Plant sex and phenological stage affect interactions with rhizosphere nematode communities

Background: In dioecious plants, females and males associate differently with mycorrhizal fungi, but interactions with other rhizosphere organisms are less well studied.

Aims: We investigated the effect of plant sex on rhizosphere nematode communities associated with Corema album, a dioecious shrub occurring in coastal habitats.

Methods: Rhizosphere samples were collected from males and females in three populations (150 plants), during fruiting and flowering. Nematode communities were characterised and compared between plant sexes through statistical analyses of the abundance of trophic groups, plant parasitic nematode (PPN) genera and ecological indices.

Results: Free-living nematodes showed no statistically significant differences owing to plant sex. Conversely, PPN community composition was significantly different between plant sexes during fruiting but not flowering, suggesting that physiological requirements over the annual phenological cycle of the plant influence ecological interactions with the rhizosphere.

Of the 13 PPN genera identified, the ectoparasitic Criconema and Hemicriconemellawere more abundant in the rhizosphere of males during fruiting, whereas the endoparasitic Meloidogyne associated more frequently with females, suggesting that plant host suitability is related to PPN feeding strategy.

Conclusions: It appears that interactions of individuals of different sexes of C. album with the rhizosphere nematode community vary with phenological stage, especially for PPN.     

Where Are Socioeconomically Deprived Immigrants Located in Chile? A Spatial Analysis of Census Data Using an Index of Multiple Deprivation from the Last Three Decades (1992-2012)

Introduction and Purpose of the Study

Immigrants in Chile have diverse characteristics and include socioeconomically deprived populations. The location of socioeconomically deprived immigrants is important for the development of public policy intelligence at the local and national levels but their areas of residence have not been mapped in Chile. This study explored the spatial distribution of socioeconomic deprivation among immigrants in Chile, 1992–2012, and compared it to the total population.

Material and Methods

Areas with socioeconomically deprived populations were identified with a deprivation index which we developed modelled upon the Index of Multiple Deprivation (IMD) for England. Our IMD was based upon the indicators of unemployment, low educational level (primary) and disability from Census data at county level for the three decades 1992, 2002 and 2012, for 332, 339 and 343 counties respectively. We developed two versions of the IMD one based on disadvantage among the total population and another focused upon the circumstances of immigrants only. We generated a spatial representation of the IMD using GIS, for the overall IMD score and for each dimension of the index, separately. We also compared the immigrants´ IMD to the total population´s IMD using Pearson´s correlation test.

Results

Results showed that socioeconomically deprived immigrants tended to be concentrated in counties in the northern and central area of Chile, in particular within the Metropolitan Region of Santiago. These were the same counties where there was the greatest concentration of socioeconomic deprivation for the total population during the same time periods. Since 1992 there have been significant change in the location of the socioeconomically deprived populations within the Metropolitan Region of Santiago with the highest IMD scores for both the total population and immigrants becoming increasingly concentrated in the central and eastern counties of the Region.

Conclusion

This is the first study analysing the spatial distribution of socioeconomic deprivation among international immigrants and the total population in a Latin American country. Findings could inform policy makers about location of areas of higher need of social protection in Chile, for both immigrants and the total resident population in the country.     

A new methodology combining PCR, cloning, and sequencing of clones discriminated by RFLP for the study of microbial populations: application to an UASB reactor sample

This work describes a methodology combining DNA extraction, polymerase chain reaction amplification with primers targeting 16S ribosomal RNA genes, cloning, and sequencing of clones previously analyzed by restriction fragment length polymorphism (RFLP), which can be applied to study the microbial diversity in a given habitat. The methodology allows the minimization of the sequencing effort, which is particularly relevant when analyzing large numbers of clones. The methodology does not require particularly skilled personnel and can easily be adaptable to the molecular characterization of virtually any particular microbial population, provided that both adequate primers and suitable restriction enzymes for RFLP analysis of the clone library have been chosen. An example of application is presented, in which a sample taken from a continuously operating upflow anaerobic sludge blanket reactor was analyzed. RFLP analysis of the initial 162 clones with HaeIII allowed the identification of only 28 distinct profiles. As expected, identical RFLP profiles corresponded to identical nucleotide sequences.     

The calcium-binding C-terminal domain of Escherichia coli alpha-hemolysin is a major determinant in the surface-active properties of the protein

