Interaction of effect on secretion of alkaline phosphatase from E. coli by charge of the N-terminal part of the signal peptide and proteins SecB and SecA

The cytoplasmic step of posttranslational secretion in Escherichia coli is catalyzed by export-specific chaperone SecB and translocational ATPase SecA. In addition, the efficiency of secretion depends on the charge of the signal peptide (SP). Substitution of positively charged Lys(-20) with noncharged Ala or negatively charged Glu in the N-terminal region of SP of the alkaline phosphatase (PhoA) precursor (prePhoA) was shown to decrease the PhoA secretion in the periplasm. The effect on secretion increased in the absence of SecB and was especially high on SecA inactivation. A change in SP charge strengthened the SecA and SecB dependences of secretion. On evidence of immunoprecipitation, the charge of the N-terminal region of SP had no effect on prePhoA interaction with the cytoplasmic secretion factors, suggesting no direct binding between this region and SecA or SecB. Yet the charge of the N-terminal region proved to affect the functions of SP as an intramolecular chaperone and a factor of prePhoA targeting to the membrane in cooperation with SecA and SecB.     

Concentrations and ecological risks of metals in surface sediments of some coastal creeks in the Niger Delta,Nigeria

The concentrations of nine metals were measured by atomic absorption spectrophotometry in surface sediments of three coastal creeks, namely, the Ifie, Egbokodo and Ubeji creeks, in the Niger Delta of Nigeria, from August 2012 to January 2013. The aim of the study was to provide information on the spatial and seasonal distribution patterns, degree of contamination, and ecological risks of metals in these sediments. The mean concentrations of the nine metals in these creek sediments ranged from 0.30 to 3.20?mg kg^?1 Cd; 10.7 to 24.7?mg kg^?1 Pb, 125 to 466?mg kg^?1 Cr; 3.1.10 to 14.9?mg kg^?1 Cu; 4.7 to 14.3?mg kg^?1 Co; 61.1 to 115?mg kg^?1 Ni; 106 to 183?mg kg^?1 Mn; 52.0 to 170?mg kg^?1 Zn and 5 469 to 20 639?mg kg^?1 Fe. In general, the metal concentrations were higher in the dry season than the wet season, except for Cr. The concentrations of Cd, Cr, Ni and Zn were above their regulatory control limits in sediment as specified by the Nigerian Regulatory Authority and Cd was identified as the main ecological risk factor. The enrichment factors for the studied metals followed the order: Cd > Cr > Ni > Zn > Pb > Co > Mn > Cu. The average multiple pollution index values indicated that these sediments were severely polluted with significant inputs from Cd, Ni and Cr.     

Species associations and trait dissimilarity in communities of ectoparasitic arthropods harboured by small mammals at three hierarchical scales

1. This study tested the relationships between the probability of pairwise species co-occurrence and pairwise dissimilarity in their traits in infracommunities (across assemblages harboured by conspecific individual hosts within a locality), component communities (across assemblages harboured by host species within a locality), and compound communities (across assemblages in different localities) of fleas and gamasid mites parasitic on small mammals in Western Siberia. 2. A significant, albeit weak, tendency was found for flea communities harboured by conspecific host individuals, host species, and host communities to be composed of similar species. No relationship between the probability of co-occurrence and trait dissimilarity was detected for mite communities at any hierarchical scale. 3. For fleas, this study explained the link between positive co-occurrence and trait dissimilarity by a process resembling environmental filtering realised mainly via host traits for infracommunities and component communities and via off-host environment for compound communities, thus suggesting that the identical shape of the relationships between co-occurrence and trait dissimilarity at different scales was driven by different mechanisms. 4. The explanation of the lack of this relationship in mites included: (i) the paucity of the subset of mite traits used in this study and its potential inadequacy for the question at hand; and (ii) possible masking of the effect induced by one trait on co-occurrence owing to the lack of this effect induced by another trait(s). 5. Caution is recommended regarding the compilation of a dataset involving multiple traits, its analysis, and the interpretation of the results.     

