How do bacteria sense and respond to low temperature?

Rigidification of the membrane appears to be the primary signal perceived by a bacterium when exposed to low temperature. The perception and transduction of the signal then occurs through a two-component signal transduction pathway consisting of a membrane-associated sensor and a cytoplasmic response regulator and as a consequence a set of cold-regulated genes are activated. In addition, changes in DNA topology due to change in temperature may also trigger cold-responsive mechanisms. Inducible proteins thus accumulated repair the damage caused by cold stress. For example, the fluidity of the rigidified membrane is restored by altering the levels of saturated and unsaturated fatty acids, by altering the fatty acid chain length, by changing the proportion of cis to trans fatty acids and by changing the proportion of anteiso to iso fatty acids. Bacteria could also achieve membrane fluidity changes by altering the protein content of the membrane and by altering the levels of the type of carotenoids synthesized. Changes in RNA secondary structure, changes in translation and alteration in protein conformation could also act as temperature sensors. This review highlights the various strategies by which bacteria senses low temperature signal and as to how it responds to the change.     

How do sinking phytoplankton species manage to persist?

Phytoplankton require light for photosynthesis. Yet, most phytoplankton species are heavier than water and therefore sink. How can these sinking species persist? Somehow, the answer should lie in the turbulent motion that redisperses sinking phytoplankton over the vertical water column. Here, we show, using a reaction-advection-diffusion equation of light-limited phytoplankton, that there is a turbulence window sustaining sinking phytoplankton species in deep waters. If turbulent diffusion is too high, phytoplankton are mixed to great depths, and the depth-averaged light conditions are too low to allow net positive population growth. Conversely, if turbulent diffusion is too low, sinking phytoplankton populations end up at the ocean floor and succumb in the dark. At intermediate levels of turbulent diffusion, however, phytoplankton populations can outgrow both mixing rates and sinking rates. In this way, the reproducing population as a whole can maintain a position in the well-lit zone near the top of the water column, even if all individuals within the population have a tendency to sink. This theory unites earlier classic results by Sverdrup and Riley as well as our own recent findings and provides a new conceptual framework for the understanding of phytoplankton dynamics under the influence of mixing processes.     

How do sex and sexual maturation influence the response of Monochamus galloprovincialis to host odours?

Finding the right host plant for feeding and reproduction is crucial for herbivorous insects. Usually they need both visual and olfactory cues to locate and colonize their host plants, but the respective role of the two types of stimuli is difficult to disentangle. Model plants mimicking the shape and colour of natural hosts, combined with odours dispensers, are relevant tools for this purpose. We used dummy pines and cut branches of natural pines to investigate host attraction in Monochamus galloprovincialis, the insect vector of the pine wood nematode in Europe. We compared the behavioural response of males and females, sexually mature or immature, in a large climatic chamber and in an olfactometer. Immature females were significantly attracted by the sole odours released by pines. Immature males and mature males and females needed a combination of visual and olfactory cues to find the host tree. These findings suggest that beetles use both visual and chemical cues to locate pine trees but that relevant stimuli likely differ between beetles of different sex and sexual maturation status. Our results question the implementation of precautionary clear‐cuts around infested trees for limiting the spread of PWN.     

How do tenascins influence the birth and life of a malignant cell?

Tenascins are large glycoproteins found in embryonic and adult extracellular matrices. Of the four family members, two have been shown to be overexpressed in the microenvironment of solid tumours: tenascin-C and tenascin-W. The regular presence of these proteins in tumours suggests a role in tumourigenesis, which has been investigated intensively for tenascin-C and recently for tenascin-W as well. In this review, we follow a malignant cell starting from its birth through its potential metastatic journey and describe how tenascin-C and tenascin-W contribute to these successive steps of tumourigenesis. We consider the importance of the mechanical aspect in tenascin signalling. Furthermore, we discuss studies describing tenascin-C as an important component of stem cell niches and present examples reporting its role in cancer therapy resistance.     

How do surfactants and DTT affect the size, dynamics, activity and growth of soluble lysozyme aggregates?

