Assessment of Heat Resistance of Bacterial Spores from Food Product Isolates by Fluorescence Monitoring of Dipicolinic Acid Release

This study is aimed at the development and application of a convenient and rapid optical assay to monitor the wet-heat resistance of bacterial endospores occurring in food samples. We tested the feasibility of measuring the release of the abundant spore component dipicolinic acid (DPA) as a probe for heat inactivation. Spores were isolated from the laboratory type strain Bacillus subtilis 168 and from two food product isolates, Bacillus subtilis A163 and Bacillus sporothermodurans IC4. Spores from the lab strain appeared much less heat resistant than those from the two food product isolates. The decimal reduction times (D values) for spores from strains 168, A163, and IC4 recovered on Trypticase soy agar were 1.4, 0.7, and 0.3 min at 105°C, 120°C, and 131°C, respectively. The estimated Z values were 6.3°C, 6.1°C, and 9.7°C, respectively. The extent of DPA release from the three spore crops was monitored as a function of incubation time and temperature. DPA concentrations were determined by measuring the emission at 545 nm of the fluorescent terbium-DPA complex in a microtiter plate fluorometer. We defined spore heat resistance as the critical DPA release temperature (T_c), the temperature at which half the DPA content has been released within a fixed incubation time. We found T_c values for spores from Bacillus strains 168, A163, and IC4 of 108°C, 121°C, and 131°C, respectively. On the basis of these observations, we developed a quantitative model that describes the time and temperature dependence of the experimentally determined extent of DPA release and spore inactivation. The model predicts a DPA release rate profile for each inactivated spore. In addition, it uncovers remarkable differences in the values for the temperature dependence parameters for the rate of spore inactivation, DPA release duration, and DPA release delay.     

Block of Nav1.8 by small molecules

Sodium channels are key proteins in regulating neuronal excitability and accumulating data suggest that specific subtypes of voltage-dependent sodium channels are important in signaling various types of pain. Consistent with this theme, Jarvis et al.(7) recently reported the identification of a subtype-selective Na(v)1.8 blocker that was active in several pre-clinical models of pain. During the course of these studies compounds were also identified that showed large differences in potency when tested on Na(v)1.8 channels from different species. This addendum illustrates one of these compounds along with the potency correlation between recombinant and native tetrodotoxin-resistant sodium channels for additional examples. These data show that significant differences can be observed for sodium channel blockers across species and highlight the importance of considering this possibility when searching for new compounds and research tools to probe sodium channel function.     

An evolutionary perspective on caching by corvids

A principal finding in the food-caching literature is that species differences in hoarding propensity are positively correlated with species differences in degree of adaptations to caching behaviour, such as performance on spatial memory tasks and hippocampal volume. However, there are examples that do not fit this pattern. We argue that these examples can be better understood by considering the phylogenetic relatedness between species. We reconstruct the ancestral state for caching behaviour in corvids and assess when transitions in caching behaviour occurred within the corvid phylogeny. Our analysis shows that the common ancestor of all corvids was a moderate cacher. This result suggests that corvids followed a bi-directional evolutionary trajectory in which caching was secondarily lost twice and there were at least two independent transitions from moderate to specialized caching. The independent evolution of specialized cachers in the two groups must, therefore, be a case of convergent evolution. This is exemplified by the fact that specialized cachers show structurally different adaptations serving the same function to intense caching, such as different pouches to transport food. Finally, we argue that convergent evolution may have led to adaptations in memory and hippocampus that serve the same function but differ in design, and that these different adaptations may explain the examples that do not fit the pattern predicted by the adaptive specialization hypothesis.     

Initial events in the photocycle of photoactive yellow protein

The light-induced isomerization of a double bond is the key event that allows the conversion of light energy into a structural change in photoactive proteins for many light-mediated biological processes, such as vision, photosynthesis, photomorphogenesis, and photo movement. Cofactors such as retinals, linear tetrapyrroles, and 4-hydroxy-cinnamic acid have been selected by nature that provide the essential double bond to transduce the light signal into a conformational change and eventually, a physiological response. Here we report the first events after light excitation of the latter chromophore, containing a single ethylene double bond, in a low temperature crystallographic study of the photoactive yellow protein. We measured experimental phases to overcome possible model bias, corrected for minimized radiation damage, and measured absorption spectra of crystals to analyze the photoproducts formed. The data show a mechanism for the light activation of photoactive yellow protein, where the energy to drive the remainder of the conformational changes is stored in a slightly strained but fully cis-chromophore configuration. In addition, our data indicate a role for backbone rearrangements during the very early structural events.     

Vermunt AMW,Vermeesch AMG,de Kort CAD (1997): Purification and characterization of juvenile hormone esterase hemolymph of the Colorado potato beetle. Arch Insect Biochem Physiol 35:261–277.

The last sentence in the abstract was printed incorrectly. The correct sentence is printed below in the abstract. The authors regret the error. In the Colorado potato beetle (Leptinotarsa decemlineata), low juvenile hormone (JH) titers are necessary to initiate metamorphosis and diapause. Low JH titers coincide with high activities of JH esterase, which occur mainly in the hemolymph. The specific activity of JH esterase appeared to be highest in the last larval instar, at day 3 after the moult, and reached a value of 13.5 nmol/min/mg. JH esterase was purified from hemolymph collected at this stage by a sequence of separation systems including preparative nondenaturing PAGE, isoelectric focusing and SDS-PAGE. The enzyme was demonstrated to have a molecular weight of 120,000 and was composed of two subunits with molecular weight of 57,000, which were not linked by disulphide bridges. Isoelectric focusing revealed two forms of the enzyme with isoelectric points of 5.5 and 5.6. The K_m and k_cat of the purified enzyme were determined. The major form with pI 5.6 had a K_m of 1.4 × 10^–6M and a k_cat of 0.9 s^–1 and the minor form with pI 5.5 had a K_m of 2.2 × 10^–6M and a k_cat 1.9 s^–1. The quaternary structure of L. Decemlineata JH esterase as a dimer, differs from JH esterases in other species, which are monomers.     