Contrasting responses of beta diversity components to environmental and host-associated factors in insect ectoparasites

1. The present study investigated whether different components (species replacement and species gains/losses) of compositional and phylogenetic beta diversity of insect ectoparasites responded similarly to environmental and host-associated gradients using a large dataset on distribution of fleas and their rodent hosts in Mongolia. 2. Generalised dissimilarity modelling was applied to investigate whether environmental variables or host dissimilarity was the best predictor of species/lineage replacement and species/lineage gains/losses (= richness difference) components of compositional and phylogenetic flea beta diversity. 3. The total compositional beta diversity of fleas was influenced mainly by the gradient in air temperature and, to a lesser degree, by total host beta diversity, with the former effect being associated with the richness difference component and the latter effect being associated with species replacement component. The total phylogenetic beta diversity of fleas was best explained by the total phylogenetic beta diversity of hosts, with this effect being mainly associated with the lineage replacement component, whereas the lineage richness difference component responded mainly to the temperature gradient. 4. The results of the present indicate that not only multiple beta diversity facets are driven by different factors, but also different components of the same beta diversity facet respond to different environmental (for parasites, including host-associated) gradients. These patterns were masked when only total beta diversity was analysed. 5. This emphasizes the importance of considering the components of insect beta diversity separately. Ignoring the separate components of beta diversity can lead to potentially erroneous inferences about the relative contribution of abiotic and biotic effects on beta diversity.     

Is abundance a species attribute? An example with haematophagous ectoparasites

Population density is a fundamental property of a species and yet it varies among populations of the same species. The variation comes from the interplay between intrinsic features of a species that tend to produce repeatable density values across all populations of the same species and extrinsic environmental factors that differ among localities and thus tend to produce spatial variation in density. Is inter-population variation in density too large for density to be considered a true species character? We addressed this question using data on abundance (number of parasites per individual host, i.e. equivalent to density) of fleas ectoparasitic on small mammals. The data included samples of 548 flea populations, representing 145 flea species and obtained from 48 different geographical regions. Abundances of the same flea species on the same host species, but in different regions, were more similar to each other than expected by chance, and varied significantly among flea species, with 46% of the variation among samples accounted by differences between flea species. Thus, estimates of abundance are repeatable within the same flea species. The same repeatability was also observed, but to a lesser extent, across flea genera, tribes and subfamilies. Independently of the identity of the flea species, abundance values recorded on the same host species, or in the same geographical region, also showed significant statistical repeatability, though not nearly as strong as that associated with abundance values from the same flea species. There were also no strong indications that regional differences in abiotic variables were an important determinant of variation in abundance of a given flea species on a given host species. Abundance thus appears to be a true species trait in fleas, although it varies somewhat within bounds set by species-specific life history traits.     

Analysis of Ca2+/Mg2+ selectivity in α‐lactalbumin and Ca2+‐binding lysozyme reveals a distinct Mg2+‐specific site in lysozyme

The triggering of Ca²⁺ signaling pathways relies on Ca²⁺/Mg²⁺ specificity of proteins mediating these pathways. Two homologous milk Ca²⁺‐binding proteins, bovine α‐lactalbumin (bLA) and equine lysozyme (EQL), were analyzed using the simplest “four‐state” scheme of metal‐ and temperature‐induced structural changes in a protein. The association of Ca²⁺/Mg²⁺ by native proteins is entropy‐driven. Both proteins exhibit strong temperature dependences of apparent affinities to Ca²⁺ and Mg²⁺, due to low thermal stabilities of their apo‐forms and relatively high unfavorable enthalpies of Mg²⁺ association. The ratios of their apparent affinities to Ca²⁺ and Mg²⁺, being unusually high at low temperatures (5.3–6.5 orders of magnitude), reach the values inherent to classical EF‐hand motifs at physiological temperatures. The comparison of phase diagrams predicted within the model of competitive Ca²⁺ and Mg²⁺ binding with experimental data strongly suggests that the association of Ca²⁺ and Mg²⁺ ions with bLA is a competitive process, whereas the primary Mg²⁺ site of EQL is different from its Ca²⁺‐binding site. The later conclusion is corroborated by qualitatively different molar ellipticity changes in near‐UV region accompanying Mg²⁺ and Ca²⁺ association. The Ca²⁺/Mg²⁺ selectivity of Mg²⁺‐site of EQL is below an order of magnitude. EQL exhibits a distinct Mg²⁺‐specific site, probably arising as an adaptation to the extracellular environment. Proteins 2010. © 2010 Wiley‐Liss, Inc.     

Patterns of zeta diversity in ectoparasite communities harboured by small mammals at three hierarchical scales: taxon-invariance and scale-dependence

Oecologia - We studied compositional turnover in communities of fleas and mites harboured by small mammals using zeta diversity metric (similarity between multiple communities) and asked whether...