YopT, a new Yersinia Yop effector protein, affects the cytoskeleton of host cells

Extracellular Yersinia disarm the immune system of their host by injecting effector Yop proteins into the cytosol of target cells. Five effectors have been described: YopE, YopH, YpkA/YopO, YopP and YopM. Delivery of these effectors by Yersinia adhering at the cell surface requires other Yops (translocators) including YopB. Effector and translocator Yops are secreted by the type III Ysc secretion apparatus, and some Yops also need a specific cytosolic chaperone, called Syc. In this paper, we describe a new Yop, which we have called YopT (35.5 kDa). Its secretion required an intact Ysc apparatus and SycT (15.0 kDa, pI 4.4), a new chaperone resembling SycE. Infection of macrophages with a Yersinia , producing a hybrid YopT–adenylate cyclase, led to the accumulation of intracellular cAMP, indicating that YopT is delivered into the cytosol of eukaryotic cells. Infection of HeLa cells with a mutant strain devoid of the five known Yop effectors (ΔHOPEM strain) but producing YopT resulted in the alteration of the cell cytoskeleton and the disruption of the actin filament structure. This cytotoxic effect was caused by YopT and dependent on YopB. YopT is thus a new effector Yop and a new bacterial toxin affecting the cytoskeleton of eukaryotic cells.     

Habitat selection,diet and food availability of European Golden Plover Pluvialis apricaria chicks in Swedish Lapland

Fennoscandian alpine tundra habitats support large numbers of breeding waders, but relatively little is known about their breeding ecology despite the fact that this habitat is threatened by climate change. We studied habitat selection, diet and prey availability of European (Eurasian) Golden Plover Pluvialis apricaria chicks at the Vindelfjällen Nature Reserve, Ammarnäs, Sweden. Information from 22 chicks tracked using radio‐transmitters was analysed. By analysing 149 faecal samples, four main prey taxa were identified, Coleoptera (40%), Bibionidae (31%), Hymenoptera (13%) and Tipulidae (10%). We found that chicks switched from feeding on Tipulidae to feeding on Bibionidae as they grew, and that this switch coincided with a shift from the use of the habitat where Tipulidae were abundant (alpine meadow/heathland) to the use of the habitat were Bibionidae were abundant (Willow shrub). Although chicks track food availability to some extent, the link between prey availability and habitat use was not perfect, indicating that additional factors other than food abundance, such as shelter from predators, determine habitat selection. Bibionidae are an important prey for Golden Plover chicks as it is the only prey group that has a late summer flush in abundance, in contrast to the general decline of total arthropod biomass during the chick‐rearing period. However, Bibionidae imagoes only occurred in 2011 and were virtually absent in 2013, which relates to the species’ ecology with 2‐ to 5‐year cycles in mass occurrence. Extreme annual variation in an essential food source such as Bibionidae imagoes might have an important effect on the condition and survival of Golden Plover chicks, an important subject for future studies. The foraging conditions for Golden Plover chicks in Fennoscandia appear to be different to those in the UK, where the chicks rely mainly on a Tipulidae flush only.     

Coexistence of Lutjanus peru and Lutjanus guttatus (Pisces: Lutjanidae) in the coast of Guerrero, México: association with the temporal variation of recruitment

Monthly volumes of capture of Lutjanus peru and Lutjanus guttatus from the coast of Guerrero, Mexico, were analyzed considering eight annual cycles. Time-series, auto correlation, and cross-correlation analysis showed that monthly abundance of populations display unsystematic variations. The FiSAT software was used to obtain the recruitment patterns of both species, using length-frequency data. Our results support the hypothesis that temporal phase-shifts in reproductive events, hence recruitment, explain the coexistence of these species. The outcome of this mechanism is a temporal succession of specific recruit abundance off the coasts of Guerrero, Mexico. The uncoupling of the recruitment events between these species, induces a separation of recruits: therefore, the intake of a particular set of preys could take place at different times.     

