fengycins A (C16–C17) and B (C16) isoforms in supernatants from strain ARP23 cultures, whereas the major lipopeptide produced by strain MEP218 was iturin A C15. Alterations in mycelial morphology and sclerotial germination were observed in the presence of lipopeptides‐containing supernatants from Bacillus strains cultures. Foliar application of Bacillus amyloliquefaciens strains on soybean plants prior to S. sclerotiorum infection resulted in significant protection against sclerotinia stem rot compared with noninoculated plants or plants inoculated with a nonlipopeptide‐producing B. subtilis strain. Conclusions:  Both strains, renamed as B. amyloliquefaciens ARP23 and MEP218, were able to produce antifungal compounds belonging to the cyclic lipopeptide family. Our data suggest that the foliar application of lipopeptide‐producing B. amyloliquefaciens strains could be a promising strategy for the management of sclerotinia stem rot in soybean. Significance and Impact of the Study:  Sclerotinia stem rot was ranked as one of the most severe soybean disease in Argentina and worldwide. The results of this study showed the potential of B. amyloliquefaciens strains ARP23 and MEP218 to control plant diseases caused by S. sclerotiorum.

Aims. We present fundamental stellar parameters, chemical abundances, and rotational velocities for a sample of 86 evolved stars with planets (56 giants; 30 subgiants), and for a control sample of 137 stars (101 giants; 36 subgiants) without planets. The analysis was based on both high signal-to-noise and resolution echelle spectra. The main goals of this work are i) to investigate chemical differences between evolved stars that host planets and those of the control sample without planets; ii) to explore potential differences between the properties of the planets around giants and subgiants; and iii) to search for possible correlations between these properties and the chemical abundances of their host stars. Implications for the scenarios of planet formation and evolution are also discussed. Methods. The fundamental stellar parameters (T eff , log g, [Fe/H], ξ t ) were computed homogeneously using the FUNDPAR code. The chemical abundances of 14 elements (Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Zn, and Ba) were obtained using the MOOG code. Rotational velocities were derived from the full width at half maximum of iron isolated lines. Results. In agreement with previous studies, we find that subgiants with planets are, on average, more metal-rich than subgiants without planets by ∼0.16 dex. The [Fe/H] distribution of giants with planets is centered at slightly subsolar metallicities and there is no metallicity enhancement relative to the [Fe/H] distribution of giants without planets. Furthermore, contrary to recent results, we do not find any clear difference between the metallicity distributions of stars with and without planets for giants with M > 1.5 M . With regard to the other chemical elements, the analysis of the [X/Fe] distributions shows differences between giants with and without planets for some elements, particularly V, Co, and Ba. Subgiants with and without planets exhibit similar behavior for most of the elements. On the other hand, we find no evidence of rapid rotation among the giants with planets or among the giants without planets. Finally, analyzing the planet properties, some interesting trends might be emerging: i) multi-planet systems around evolved stars show a slight metallicity enhancement compared with single-planet systems; ii) planets with a 0.5 AU orbit subgiants with [Fe/H] > 0 and giants hosting planets with a 1 AU have [Fe/H] < 0; iii) higher-mass planets tend to orbit more metal-poor giants with M ≤ 1.5 M , whereas planets around subgiants seem to follow the planet-mass metallicity trend observed on dwarf hosts; iv) [X/Fe] ratios for Na, Si, and Al seem to increase with the mass of planets around giants; v) planets orbiting giants show lower orbital eccentricities than those orbiting subgiants and dwarfs, suggesting a more efficient tidal circularization or the result of the engulfment of close-in planets with larger eccentricities.

The interaction between Azospirillum brasilense and plants is not fully understood, although several bacterial surface components like exopolysaccharides (EPS), flagella, and capsular polysaccharides are required for attachment and colonization. While in other plantb acteria associations (Rhizobium^legume, Pseudomonas^potato), lipopolysaccharides (LPS) play a key role in the establishment of an effective association, their role in the root colonization by Azospirillum had not been determined. In this study, we isolated a Tn5 mutant of A. brasilense Cd (EJ1) with an apparently modified LPS core structure, non-mucoid colony morphology, increased EPS production, and affected in maize root colonization. A 3790-bp region revealed the presence of three complete open reading frames designated rmlC, rmlB and rmlD. The beginning of a fourth open reading frame was found and designated rmlA. These genes are organized in a cluster which shows homology to the cluster involved in the synthesis of dTDP-rhamnose in other bacteria. Additionally, the analysis of the monosaccharide composition of LPSs showed a diminution of rhamnose compared to the wild-type strain. ß