The early intermediates in the protein aggregation pathway, the elusive soluble aggregates, play a pivotal role in growth and maturation of ordered aggregates such as amyloid fibrils. Blocking the growth of soluble oligomers is an effective strategy to inhibit aggregation. To decipher the molecular mechanisms and develop better strategies to arrest aggregation, it is imperative to understand how the size, molecular dynamics, activity and growth kinetics of soluble aggregates are affected when aggregation is inhibited. With this objective, in the present study we have investigated the influence of additives such as SDS, CTAB (cetyltrimethylammonium bromide) and DTT (dithiothreitol) on the slow aggregation of HEWL (hen eggwhite lysozyme) at pH 12.2. For this purpose, techniques such as steady-state and time-resolved fluorescence anisotropy of covalently labelled dansyl probe, gel-filtration chromatography, estimation of free thiol groups, thioflavin T and ANS (8-anilinonaphthalene-1-sulfonic acid) fluorescence, CD and atomic-force microscopy were employed to monitor the soluble oligomers over a period spanning 30 days. The results of the present study reveal that: (i) the spontaneous formation of soluble aggregates is irreversible and abolishes activity; (ii) the initial growth of aggregates (0-24 h) is promoted by a gradual increase in the exposure of hydrophobic surfaces; (iii) subsequently intermolecular disulfide bonds are critical for the assembly and stability of aggregates; (iv) the tight molecular packing inside large aggregates which contributed to slow (approximately 5 ns) and restricted segmental motion of dansyl probe was clearly loosened up in the presence of additives, enabling fast (1-2 ns) and free motion (unlike DTT, the size of lysozyme complexes with surfactants, was large, due to a conglomeration of proteins and surfactants); (v) the aggregates show reduced helical content compared with native lysozyme, except in the presence of SDS; and (vi) DTT was more potent than SDS/CTAB in arresting the growth of aggregates.     

How do drought and fire influence the patterns of resprouting in Australian deserts?

Rainfall is the key driver of woody cover and life-history attributes in arid grassy biomes where disturbance is mostly rare and of low intensity. However, relatively little is known about the causes of woody community assembly in arid systems that are subject to periodic intense fire disturbance. In the central Australian desert region, grassland and shrubland fire can occur following above average rainfall. Patterns of species regeneration response (resprouting vs. reseeding) are poorly documented in this region. We tested the effects of rainfall and fire on species’ resprouting response across the latitudinal rainfall–fire gradient using constrained ordination of 385 sites and general linear models. A resprouting response was significantly greater in grassland habitat as well as at the high end of the rainfall–fire gradient. The frequency of epicormic stem resprouting also increased along the rainfall–fire gradient. We attribute this pattern to the combined effects of frequent fire and rapid gap closure on seedlings of slow-growing, fire-killed woody species in higher rainfall grasslands. In addition, we also demonstrated that rapidly maturing fire-recruiting species are similarly favoured by high fire disturbance. In arid grassy ecosystems, unlike in mesic savanna, flammable grassland supports a mix of resprouting and recruitment functional types, and habitat membership cannot be predicted by resprouting capacity. Regions, such as central Australia, that are characterised by grassland–shrubland mosaics of high and low fuel biomass, respectively, pose specific challenges to fire ecology research that are possibly best dealt with by focussing modelling at the habitat scale.     

How do social dominance and social information influence reproduction and the brain?

How does living in a social environment influence the brain? In particular, we ask the following questions: How do animals perceive and use social information? How does the perception of social information influence the reproductive system? Where is this represented in the brain? We present a model system in which these questions can be addressed, focusing on the brain's role in integrating information. In the social fish, Astatotilapia burtoni (Haplochromis), the relationship between social status and gonadotropin-releasing hormone (GnRH1) has been well established. Change in status results in numerous changes in the physiology of A. burtoni at every level of organization. Social status can regulate reproduction via the hypothalamic-pituitary-gonadal (HPG) axis. GnRH1 is used by the brain to signal the pituitary about reproductive state so reproductive control depends on regulation of this signaling peptide. In this fish, social dominance is tightly coupled to fertility. Here, we have exploited this link to understand the regulatory systems from circulating hormones, brain volume to gene expression.     

