Root associated iron oxidizing bacteria increase phosphate nutrition and influence root to shoot partitioning of iron in tolerant plant Typha angustifolia

Aims

Typha angustifolia is a heavy metal tolerant plant that grows in a uranium mine tailings highly contaminated with iron. In this study three iron oxidizing microbes (FeOBs) isolated from Typha rhizoplane were investigated for their role in plant growth promotion (PGP). Their effect on iron nutrition in Typha under iron replete and excess condition was also evaluated.

Methods

The PGP activities of the FeOBs were studied by measuring their influence on plant growth. To investigate the mechanism of growth promotion their ability to solubilize phosphate, and to produce Indole acetic acid and siderophores were studied. The influence of the FeOBs on root to shoot partitioning of iron was tested by measuring total iron content in roots and shoots treated with microbes.

Results

The FeOBs were named as Paenibacillus cookii JGR8, (MTCC12002), Pseudomonas jaduguda JGR2 (LMG25820) and Bacillus megaterium JGR9 (MTCC12001). The siderophore producers, influenced iron accumulation in the plant root. Additionally P. pseudoalcaligenes JGR2 increased shoot iron content overcoming the root- shoot barrier that allows Typha to exclude metals from its shoot. Among the PGP mechanisms tested, ability to solubilize phosphate appeared to be most significant for increasing the plant biomass.

Conclusion

FeOBs that produce siderophore increased iron content in plant and therefore can be of immense biotechnological importance. However Biomass increase was directly correlated with increased phosphate acquisition and not with enhanced iron accumulation in Typha.     

Instability of novel ant-fungal associations constrains horizontal exchange of fungal symbionts

One of the more fascinating features of fungus-gardening ants (Attini: Formicidae) is their fidelity to their lineage-specific fungal symbionts. Among the derived higher-attine ants (leafcutter ants and close relatives), it is thought that most leaf-cutting ants grow Attamyces fungus whereas most Trachymyrmex ants grow ‘Trachymyces’ fungus, but there exist exceptions to this clade-to-clade correspondence between ants and fungi. The exceptions are inconsistent with strict one-to-one coevolution, which suggests that ants sometimes are able to switch to novel fungi. Such switches appear to be largely constrained and ants are generally faithful to their species-specific fungi. Prior experiments demonstrated no clear fitness consequences of growing novel fungi over the short-term when the ant Trachymyrmex septentrionalis was symbiont-switched by forcing it to grow Attamyces leaf-cutter fungus. We hypothesized that long-term ant-fungal fidelity is constrained either by physiological differences among fungal species or by garden diseases that symbiont-switched ants cannot control. Repeat experiments in a different location show that T. septentrionalis colonies switched to grow Attamyces exhibit sudden declines in garden biomass and consequent fitness reductions due to garden destruction by pathogens, whereas control colonies (Trachymyrmex ants cultivating Trachymyces fungus) do not show parallel garden declines. These patterns are mirrored in symbiont-switch experiments conducted on colonies in Trachymyrmex turrifex. Disease microbes selecting on ant-cultivar combinations therefore can constrain switches to novel cultivars and maintain combinations that are more resistant to disease.     

Characterization and reactivity of broiler chicken sera to selected recombinant Campylobacter jejuni chemotactic proteins

Campylobacter jejuni, a Gram-negative rod bacterium, is the leading causative agent of human acute bacterial gastroenteritis worldwide. Consumption and handling of raw or undercooked poultry are regarded as a major source for human infection. Because bacterial chemotaxis guides microorganisms to colonization and invasion in the host cells, proteins involved in chemotactic processes can be novel targets for vaccine development. In this communication, we report amplification, cloning and expression of the C. jejuni chemotactic proteins in an Escherichia coli expression system. A total of 15 chemotactic protein genes were successfully expressed. These recombinant proteins were confirmed by nucleotide sequencing, SDS-PAGE analysis and immunoblot analysis of six-His and hemagglutinin tags. Twelve recombinant chemotactic proteins were further tested whether they were antigenic using sera from broiler chickens older than 4 weeks. The immunoblot results show that each chicken serum reacted to a variety of the recombinant proteins, but all sera reacted to the Cjj0473 gene product (annotated as a methyl-accepting chemotaxis protein), suggesting that anti-Campylobacter antibodies may be prevalent in the poultry population. These antibody screening results provide a rationale for further evaluation of the Cjj0473 protein as a potential vaccine for broilers to improve human food safety.     

Back to the future with the AGP–Ca2+ flux capacitor

Background

Arabinogalactan proteins (AGPs) are ubiquitous in green plants. AGPs comprise a widely varied group of hydroxyproline (Hyp)-rich cell surface glycoproteins (HRGPs). However, the more narrowly defined classical AGPs massively predominate and cover the plasma membrane. Extensive glycosylation by pendant polysaccharides O-linked to numerous Hyp residues like beads of a necklace creates a unique ionic compartment essential to a wide range of physiological processes including germination, cell extension and fertilization. The vital clue to a precise molecular function remained elusive until the recent isolation of small Hyp–arabinogalactan polysaccharide subunits; their structural elucidation by nuclear magentic resonance imaging, molecular simulations and direct experiment identified a 15-residue consensus subunit as a β-1,3-linked galactose trisaccharide with two short branched sidechains each with a single glucuronic acid residue that binds Ca²⁺ when paired with its adjacent sidechain.

