Soil compartment is a major determinant of the impact of simulated rainfall on desert microbiota.

Although desert soils support functionally important microbial communities that affect plant growth and influence many biogeochemical processes, the impact of future changes in precipitation patterns on the microbiota and their activities is largely unknown. We performed in-situ experiments to investigate the effect of simulated rainfall on bacterial communities associated with the widespread perennial shrub, Rhazya stricta in Arabian desert soils. The bacterial community composition was distinct between three different soil compartments: surface biological crust, root-attached, and the broader rhizosphere. Simulated rainfall had no significant effect on the overall bacterial community composition, but some population-level responses were observed, especially in soil crusts where Betaproteobacteria, Sphingobacteria, and Bacilli became more abundant. Bacterial biomass in the nutrient-rich crust increased three-fold one week after watering, whereas it did not change in the rhizosphere, despite its much higher water retention. These findings indicate that between rainfall events, desert-soil microbial communities enter into stasis, with limited species turnover, and reactivate rapidly and relatively uniformly when water becomes available. However, microbiota in the crust, which was relatively enriched in nutrients and organic matter, were primarily water-limited, compared with the rhizosphere microbiota that were co-limited by nutrients and water.

Broad-scale predictability of carbohydrates and exopolymers in Antarctic and Arctic sea ice.

Sea ice can contain high concentrations of dissolved organic carbon (DOC), much of which is carbohydrate-rich extracellular polymeric substances (EPS) produced by microalgae and bacteria inhabiting the ice. Here we report the concentrations of dissolved carbohydrates (dCHO) and dissolved EPS (dEPS) in relation to algal standing stock [estimated by chlorophyll (Chl) a concentrations] in sea ice from six locations in the Southern and Arctic Oceans. Concentrations varied substantially within and between sampling sites, reflecting local ice conditions and biological content. However, combining all data revealed robust statistical relationships between dCHO concentrations and the concentrations of different dEPS fractions, Chl a, and DOC. These relationships were true for whole ice cores, bottom ice (biomass rich) sections, and colder surface ice. The distribution of dEPS was strongly correlated to algal biomass, with the highest concentrations of both dEPS and non-EPS carbohydrates in the bottom horizons of the ice. Complex EPS was more prevalent in colder surface sea ice horizons. Predictive models (validated against independent data) were derived to enable the estimation of dCHO concentrations from data on ice thickness, salinity, and vertical position in core. When Chl a data were included a higher level of prediction was obtained. The consistent patterns reflected in these relationships provide a strong basis for including estimates of regional and seasonal carbohydrate and dEPS carbon budgets in coupled physical-biogeochemical models, across different types of sea ice from both polar regions.

Bacterial polysaccharides suppress induced innate immunity by calcium chelation.

Bacterial pathogens and symbionts must suppress or negate host innate immunity. However, pathogens release conserved oligomeric and polymeric molecules or MAMPs (Microbial Associated Molecular Patterns), which elicit host defenses [1], [2] and [3]. Extracellular polysaccharides (EPSs) are key virulence factors in plant and animal pathogenesis, but their precise function in establishing basic compatibility remains unclear [4], [5], [6] and [7]. Here, we show that EPSs suppress MAMP-induced signaling in plants through their polyanionic nature [4] and consequent ability to chelate divalent calcium ions [8]. In plants, Ca2+ ion influx to the cytosol from the apoplast (where bacteria multiply [4], [5] and [9]) is a prerequisite for activation of myriad defenses by MAMPs [10]. We show that EPSs from diverse plant and animal pathogens and symbionts bind calcium. EPS-defective mutants or pure MAMPs, such as the flagellin peptide flg22, elicit calcium influx, expression of host defense genes, and downstream resistance. Furthermore, EPSs, produced by wild-type strains or purified, suppress induced responses but do not block flg22-receptor binding in Arabidopsis cells. EPS production was confirmed in planta, and the amounts in bacterial biofilms greatly exceed those required for binding of apoplastic calcium. These data reveal a novel, fundamental role for bacterial EPS in disease establishment, encouraging novel control strategies.

Chemical assessment of marine sediments in vicinity of Norwegian fish farms - A pilot study.