UV radiation: what we know and do we protect ourselves adequately?

Chronic sun exposure causes degenerative changes in the skin that are recognized as photoaging, immunosuppression and photocarcinogenesis. Sun is necessary for life, so total sun avoidance is impossible. Sun exposure during the first 15 years of life and blistering sunburns before age 20 have been linked to an increased risk of melanoma. Individuals who have outdoor lifestyles, live in sunny climates, and are lightly pigmented will experience the greatest degree of photoaging. In our study, performed four years ago, we have shown the knowledge of more than 4000 people about the effects of UV rays on the skin. The results show us that sun exposure is still exaggerated and uncontrolled due to the lack of knowledge about this topic. Encouraging photoprotection and improving the awareness of the general public about the harmful effects of too much sun exposure must be the leading preventative health strategy.     

Are the conformational dynamics and the ligand binding properties of myoglobin affected by exposure to microwave radiation?

The global uptake of mobile communication emphasizes the question about possible adverse consequences of the exposure to low-level radiofrequency radiation from mobile phones on human health as result of so-called "non-thermal effects". In order to state safety guidelines it seems appropriate to start by excluding, if possible, non-specific effects on structural and dynamic properties of fundamental biomolecules such as proteins. Proteins are flexible polyelectrolytes; thus, they are susceptible, in principle, to the action of electromagnetic fields. In this article, we investigated the effects of microwaves on structural and functional properties of Tunnus tynnus myoglobin at 1.95 GHz, a frequency used by new wireless microwave communication systems. The protein solution was exposed for 2.5 h to 51 mW/g SAR (specific absorption rate) level. Measurements of absorption spectroscopy, circular dichroism and fluorescence emission decay in the frequency domain do not exhibit any influence of the radiation on the native structural state of protein macromolecules.     

How well do laboratory experiments explain field patterns of zooplankton emergence?

1. We conducted a laboratory experiment to explore potential mechanisms driving variation in zooplankton emergence from diapausing eggs observed in Oneida Lake, NY, U.S.A. We hypothesized that variation in timing of ice-out (date of thawing of ice) between 1994 and 1995, which resulted in variation in photoperiod–temperature cues, contributed to the differences in the observed field patterns. Environmental chambers were used to establish weekly photoperiod–temperature combinations that reproduced natural conditions in Oneida Lake in 1994 and 1995. In addition, a third treatment ('dark') exposed eggs only to the changes in temperature. We recorded zooplankton emergence for 2.5 simulated ice-free seasons.
2. Nine cladoceran taxa were found to hatch, but only Daphnia pulicaria in large numbers. Hatching of D. pulicaria was recorded throughout the season in the two light treatments and sporadically in the dark treatment. The early ice-out treatment had the highest emergence, followed by the late ice-out and dark treatments. Among taxa, there was temporal segregation with five hatching in the early weeks of sampling and two taxa hatching during the middle weeks. Alona hatched late in the first year, but earlier in the second year.
3. We compared our laboratory results of D. pulicaria hatching with the field data obtained by Cáceres (1998) . Hatching was continuous in the laboratory, whereas a synchronous spring emergence was found in the field. However, in both the laboratory and the field, more D. pulicaria hatched under conditions reflecting ice-out occurring in March as opposed to April. Because differences in rates and timing of emergence can affect the population and community dynamics of pelagic systems, we suggest caution when applying laboratory results to field populations.     

How do Bax and Bak lead to permeabilization of the outer mitochondrial membrane?