alpha-Hemolysin (HlyA) from Escherichia coli is a protein toxin (1024 amino acids) that targets eukaryotic cell membranes, causing loss of the permeability barrier. HlyA consists of two main regions, an N-terminal domain rich in amphipathic helices, and a C-terminal Ca(2+)-binding domain containing a Gly- and Asp-rich nonapeptide repeated in tandem 11-17 times. The latter is called the RTX domain and gives its name to the RTX protein family. It had been commonly assumed that membrane interaction occurred mainly if not exclusively through the amphipathic helix domain. However, we have cloned and expressed the C-terminal region of HlyA, containing the RTX domain plus a few stabilizing sequences, and found that it is a potent surface-active molecule. The isolated domain binds Ca(2+) with about the same affinity (apparent K(0.5) approximately 150 microM) as the parent protein HlyA, and Ca(2+) binding induces in turn a more compact folding with an increased proportion of beta-sheet structure. Both with and without Ca(2+) the C-terminal region of HlyA can interact with lipid monolayers spread at an air-water interface. However, the C-terminal domain by itself is devoid of membrane lytic properties. The present results can be interpreted in the light of our previous studies that involved in receptor binding a peptide in the C-terminal region of HlyA. We had also shown experimentally the distinction between reversible membrane adsorption and irreversible lytic insertion of the toxin. In this context, the present data allow us to propose that both major domains of HlyA are directly involved in membrane-toxin interaction, the nonapeptide repeat, calcium-binding RTX domain being responsible for the early stages of HlyA docking to the target membrane.     

RTN4B interacting protein FAM134C promotes ER membrane curvature and has a functional role in autophagy

The endoplasmic reticulum (ER) is composed of a controlled ratio of sheets and tubules, which are maintained by several proteins with multiple functions. Reticulons (RTNs), especially RTN4, and DP1/Yop1p family members are known to induce ER membrane curvature. RTN4B is the main RTN4 isoform expressed in nonneuronal cells. In this study, we identified FAM134C as a RTN4B interacting protein in mammalian, nonneuronal cells. FAM134C localized specifically to the ER tubules and sheet edges. Ultrastructural analysis revealed that overexpression of FAM134C induced the formation of unbranched, long tubules or dense globular structures composed of heavily branched narrow tubules. In both cases, tubules were nonmotile. ER tubulation was dependent on the reticulon homology domain (RHD) close to the N-terminus. FAM134C plays a role in the autophagy pathway as its level elevated significantly upon amino acid starvation but not during ER stress. Moreover, FAM134C depletion reduced the number and size of autophagic structures and the amount of ER as a cargo within autophagic structures under starvation conditions. Dominant-negative expression of FAM134C forms with mutated RHD or LC3 interacting region also led to a reduced number of autophagic structures. Our results suggest that FAM134C provides a link between regulation of ER architecture and ER turnover by promoting ER tubulation required for subsequent ER fragmentation and engulfment into autophagosomes.     

Screening of a Leptospira biflexa Mutant Library To Identify Genes Involved in Ethidium Bromide Tolerance

Leptospira spp. are spirochete bacteria comprising both pathogenic and free-living species. The saprophyte L. biflexa is a model bacterium for studying leptospiral biology due to relative ease of culturing and genetic manipulation. In this study, we constructed a library of 4,996 random transposon mutants in L. biflexa. We screened the library for increased susceptibility to the DNA intercalating agent, ethidium bromide (EtBr), in order to identify genetic determinants that reduce L. biflexa susceptibility to antimicrobial agents. By phenotypic screening, using subinhibitory EtBr concentrations, we identified 29 genes that, when disrupted via transposon insertion, led to increased sensitivity of the bacteria to EtBr. At the functional level, these genes could be categorized by function as follows: regulation and signaling (n = 11), transport (n = 6), membrane structure (n = 5), stress response (n = 2), DNA damage repair (n = 1), and other processes (n = 3), while 1 gene had no predicted function. Genes involved in transport (including efflux pumps) and regulation (two-component systems, anti-sigma factor antagonists, etc.) were overrepresented, demonstrating that these genes are major contributors to EtBr tolerance. This finding suggests that transport genes which would prevent EtBr to enter the cell cytoplasm are critical for EtBr resistance. We identified genes required for the growth of L. biflexa in the presence of sublethal EtBr concentration and characterized their potential as antibiotic resistance determinants. This study will help to delineate mechanisms of adaptation to toxic compounds, as well as potential mechanisms of antibiotic resistance development in pathogenic L. interrogans.     

Protein Tyrosine Phosphatase-PEST and β8 Integrin Regulate Spatiotemporal Patterns of RhoGDI1 Activation in Migrating Cells

Directional cell motility is essential for normal development and physiology, although how motile cells spatiotemporally activate signaling events remains largely unknown. Here, we have characterized an adhesion and signaling unit comprised of protein tyrosine phosphatase (PTP)-PEST and the extracellular matrix (ECM) adhesion receptor β8 integrin that plays essential roles in directional cell motility. β8 integrin and PTP-PEST form protein complexes at the leading edge of migrating cells and balance patterns of Rac1 and Cdc42 signaling by controlling the subcellular localization and phosphorylation status of Rho GDP dissociation inhibitor 1 (RhoGDI1). Translocation of Src-phosphorylated RhoGDI1 to the cell''s leading edge promotes local activation of Rac1 and Cdc42, whereas dephosphorylation of RhoGDI1 by integrin-bound PTP-PEST promotes RhoGDI1 release from the membrane and sequestration of inactive Rac1/Cdc42 in the cytoplasm. Collectively, these data reveal a finely tuned regulatory mechanism for controlling signaling events at the leading edge of directionally migrating cells.