Structure of Colorado potato beetle lipophorin: differential scanning calorimetric and small-angle X-ray scattering studies

The structure of lipophorin, isolated from hemolymph of the Colorado potato beetle, was investigated by differential scanning calorimetry (DSC) and small-angle X-ray scattering. The DSC heating curves of intact lipophorin showed endothermic peaks that were similar to peaks obtained with the hydrocarbon fraction isolated from this lipophorin. The observed peaks correlated with the transition of the hydrocarbons from an ordered into a more disordered state. Changes in structure of the lipophorin particles with increasing temperature were also observed by small-angle X-ray scattering studies. The structural organization of lipophorin was further elucidated by simulation analysis, using a three-layered symmetrical sphere as a model. These studies revealed that lipophorin from the Colorado potato beetle is a sphere with a maximum diameter of 175 A. The sphere is composed of three radially symmetrical layers of different electron densities. The outer layer (37.5-39.5 A in thickness) is composed of phospholipid, apolipophorin I, and part of apolipophorin II. The middle layer (5-10 A) contains diacylglycerol, the rest of apolipophorin II, and probably beta-carotene. The core of the particle (40-45 A) only contains hydrocarbons. This structure differs from another model, previously proposed for cockroach and locust lipophorins [Katagiri, C., Sato, M., & Tanaka N. (1987) J. Biol. Chem. 262, 15857-15861], in the small size of the middle layer. The volume of the middle layer correlated well with the low diacylglycerol content of this lipophorin.     

Above‐ and belowground linkages in Sphagnum peatland: climate warming affects plant‐microbial interactions

Peatlands contain approximately one third of all soil organic carbon (SOC). Warming can alter above‐ and belowground linkages that regulate soil organic carbon dynamics and C‐balance in peatlands. Here we examine the multiyear impact of in situ experimental warming on the microbial food web, vegetation, and their feedbacks with soil chemistry. We provide evidence of both positive and negative impacts of warming on specific microbial functional groups, leading to destabilization of the microbial food web. We observed a strong reduction (70%) in the biomass of top‐predators (testate amoebae) in warmed plots. Such a loss caused a shortening of microbial food chains, which in turn stimulated microbial activity, leading to slight increases in levels of nutrients and labile C in water. We further show that warming altered the regulatory role of Sphagnum‐polyphenols on microbial community structure with a potential inhibition of top predators. In addition, warming caused a decrease in Sphagnum cover and an increase in vascular plant cover. Using structural equation modelling, we show that changes in the microbial food web affected the relationships between plants, soil water chemistry, and microbial communities. These results suggest that warming will destabilize C and nutrient recycling of peatlands via changes in above‐ and belowground linkages, and therefore, the microbial food web associated with mosses will feedback positively to global warming by destabilizing the carbon cycle. This study confirms that microbial food webs thus constitute a key element in the functioning of peatland ecosystems. Their study can help understand how mosses, as ecosystem engineers, tightly regulate biogeochemical cycling and climate feedback in peatlands     

Palaeoenvironment and taphonomy of a Late Jurassic (Late Tithonian) Lagerstätte from central Poland

A rich assemblage of exceptionally preserved marine and terrestrial fossils occurs in fine‐grained limestones in the upper part of the Late Tithonian (Middle Volgian) shallowing upward carbonate sequence in Central Poland. The richest horizon, a deposit known locally as the Corbulomima horizon, is named after the shallow burrowing suspension feeding bivalve Corbulomima obscura, moulds of which occur in densities of up to 500 per square metre on some bedding planes. The fauna in this bed also includes organic and phosphatic remains of a wide range of other creatures including the exuviae of limulids and decapods, disarticulated fish skeletons and rare isolated pterosaur bones and teeth. There are also perfectly preserved dragonfly wings and beetle exoskeletons. The average stable carbon and oxygen isotope values for ostracod shells and fine‐grained sediment from this horizon suggest precipitation of the calcium carbonate from warm seawater of normal marine salinity. The carbonate sediments overlying the fossiliferous horizon have been interpreted as nearshore to shoreface facies. These pass abruptly into coarse reworked intraclastic sediments interpreted as possible tsunami or storm surge over‐wash deposits. The clasts in this deposit have more positive oxygen isotope values than those in the underlying limestone, which may indicate that they were lithified in a slightly more evaporative, perhaps intertidal, setting. The succession terminates with silicified fine‐grained limestones likely to have formed in extremely shallow lagoonal environments. In contrast with the Solnhofen limestones of Lower Tithonian age in south‐central Germany the Corbulomima horizon is interpreted as a transitional deposit formed in a shallow marine setting by rapid burial with elements of both Konservat‐ and Konzentrat‐Lagerstätte preservation. □Konzentrat and Konservat‐Lagerstätte, Taphonomy, Palaeoenvironment, Paleogeography, Late Jurassic, Poland.