Understanding the properties of aerobic sludge granules as hydrogels

Aerobic sludge granules are larger, denser microbial aggregates than activated sludge flocs with a smoother and more regular surface, which facilitates greater wastewater treatment intensity. Factors important in their growth are still poorly understood, which is an impediment to the construction and operation of full-scale aerobic sludge granule processes. Data in this article obtained with granules treating an abattoir wastewater provide evidence that aerobic sludge granules are hydrogels. The results also demonstrate a method for characterizing macromolecular associations. The rheological profile of these granules was found to be analogous with that of typical polymer gels. Water uptake or swelling reflects an equilibrium between granule elastic modulus and osmotic pressure, whereby uptake is increased by reducing solute concentration or the elastic modulus. A weakening of the extracellular polymeric substance (EPS) matrix as demonstrated with mechanical spectroscopy was induced by several environmental factors including temperature, pH and ionic strength. Uniform and elastic deformation was observed at low strain. Enzymatic degradation studies indicate that proteins and alpha-polysaccharides were the major granule structural materials. The aerobic sludge granules in the current study were therefore protein-polysaccharide composite physical hydrogels. While aerobic sludge granules treating an abattoir wastewater are used as a case study, many of the fundamental principles detailed here are relevant to other granulation processes. The paradigm established in this study can potentially be applied to better understand the formation of aerobic sludge granules and thus overcome a hurdle in the acceptance of aerobic sludge granulation as an alternative to more traditional wastewater treatment processes.     

Negative control of BAK1 by protein phosphatase 2A during plant innate immunity

Recognition of pathogen‐associated molecular patterns (PAMPs) by surface‐localized pattern‐recognition receptors (PRRs) activates plant innate immunity, mainly through activation of numerous protein kinases. Appropriate induction of immune responses must be tightly regulated, as many of the kinases involved have an intrinsic high activity and are also regulated by other external and endogenous stimuli. Previous evidences suggest that PAMP‐triggered immunity (PTI) is under constant negative regulation by protein phosphatases but the underlying molecular mechanisms remain unknown. Here, we show that protein Ser/Thr phosphatase type 2A (PP2A) controls the activation of PRR complexes by modulating the phosphostatus of the co‐receptor and positive regulator BAK1. A potential PP2A holoenzyme composed of the subunits A1, C4, and B’η/ζ inhibits immune responses triggered by several PAMPs and anti‐bacterial immunity. PP2A constitutively associates with BAK1 in planta. Impairment in this PP2A‐based regulation leads to increased steady‐state BAK1 phosphorylation, which can poise enhanced immune responses. This work identifies PP2A as an important negative regulator of plant innate immunity that controls BAK1 activation in surface‐localized immune receptor complexes.     

Effect of temperature and starvation upon survival strategies of Pseudomonas fluorescens CHA0: comparison with Escherichia coli

Microorganisms in aquatic systems are exposed to continuous modifications in their environmental conditions. In these systems, both autochthonous and allochthonous bacteria respond to adverse conditions by expressing viable but nonculturable phenotype. On the basis of this common response, the behaviour of a few species is extrapolated to others. We compared the survival strategies of Escherichia coli (allochthonous, mesophile bacterium) and Pseudomonas fluorescens CHA0 (ubiquitous, psychrotrophic bacteria) under nonoptimal temperature and nutrient deprivation. In the absence of nutrients, the effect of temperature on the loss of culturability did not show a common pattern. Whereas the survival of E. coli had an inverse relationship with temperature, whereas for P. fluorescens a direct relationship between temperature and T?? values was only established in the range 5-15°C, with an inverse relationship at higher temperatures. When the subproteome of the outer membrane of P. fluorescens was comparatively analysed, starvation was not the main source of change. The most relevant modifications were due to variations in temperature. OprF, the major surface protein of the genus Pseudomonas, showed a high expression in nonculturable as well as culturable populations under all the adverse situations analysed. We therefore propose OprF as a suitable marker for Pseudomonas detection in the environment.     

The contribution of induction of temperate phages to the numbers of free somatic coliphages in waters is not significant

Somatic coliphages have been proposed as indicators of water quality. But several factors have been considered a drawback for their use as indicators. We evaluated the contribution of temperate phages to the numbers of somatic coliphages detected in water by ISO (International Standards Organization) standardised methods. Prophage induction from naturally occurring bacteria was assayed with mitomycin C, ciprofloxacin and UV irradiation. Results indicate that the presence of prophages will not influence the determinations of somatic coliphages in water.