Bcl-2 family members, like the structurally similar translocation domain of diphtheria toxin, can form ion-selective channels and larger-diameter pores in artificial lipid bilayers. Recent studies show how Bcl-2 family members change topology in membranes during apoptosis and that these different states may either promote or inhibit apoptosis. Binding of BH3-only proteins alters the subcellular localization and/or membrane topology and probably affects the channel formation of Bcl-2, Bcl-xL and Bcl-w. However, it remains unclear how the pore-forming activity functions in cells to regulate mitochondrial membrane permeabilization and cell death. Bcl-2 family members in flies and worms regulate apoptosis by mechanisms seemingly unrelated to membrane permeabilization, leaving a unifying model for the biochemical activity of this protein family unknown. Work linking Bcl-2 family members to mitochondrial morphogenesis in worms and mammals suggests some common functions of Bcl-2 family proteins may exist.     

Diversity measures in macroinvertebrate and zooplankton communities related to the trophic status of subtropical reservoirs: Contradictory or complementary responses?

Macroinvertebrate communities have been widely used as a tool for assessing the environmental quality of freshwater ecosystems, whereas zooplankton communities have been to some extent neglected. However, the importance of using different indicators to achieve a more comprehensive framework of assessment regarding water quality has been recognized. This study compared estimates of species richness (number of species) and the Shannon–Wiener index for data on macroinvertebrate and zooplankton communities in tropical reservoirs and related them to their trophic state. The trop+hic classification was obtained by applying the Carlson index (1977) modified by Toledo et al. (1983), and the index of the Brazilian Society of the Environmental Technology Agency. The comparative response of the different indicators was analyzed using a series of bivariate correlations (Draftsman’s plot). The results illustrate that diversity measures, namely species richness, responded differently when related to the trophic classification of reservoirs, depending on the community considered. The species richness of zooplankton was positively related to hypereutrophic conditions, due to the higher number of rotifer species, including tolerant generalist species and at the same time, as a result of the exclusion of species from other groups, whereas for macroinvertebrates, species richness was negatively related to hypereutrophic conditions. Melanoides tuberculatus, which exhibits a high tolerance and competitive ability under such conditions, was the dominant species in macroinvertebrate communities, which excluded endemic species and reduced local richness and diversity. The same indicators applied to the zooplankton and macroinvertebrate communities might therefore provide contradictory responses regarding ecological quality assessment in tropical reservoirs, which suggest that zooplankton should be taken into account among the biological quality elements considered in the ecological quality assessment, management, and restoration of water bodies.     

How past and present influence the foraging of clonal plants?

Clonal plants spreading horizontally and forming a network structure of ramets exhibit complex growth patterns to maximize resource uptake from the environment. They respond to spatial heterogeneity by changing their internode length or branching frequency. Ramets definitively root in the soil but stay interconnected for a varying period of time thus allowing an exchange of spatial and temporal information. We quantified the foraging response of clonal plants depending on the local soil quality sampled by the rooting ramet (i.e. the present information) and the resource variability sampled by the older ramets (i.e. the past information). We demonstrated that two related species, Potentilla reptans and P. anserina, responded similarly to the local quality of their environment by decreasing their internode length in response to nutrient-rich soil. Only P. reptans responded to resource variability by decreasing its internode length. In both species, the experience acquired by older ramets influenced the plastic response of new rooted ramets: the internode length between ramets depended not only on the soil quality locally sampled but also on the soil quality previously sampled by older ramets. We quantified the effect of the information perceived at different time and space on the foraging behavior of clonal plants by showing a non-linear response of the ramet rooting in the soil of a given quality. These data suggest that the decision to grow a stolon or to root a ramet at a given distance from the older ramet results from the integration of the past and present information about the richness and the variability of the environment.     

How well do reduced models capture the dynamics in models of interacting neurons?

This paper introduces a class of stochastic models of interacting neurons with emergent dynamics similar to those seen in local cortical populations. Rigorous results on existence and uniqueness of nonequilibrium steady states are proved. These network models are then compared to very simple reduced models driven by the same mean excitatory and inhibitory currents. Discrepancies in firing rates between network and reduced models are investigated and explained by correlations in spiking, or partial synchronization, working in concert with “nonlinearities” in the time evolution of membrane potentials. The use of simple random walks and their first passage times to simulate fluctuations in neuronal membrane potentials and interspike times is also considered.