Strong Synergy between a Eukaryotic Antimicrobial Peptide and Bacteriocins from Lactic Acid Bacteria

The antimicrobial effect obtained upon combining the prokaryotic antimicrobial peptides (AMPs; more commonly referred to as bacteriocins) pediocin PA-1, sakacin P, and curvacin A (all produced by lactic acid bacteria [LAB]) with the eukaryotic AMP pleurocidin (from fish) has been investigated. The three LAB AMPs alone were active against gram-positive Listeria ivanovii bacteria at nanomolar concentrations, whereas they were inactive against gram-negative Escherichia coli bacteria. Pleurocidin alone was active against both of these types of bacteria at micromolar concentrations. Little if any synergy between the LAB AMPs and pleurocidin against the gram-positive L. ivanovii strain was obtained. In contrast, the LAB AMPs and pleurocidin acted highly synergistically against the gram-negative E. coli strain. Nanomolar concentrations of LAB AMPs increased the growth inhibitory potency of pleurocidin by about fourfold. When micromolar concentrations of LAB AMPs were combined with 2 μg of pleurocidin/ml, 100% growth inhibition was attained, whereas pleurocidin alone at a concentration of 2 μg/ml gave no growth inhibition. Most noteworthy, when high concentrations (128 μg/ml) of pleurocidin in the absence of LAB AMPs were used over a long period of incubation (1 week), some growth of E. coli was observed, whereas 16 μg of pleurocidin/ml completely abolished growth in the presence of 64 to 128 ng of LAB AMPs/ml over the same period of time. The results clearly demonstrate that combining eukaryotic and prokaryotic AMPs can greatly increase the specific activity and broaden the target-cell range of these peptides.     

Chaunopycnis pustulata sp. nov., a new clavicipitalean anamorph producing metabolites that modulate potassium ion channels

Two morphologically similar strains of hyphomycetous fungi, MF5785 and MF5638, produced potent indole diterpene antagonists of the calcium-gated potassium ion channel, Maxi-K, and a diterpene blocker (nalanthalide) of the voltage-gated potassium channel, Kv 1.3, respectively. The two strains were tentatively identified in the literature as Nalanthamala species. Analyses of their secondary metabolite profiles by HPLC and mass spectroscopy demonstrated that both produced a series of indole diterpenes, of which at least one was produced by both strains. Another strain, Chaunopycnis alba (MF6799), that produced the diterpene, nalanthalide, also produced indole diterpene metabolites. Morphological comparisons and phylogenetic studies based on 28S and ITS rDNA sequences indicated that MF5785 and MF5368, and another soil-derived strain GB6597, belonged to a monophyletic clade of the Clavicipitaceae that included the anamorph Chaunopycnis alba and several Cordyceps and Tolypocladium species. A new species of Chaunopycnis is therefore proposed to accommodate MF5785, MF5368, and GB6597. The possible synonymy of Albophoma yamanashiensis with C. alba also is discussed. Within the Clavicipitaceae, indole diterpenoid compounds have only been known from the graminicolous species (subfamily Clavicipitoideae); therefore delineation of a Chaunopycnis clade has revealed a previously unrecognized lineage of indole diterpene-producing fungi among the subfamily Cordycipitoideae.     

Role of skin blood flow and sweating rate in exercise thermoregulation after bed rest.

Two potential mechanisms, reduced skin blood flow (SBF) and sweating rate (SR), may be responsible for elevated intestinal temperature (T(in)) during exercise after bed rest and spaceflight. Seven men underwent 13 days of 6 degrees head-down bed rest. Pre- and post-bed rest, subjects completed supine submaximal cycle ergometry (20 min at 40% and 20 min at 65% of pre-bed rest supine peak exercise capacity) in a thermoneutral room. After bed rest, T(in) was elevated at rest (+0.31 +/- 0.12 degrees C) and at the end of exercise (+0.33 +/- 0.07 degrees C). Percent increase in SBF during exercise was less after bed rest (211 +/- 53 vs. 96 +/- 31%; P < or = 0.05), SBF/T(in) threshold was greater (37.09 +/- 0.16 vs. 37.33 +/- 0.13 degrees C; P < or = 0.05), and slope of SBF/T(in) tended to be reduced (536 +/- 184 vs. 201 +/- 46%/ degrees C; P = 0.08). SR/T(in) threshold was delayed (37.06 +/- 0.11 vs. 37.34 +/- 0.06 degrees C; P < or = 0.05), but the slope of SR/T(in) (3.45 +/- 1.22 vs. 2.58 +/- 0.71 mg x min-1 x cm-2 x degrees C-1) and total sweat loss (0.42 +/- 0.06 vs. 0.44 +/- 0.08 kg) were not changed. The higher resting and exercise T(in) and delayed onset of SBF and SR suggest a centrally mediated elevation in the thermoregulatory set point during bed rest exposure.     

