Peptidoglycan synthesis drives an FtsZ-treadmilling-independent step of cytokinesis.

Peptidoglycan is the main component of the bacterial wall and protects cells from the mechanical stress that results from high intracellular turgor. Peptidoglycan biosynthesis is very similar in all bacteria; bacterial shapes are therefore mainly determined by the spatial and temporal regulation of peptidoglycan synthesis rather than by the chemical composition of peptidoglycan. The form of rod-shaped bacteria, such as Bacillus subtilis or Escherichia coli, is generated by the action of two peptidoglycan synthesis machineries that act at the septum and at the lateral wall in processes coordinated by the cytoskeletal proteins FtsZ and MreB, respectively. The tubulin homologue FtsZ is the first protein recruited to the division site, where it assembles in filaments-forming the Z ring-that undergo treadmilling and recruit later divisome proteins. The rate of treadmilling in B. subtilis controls the rates of both peptidoglycan synthesis and cell division. The actin homologue MreB forms discrete patches that move circumferentially around the cell in tracks perpendicular to the long axis of the cell, and organize the insertion of new cell wall during elongation. Cocci such as Staphylococcus aureus possess only one type of peptidoglycan synthesis machinery, which is diverted from the cell periphery to the septum in preparation for division. The molecular cue that coordinates this transition has remained elusive. Here we investigate the localization of S. aureus peptidoglycan biosynthesis proteins and show that the recruitment of the putative lipid II flippase MurJ to the septum, by the DivIB-DivIC-FtsL complex, drives peptidoglycan incorporation to the midcell. MurJ recruitment corresponds to a turning point in cytokinesis, which is slow and dependent on FtsZ treadmilling before MurJ arrival but becomes faster and independent of FtsZ treadmilling after peptidoglycan synthesis activity is directed to the septum, where it provides additional force for cell envelope constriction.

Mycobacterium leprae diversity and population dynamics in medieval Europe from novel ancient genomes.

BACKGROUND: Hansen's disease (leprosy), widespread in medieval Europe, is today mainly prevalent in tropical and subtropical regions with around 200,000 new cases reported annually. Despite its long history and appearance in historical records, its origins and past dissemination patterns are still widely unknown. Applying ancient DNA approaches to its major causative agent, Mycobacterium leprae, can significantly improve our understanding of the disease's complex history. Previous studies have identified a high genetic continuity of the pathogen over the last 1500 years and the existence of at least four M. leprae lineages in some parts of Europe since the Early Medieval period. RESULTS: Here, we reconstructed 19 ancient M. leprae genomes to further investigate M. leprae's genetic variation in Europe, with a dedicated focus on bacterial genomes from previously unstudied regions (Belarus, Iberia, Russia, Scotland), from multiple sites in a single region (Cambridgeshire, England), and from two Iberian leprosaria. Overall, our data confirm the existence of similar phylogeographic patterns across Europe, including high diversity in leprosaria. Further, we identified a new genotype in Belarus. By doubling the number of complete ancient M. leprae genomes, our results improve our knowledge of the past phylogeography of M. leprae and reveal a particularly high M. leprae diversity in European medieval leprosaria. CONCLUSIONS: Our findings allow us to detect similar patterns of strain diversity across Europe with branch 3 as the most common branch and the leprosaria as centers for high diversity. The higher resolution of our phylogeny tree also refined our understanding of the interspecies transfer between red squirrels and humans pointing to a late antique/early medieval transmission. Furthermore, with our new estimates on the past population diversity of M. leprae, we gained first insights into the disease's global history in relation to major historic events such as the Roman expansion or the beginning of the regular transatlantic long distance trade. In summary, our findings highlight how studying ancient M. leprae genomes worldwide improves our understanding of leprosy's global history and can contribute to current models of M. leprae's worldwide dissemination, including interspecies transmissions.

Chemosteometric regression models of heat exposed human bones to determine their pre-burnt metric dimensions.