While aquaculture is growing rapidly all over the world and generating many economic benefits, so have the environmental concerns about the externalities posed by the fish-farming industry. The distribution profiles of organic compounds and inorganic elements were explored in marine surface sediments collected in proximity of two active Norwegian fish farms, Hestøya and Nørholmen (<200-1100 m from the perimeter edge of the installations). Overall, the sediment organic matter (SOM) content was 7.3 ± 4.9%, with 7.9 ± 5.1% and 4.0 ± 0.5% for Hestøya and Nørholmen, respectively. A non-targeted analysis was performed for screening organic compounds in marine sediments, and the presence of 60 compounds was detected. Among suspect compounds were alkanes, alkenes, aromatics, aldehydes, ketones, esters, alcohols, diols, polycyclic aromatic hydrocarbons (PAHs), terpenes and terpenoids. Heptanal, benzaldehyde, 4-oxoisophorone, 1,7-dimethylnaphthalene and 3-bromophenol were the most abundant compounds in marine sediments. In total, concentrations of 47 elements were measured, concentrations of As, Cd, Cr, Cu, Hg, Mo, Ni, Sn and Zn were strongly influenced by anthropogenic inputs, while concentrations of Ce, Co, Al, Fe and Ti were related to the geology of the local bedrock. The chemical composition of marine sediments was different at Hestøya and Nørholmen, indicating different anthropogenic inputs in these areas. In general, concentrations of toxic elements were below the proposed guidelines for Norwegian marine sediment quality and can be characterised as background pollution. Overall, fish-farming activities had only a minor or negligible influence on marine sediments and are unlikely to cause any harm to local aquatic life in the studied area.

Trace elements and polychlorinated biphenyls (PCBs) in terrestrial compartments of Svalbard, Norwegian Arctic.

Despite being a remote location, the Arctic is a major receptor for anthropogenic pollution transported from the mid-latitudes. Vegetation and underlying organic soils in the Norwegian Arctic, Svalbard were used to study the occurrences of polychlorinated biphenyls (PCBs) and trace elements. In this study, current concentrations of PCBs and trace elements, namely, Al, As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, S, Sb, U and Zn in the terrestrial compartments of Svalbard are presented. Samples were collected from Adventdalen near Longyearbyen and from areas in proximity to Ny-Ålesund. There was significant variability in soil organic matter (SOM) among the soils analysed (5.0%-72.1%), with the highest values detected in Ny-Ålesund. The concentrations of Al, As, Cr Cu, Fe, Pb and Ni were associated with the geology of the local bedrock. The concentrations of all elements, except for Cd, Hg and Zn, were higher in soils than those in the overlying vegetation layers. Mean concentrations of ∑PCBs were significantly higher in vegetation (6.90 ±â€¯0.81 ng g-1 dw) than the underlying organic soils (3.70 ±â€¯0.36 ng g-1 dw). An inverse correlation of PCBs with the elements originating from the local bedrock indicated that their concentrations were potentially impacted by atmospheric deposition. PCBs and Cd were strongly associated, proposing a potential concomitant source of origin in Svalbard. Concentrations of PCBs and trace elements measured herein were below the proposed guidelines for Norwegian soil quality.

Identifying metabolic pathways for production of extracellular polymeric substances by the diatom Fragilariopsis cylindrus inhabiting sea ice.

Diatoms are significant primary producers in sea ice, an ephemeral habitat with steep vertical gradients of temperature and salinity characterizing the ice matrix environment. To cope with the variable and challenging conditions, sea ice diatoms produce polysaccharide-rich extracellular polymeric substances (EPS) that play important roles in adhesion, cell protection, ligand binding and as organic carbon sources. Significant differences in EPS concentrations and chemical composition corresponding to temperature and salinity gradients were present in sea ice from the Weddell Sea and Eastern Antarctic regions of the Southern Ocean. To reconstruct the first metabolic pathway for EPS production in diatoms, we exposed Fragilariopsis cylindrus, a key bi-polar diatom species, to simulated sea ice formation. Transcriptome profiling under varying conditions of EPS production identified a significant number of genes and divergent alleles. Their complex differential expression patterns under simulated sea ice formation was aligned with physiological and biochemical properties of the cells, and with field measurements of sea ice EPS characteristics. Thus, the molecular complexity of the EPS pathway suggests metabolic plasticity in F. cylindrus is required to cope with the challenging conditions of the highly variable and extreme sea ice habitat.

Production and Characterization of the Intra- and Extracellular Carbohydrates and Polymeric Substances (EPS) of Three Sea-Ice Diatom Species, and Evidence for a Cryoprotective Role for EPS.