Computer-aided studies of vision in crabs

A system for the back projection of computer-generated visual images onto a screen or screens that cover 240° of the horizontal visual field is described. Its applicability for the study of crab vision is tested by comparing the frequency response of the optokinetic response of the land crab, Cardisoma guanhumi , to sinusoidal oscillation of computer-generated striped patterns and a real striped drum. Significant differences were observed only at the low end of the frequency spectrum. The flexibility of computer-generated visual stimulation and its advantages for the study of optic flow are illustrated by experiments that: (a) demonstrate how well crabs separate the translational and rotational components of optic flow by showing compensatory eye movements to only the latter; (b) show that the ability to compensate for rotation is not impaired by combinations of rotation and translation; (c) show that motion parallax cues are used in addition to previously-described global cues for making the distinction between rotation and translation. Finally, the use of these methods in a successful search for visual interneurones sensitive to optic flow stimuli is demonstrated for the shore crab, Carcinus maenas .     

Extent of invasion of Tasmanian native vegetation by the exotic bumblebee Bombus terrestris (Apoidea: Apidae)

Abstract Observations of the large earth bumblebee, Bombus terrestris (L.), in native vegetation were collated to determine the extent to which this exotic species has invaded Tasmanian native vegetation during the first 9 years after its introduction. The range of B. terrestris now encompasses all of Tasmania's major vegetation types, altitudes from sea level to 1260m a.s.L, and the entire breadth of annual precipitation in the state from more than 3200 mm to less than 600 mm. Observations of workers carrying pollen, together with the presence of large numbers of bumblebees at many localities across this range indicate that colonies are frequently established in native vegetation. Evidence that colonies are often successful was obtained from repeated observations of the species during more than 1 year at particular sites. Unequivocal evidence of colonies was obtained from six National Parks, including four of the five in the Tasmanian Wilderness World Heritage Area (WHA). Indeed, the species has been present in the WHA for at least as long as it has in the city of Hobart, where it was first recorded. In southwestern Tasmania, evidence of colonies was obtained up to 40km from gardens, 61 km from small towns and 93 km from large towns. Hence, contrary to previous suggestions, the species is established in the most remote parts of Tasmania and is not dependent on introduced garden plants. Given their strong record of invasion, it is likely that B. terrestris will form feral populations on the mainland of Australia and in many other parts of the world if introduced. Because of their likely negative impacts on native animals and plants, and potential to enhance seed production in weeds, the spread of bumblebees should be avoided.     

Spatio-temporal variation in Markov chain models of subtidal community succession

In this paper we ask whether succession in a rocky subtidal community varies in space and time, and if so how much affect that variation has on predictions of community dynamics and structure. We describe succession by Markov chain models based on observed frequencies of species replacements. We use loglinear analysis to detect and quantify spatio‐temporal variation in the transition matrices describing succession. The analysis shows that space and time, but not their interaction, have highly significant effects on transition probabilities. To explore the ecological importance of the spatio‐temporal variability detected in this analysis, we compare the equilibria and the transient dynamics among three Markov chain models: a time‐averaged model that includes the effects of space on succession, a spatially averaged model that include the effects of time, and a constant matrix that averages over the effects of space and time. All three models predicted similar equilibrium composition and similar rates of convergence to equilibrium, as measured by the damping ratio or the subdominant Lyapunov exponent. The predicted equilibria from all three models were very similar to the observed community structure. Thus, although spatial and temporal variation is statistically significant, at least in this system this variation does not prevent homogeneous models from predicting community structure.     

Microstructure of the neocortex: Comparative aspects

The appearance of the neocortex, its expansion, and its differentiation in mammals, represents one of the principal episodes in the evolution of the vertebrate brain. One of the fundamental questions in neuroscience is what is special about the neocortex of humans and how does it differ from that of other species? It is clear that distinct cortical areas show important differences within both the same and different species, and this has led to some researchers emphasizing the similarities whereas others focus on the differences. In general, despite of the large number of different elements that contribute to neocortical circuits, it is thought that neocortical neurons are organized into multiple, small repeating microcircuits, based around pyramidal cells and their input-output connections. These inputs originate from extrinsic afferent systems, excitatory glutamatergic spiny cells (which include other pyramidal cells and spiny stellate cells), and inhibitory GABAergic interneurons. The problem is that the neuronal elements that make up the basic microcircuit are differentiated into subtypes, some of which are lacking or highly modified in different cortical areas or species. Furthermore, the number of neurons contained in a discrete vertical cylinder of cortical tissue varies across species. Additionally, it has been shown that the neuropil in different cortical areas of the human, rat and mouse has a characteristic layer specific synaptology. These variations most likely reflect functional differences in the specific cortical circuits. The laminar specific similarities between cortical areas and between species, with respect to the percentage, length and density of excitatory and inhibitory synapses, and to the number of synapses per neuron, might be considered as the basic cortical building bricks. In turn, the differences probably indicate the evolutionary adaptation of excitatory and inhibitory circuits to particular functions.