OBJECTIVES: Heat exposure can lead to apparently random osteometric changes that hinder the application of metric methods used for biological profiling. The impracticality of using objective and burn-specific osteometric methods reduces the chances of establishing the biological profiles of unknown individuals based on their skeletal remains. We investigated the potential of chemometry analysis based on infrared spectroscopy to predict the amount of heat-induced osteometric changes and how this reflected into sex estimation. MATERIAL AND METHODS: Bones from 41 identified adult skeletons (24 females and 17 males with ages between 62 and 90 years old) were experimentally burnt to maximum temperatures ranging from 450°C to 1,100°C (attained after 65 to 240 min). Measurements were taken both before and after each experiment and powder samples were analyzed through FTIR-ATR. Correlations among heat-induced metric changes and chemometric indices (crystallinity index; B-type carbonates; carbonate [A + B] to carbonate B ratio; hydroxyl to phosphate ratio; 630 cm-1 , 1450 cm-1 , 3572 cm-1 , and 3642 cm-1 ) were tested. Significant variables were used to build regression models to predict heat-induced metric change which were then tested on an independent set of samples. Agreement in sex estimation between the pre- and post-burnt samples was also evaluated. RESULTS: All indices were significantly correlated to heat-induced metric changes (α = .01) and the highest correlations were obtained for the 630 cm-1 , 3572 cm-1 , and crystallinity index. We confirmed that regression models based on chemometrics obtained from infrared spectra through FTIR-ATR are better at estimating heat-induced metric changes affecting bone and at sexing remains than other osteometric methods such as those based on correction factors or on metric references specific to calcined bones. DISCUSSION: Regression models avoid the subjectivity associated with the application of other methods. While the latter can be applied only to calcined bones, which is difficult to assess sometimes, regression models can be applied to all bones regardless of their condition. Also, regression models have the advantage of allowing to infer about heat-induced metric change on a case-by-case basis.

Cryptotermes brevis (Isoptera: Kalotermitidae) in the Azores: lessons after 2 yr of monitoring in the Archipelago.

The dispersal flights of West Indian drywood termite, Cryptotermes brevis (Walker) (Isoptera: Kalotermitidae) were surveyed in the major cities of Azores. The sampling device used to estimate termite density consisted of a yellow adhesive trap (size 45 by 24 cm), placed with an artificial or natural light source in a dark attic environment. In addition, data from two other projects were used to improve the knowledge about the geographical distribution of the species. The level of infestation in the two main Azorean towns differed, with high levels in the houses of Angra do Heroísmo, whereas in Ponta Delgada, there are fewer houses with high levels of infestation. The infestation in Ponta Delgada shows a pattern of spreading from the center outward to the city's periphery, whereas in Angra do Heroísmo, there was a pattern of spreading outward from several foci. The heavy infestation observed in Angra do Heroísmo and the clear increase of infestation levels observed from 2010 to 2011 is a reason for concern and calls for an urgent application of an Integrated Pest Management (IPM) control strategy.

The ADnet Bayesian belief network for alder decline: Integrating empirical data and expert knowledge.

The globalization in plant material trading has caused the emergence of invasive pests in many ecosystems, such as the alder pathogen Phytophthora ×alni in European riparian forests. Due to the ecological importance of alder to the functioning of rivers and the increasing incidence of P. ×alni-induced alder decline, effective and accessible decision tools are required to help managers and stakeholders control the disease. This study proposes a Bayesian belief network methodology to integrate diverse information on the factors affecting the survival and infection ability of P. ×alni in riparian habitats to help predict and manage disease incidence. The resulting Alder Decline Network (ADnet) management tool integrates information about alder decline from scientific literature, expert knowledge and empirical data. Expert knowledge was gathered through elicitation techniques that included 19 experts from 12 institutions and 8 countries. An original dataset was created covering 1189 European locations, from which P. ×alni occurrence was modeled based on bioclimatic variables. ADnet uncertainty was evaluated through its sensitivity to changes in states and three scenario analyses. The ADnet tool indicated that mild temperatures and high precipitation are key factors favoring pathogen survival. Flood timing, water velocity, and soil type have the strongest influence on disease incidence. ADnet can support ecosystem management decisions and knowledge transfer to address P. ×alni-induced alder decline at local or regional levels across Europe. Management actions such as avoiding the planting of potentially infected trees or removing man-made structures that increase the flooding period in disease-affected sites could decrease the incidence of alder disease in riparian forests and limit its spread. The coverage of the ADnet tool can be expanded by updating data on the pathogen's occurrence, particularly from its distributional limits. Research on the role of genetic variability in alder susceptibility and pathogen virulence may also help improve future ADnet versions.

Do small barriers affect the movement of freshwater fish by increasing residency?

River fragmentation due to artificial barriers directly impacts fish communities by limiting migratory movements. This work aims to understand how small barriers affect the movements of a potamodromous cyprinid species - the Iberian barbel (Luciobarbus bocagei (Steindachner, 1864)) - in a 5.6km upstream segment of a stream impacted only by the presence of physical barriers. Fish were marked with Visible Implant Elastomer tags (VIE), and barriers were seasonally characterized. A total of 683 fish were tagged, with 104 recaptures, during five sampling seasons (spring 2012 - early summer 2013). Eleven of the recaptured fish moved past a barrier, without any preference in terms of direction of movement. There were no differences in length, either between migrants and residents, or between upstream and downstream migrants. The results show that although barbel are able to negotiate small barriers, part of the population did not move between fragmented reaches - an indication that under such conditions, fish species populations may adjust their life-history strategy to augment residency as it was hypothesized from the results.