Scope

AGPs bind Ca²⁺ (K_d ∼ 6 μm) at the plasma membrane (PM) at pH ∼5·5 but release it when auxin-dependent PM H⁺-ATPase generates a low periplasmic pH that dissociates AGP–Ca²⁺ carboxylates (pk_a ∼3); the consequential large increase in free Ca²⁺ drives entry into the cytosol via Ca²⁺ channels that may be voltage gated. AGPs are thus arguably the primary source of cytosolic oscillatory Ca²⁺ waves. This differs markedly from animals, in which cytosolic Ca²⁺ originates mostly from internal stores such as the sarcoplasmic reticulum. In contrast, we propose that external dynamic Ca²⁺ storage by a periplasmic AGP capacitor co-ordinates plant growth, typically involving exocytosis of AGPs and recycled Ca²⁺, hence an AGP–Ca²⁺ oscillator.

Conclusions

The novel concept of dynamic Ca²⁺ recycling by an AGP–Ca²⁺ oscillator solves the long-standing problem of a molecular-level function for classical AGPs and thus integrates three fields: AGPs, Ca²⁺ signalling and auxin. This accounts for the involvement of AGPs in plant morphogenesis, including tropic and nastic movements.     

The genome of African yam (Dioscorea cayenensis‐rotundata complex) hosts endogenous sequences from four distinct badnavirus species

Several endogenous viral elements (EVEs) have been identified in plant genomes, including endogenous pararetroviruses (EPRVs). Here, we report the first characterization of EPRV sequences in the genome of African yam of the Dioscorea cayenensis‐rotundata complex. We propose that these sequences should be termed ‘endogenous Dioscorea bacilliform viruses' (eDBVs). Molecular characterization of eDBVs shows that they constitute sequences originating from various parts of badnavirus genomes, resulting in a mosaic structure that is typical of most EPRVs characterized to date. Using complementary molecular approaches, we show that eDBVs belong to at least four distinct Badnavirus species, indicating multiple, independent, endogenization events. Phylogenetic analyses of eDBVs support and enrich the current taxonomy of yam badnaviruses and lead to the characterization of a new Badnavirus species in yam. The impact of eDBVs on diagnosis, yam germplasm conservation and movement, and breeding is discussed.     

Biological parameters of Scirtothrips dorsalis (Thysanoptera: Thripidae) on selected hosts

Since its establishment in Florida in 2005, Scirtothrips dorsalis Hood, a highly polyphagous species, has become an economically important pest of ornamental plants and a potentially significant pest of vegetable and fruit crops. Fruit and vegetable production in Florida is trending toward significant adoption of organic methods and use of widely dispersed small fields in rapidly urbanizing landscapes. Landscape plants may serve as refugia from which S. dorsalis recruits can disperse to nearby fruit and vegetable plantings. Therefore, information on this pest's biology including how it is affected by various host species is needed to develop effective integrated pest management (IPM) programs. In the greenhouse and laboratory condition, we studied the effects of various host plants, development, diel flight activity, oviposition, and demographics of S. dorsalis. The pest preferred Jalape?o pepper and Knockout rose over the other hosts, and it was most active between 1000 and 1600 hours EST. Irrespective of the host species, the duration of each of the immature stadia varied within a narrow range, and their respective sizes were quite similar. Demographic parameters quantified included gross reproduction rate (GRR), net reproductive rate (R(o)), intrinsic rate of increase per day (R(m)), finite rate of increase per day (λ), and mean generation time (T). The pest population may increase by a factor of ≈ 1.09/d, so that it may double in 8 or 9 d. The above information should be helpful in the development of sound programs to manage S. dorsalis on various crops and in the formulation of detection strategies by quarantine officers.     

The epidemiology of antibiotic resistance in Campylobacter

Antibiotic resistance, particularly with the fluoroquinolones and macrolide antibiotics, has now emerged globally with thermophilic campylobacters, including Campylobacter jejuni and C. coli, giving rise to concerns about how these organisms have acquired such resistance characteristics, as well as consequences for human and animal treatment. This review examines (i) the clinical epidemiology of antibiotic resistance in human and animal thermophilic campylobacters, (ii) an update on resistance rates globally, (iii) surveillance of antimicrobial resistance in campylobacters originating from animals, particularly poultry, (iv) the role of the environment in the acquisition and transmission of antibiotic-resistant campylobacters, as well as (v) issues of biocide resistance in campylobacters.     

HistoChoice® as an alternative to formalin fixation of undecalcified bone specimens

We compared histochemical and immunohistochemical staining as well as fluorochrome labeling in murine bone specimens that were fixed with 10% neutral buffered formalin to those fixed with HistoChoice®. We showed that sections from undecalcified tibiae fixed for 4 h in HistoChoice® resulted in enhanced toluidine blue and Von Kossa histochemical staining compared to formalin fixation. HistoChoice® produced comparable or improved staining for alkaline phosphatase. Acid phosphatase localization was better in formalin fixed specimens, but osteoclasts were visuralized more easily in HistoChoice® fixed specimens. As expected, immunohistochemical labeling was antibody dependent; some antibodies labeled better in HistoChoice® fixed specimens while others were better in formalin fixed specimens. Toluidine blue, Von Kossa, and alkaline phosphatase staining of sections fixed for 12 h produced sections that were similar to 4 h fixed sections. Fixation for 12 h preserved acid phosphatase activity better. Increasing fixation to 12 h affected immunolocalization differentially. Bone sialoprotein labeling in HistoChoice® fixed specimens was comparable to formalin fixed samples. On the other hand, after 12 h formalin fixation, osteocalcin labeling was comparable to HistoChoice®. For most histochemical applications, fixing murine bone specimens for 4 h with HistoChoice® yielded superior staining compared to formalin fixation. If immunohistochemical localization is desired, however, individual antibodies must be tested to determine which fixation process retains antigenicity better. In addition, there was no detectable difference in the intensity of fluorochrome labeling using either fixative. Finally, fixation duration did not alter the intensity of labeling.