Diatoms and their associated extracellular polymeric substances (EPS) are major constituents of the microalgal assemblages present within sea ice. Yields and chemical composition of soluble and cell-associated polysaccharides produced by three sea-ice diatoms, Synedropsis sp., Fragilariopsis curta, and F. cylindrus, were compared. Colloidal carbohydrates (CC) contained heteropolysaccharides rich in mannose, xylose, galactose, and glucose. Synedropsis sp. CC consisted mainly of carbohydrates <8 kDa size, with relatively soluble EPS, compared to high proportions of less-soluble EPS produced by both Fragilariopsis spp. F. curta colloidal EPS contained high concentrations of amino sugars (AS). Both Fragilariopsis species had high yields of hot bicarbonate (HB) soluble EPS, rich in xylose, mannose, galactose, and fucose (and AS in F. cylindrus). All species had frustule-associated EPS rich in glucose-mannose. Nutrient limitation resulted in declines in EPS yields and in glucose content of all EPS fractions. Significant similarities between EPS fractions from cultures and different components of natural EPS from Antarctic sea ice were found. Increased salinity (52) reduced growth, but increased yields of EPS in Fragilariopsis cylindrus. Ice formation was inhibited byF. cylindrus, EPS, and by enhanced EPS content (additional xanthan gum) down to -12°C, with growth rate reduced in the presence of xanthan. Differences in the production and composition of EPS between Synedropsis sp. and Fragilariopsis spp., and the association between EPS, freezing and cell survival, supports the hypothesis that EPS production is a strategy to assist polar ice diatoms to survive the cold and saline conditions present in sea ice.

Antibacterial and antifungal activity of cicerfuran and related 2-arylbenzofurans and stilbenes.

Cicerfuran, 2-(2-methoxy-4,5-methylenedioxyphenyl)-6-hydroxybenzofuran, is an antifungal phytoalexin previously isolated from the roots of chickpea, Cicer spp. The synthesis of cicerfuran, five 2-arylbenzofuran analogues and nine stilbene intermediates was reported recently. The antimicrobial activities of these compounds were evaluated against two species of bacteria, Bacillus subtilis and Pseudomonas syringae, and four species of filamentous fungi, Aspergillus niger, Botrytis cinerea, Cladosporium herbarum and Monilinia aucupariae. Stilbenes with a free hydroxyl group were active against both bacteria and fungi with MICs in the range 25-100microg/ml. Cicerfuran was the only 2-arylbenzofuran that showed antimicrobial activity with MICs as low as 25microg/ml. Some aspects of the structure-activity relationship are discussed.

Microbe-associated molecular pattern (MAMP) signatures, synergy, size and charge: influences on perception or mobility and host defence responses.

Triggering of defences by microbes has mainly been investigated using single elicitors or microbe-associated molecular patterns (MAMPs), but MAMPs are released in planta as complex mixtures together with endogenous oligogalacturonan (OGA) elicitor. We investigated the early responses in Arabidopsis of calcium influx and oxidative burst induced by non-saturating concentrations of bacterial MAMPs, used singly and in combination: flagellin peptide (flg22), elongation factor peptide (elf18), peptidoglycan (PGN) and component muropeptides, lipo-oligosaccharide (LOS) and core oligosaccharides. This revealed that some MAMPs have additive (e.g. flg22 with elf18) and even synergistic (flg22 and LOS) effects, whereas others mutually interfere (flg22 with OGA). OGA suppression of flg22-induced defences was not a result of the interference with the binding of flg22 to its receptor flagellin-sensitive 2 (FLS2). MAMPs induce different calcium influx signatures, but these are concentration dependent and unlikely to explain the differential induction of defence genes [pathogenesis-related gene 1 (PR1), plant defensin gene 1.2 (PDF1.2) and phenylalanine ammonia lyase gene 1 (PAL1)] by flg22, elf18 and OGA. The peptide MAMPs are potent elicitors at subnanomolar levels, whereas PGN and LOS at high concentrations induce low and late host responses. This difference might be a result of the restricted access by plant cell walls of MAMPs to their putative cellular receptors. flg22 is restricted by ionic effects, yet rapidly permeates a cell wall matrix, whereas LOS, which forms supramolecular aggregates, is severely constrained, presumably by molecular sieving. Thus, MAMPs can interact with each other, whether directly or indirectly, and with the host wall matrix. These phenomena, which have not been considered in detail previously, are likely to influence the speed, magnitude, versatility and composition of plant defences.

The yjbEFGH locus in Escherichia coli K-12 is an operon encoding proteins involved in exopolysaccharide production.

The RcsCDB phosphorelay was originally identified as the main regulator of colanic acid biosynthesis in Escherichia coli K-12. However, recent transcriptomic analyses have identified more than 150 genes belonging to the Rcs regulon, including yjbE, yjbF, yjbG and yjbH. These genes are clustered on the genome and oriented in the same direction but their function remains unknown. In this work it is shown that yjbE, yjbF, yjbG and yjbH are transcribed as a single operon and it is confirmed that the expression of this operon is controlled by the Rcs phosphorelay, in a manner that is dependent on the auxiliary regulatory protein RcsA. Interestingly, Northern blot analysis revealed that the amount of yjbE transcripts in the cell is higher than the amount of yjbEFGH transcripts and it is proposed that this differential expression is mediated by the presence of a strong stem-loop structure in the yjbE-yjbF intergenic region. Finally, evidence is provided that the overexpression of yjbEFGH affects colony morphology and leads to the production of an extracellular polysaccharide that binds Congo red and toluidine blue-O.