Potamodromous fish movements under multiple stressors: Connectivity reduction and oxygen depletion.

Rivers are impacted by multiple stressors that can interact to create synergistic, additive or antagonistic effects, but experimental studies on fish encompassing more than one stressor are seldom found. Thus, there is the need to study stressors through multifactorial approaches that analyse the impact of fish exposure to multiple stressors and evaluate fish sensitivity to stressor combinations. Some of the most common impacts to Mediterranean rivers are of two natures: i) water abstraction and ii) diffuse pollution. Therefore, the present study aims at studying the responses of potamodromous fish facing combinations of: 1) a primary stressor (two levels of connectivity reduction due to water scarcity), and 2) a secondary stressor (three levels of oxygen depletion due to increase organic load - of anthropogenic nature). Schools of five wild fish from a cyprinid species (Luciobarbus bocagei) were placed in a flume, equipped with see-through sidewalls to allow for behavioural analysis, and subjected to different combinations of the stressors. Results show that at the unconnected level the primary stressor (lack of connectivity) overrode the effect of the secondary stressor (oxygen depletion), but when connectivity existed oxygen depletion caused a reduction of fish movements with decreasing oxygen concentrations. This multifactorial study contributes to improved prediction of fish responses upon actual or projected pressure scenarios.

Cell shape dynamics during the staphylococcal cell cycle.

Staphylococcus aureus is an aggressive pathogen and a model organism to study cell division in sequential orthogonal planes in spherical bacteria. However, the small size of staphylococcal cells has impaired analysis of changes in morphology during the cell cycle. Here we use super-resolution microscopy and determine that S. aureus cells are not spherical throughout the cell cycle, but elongate during specific time windows, through peptidoglycan synthesis and remodelling. Both peptidoglycan hydrolysis and turgor pressure are required during division for reshaping the flat division septum into a curved surface. In this process, the septum generates less than one hemisphere of each daughter cell, a trait we show is common to other cocci. Therefore, cell surface scars of previous divisions do not divide the cells in quadrants, generating asymmetry in the daughter cells. Our results introduce a need to reassess the models for division plane selection in cocci.

Pool-type fishways: two different morpho-ecological cyprinid species facing plunging and streaming flows.

Fish are particularly sensitive to connectivity loss as their ability to reach spawning grounds is seriously affected. The most common way to circumvent a barrier to longitudinal connectivity, and to mitigate its impacts, is to implement a fish passage device. However, these structures are often non-effective for species with different morphological and ecological characteristics so there is a need to determine optimum dimensioning values and hydraulic parameters. The aim of this work is to study the behaviour and performance of two species with different ecological characteristics (Iberian barbel Luciobarbus bocagei-bottom oriented, and Iberian chub Squalius pyrenaicus-water column) in a full-scale experimental pool-type fishway that offers two different flow regimes-plunging and streaming. Results showed that both species passed through the surface notch more readily during streaming flow than during plunging flow. The surface oriented species used the surface notch more readily in streaming flow, and both species were more successful in moving upstream in streaming flow than in plunging flow. Streaming flow enhances upstream movement of both species, and seems the most suitable for fishways in river systems where a wide range of fish morpho-ecological traits are found.

Modelling stream-fish functional traits in reference conditions: regional and local environmental correlates.

Identifying the environmental gradients that control the functional structure of biological assemblages in reference conditions is fundamental to help river management and predict the consequences of anthropogenic stressors. Fish metrics (density of ecological guilds, and species richness) from 117 least disturbed stream reaches in several western Iberia river basins were modelled with generalized linear models in order to investigate the importance of regional- and local-scale abiotic gradients to variation in functional structure of fish assemblages. Functional patterns were primarily associated with regional features, such as catchment elevation and slope, rainfall, and drainage area. Spatial variations of fish guilds were thus associated with broad geographic gradients, showing (1) pronounced latitudinal patterns, affected mainly by climatic factors and topography, or (2) at the basin level, strong upstream-downstream patterns related to stream position in the longitudinal gradient. Maximum native species richness was observed in midsize streams in accordance with the river continuum concept. The findings of our study emphasized the need to use a multi-scale approach in order to fully assess the factors that govern the functional organization of biotic assemblages in 'natural' streams, as well as to improve biomonitoring and restoration of fluvial ecosystems.