16 Mechanical energy,protein motion,and the possible origin of life between mica sheets

The origins of life require reliable energy sources. One feasible energy source has not been considered until recently. This is mechanical energy-work (Hansma, 2010, 2012). The spaces between moving muscovite mica sheets are the environment in which mechanical energy is hypothesized to have been involved in the origins of life. Mechanical energy from moving mica sheets has two main sources: (1) The open-and-shut motions of mica sheets in response to water movements in and out between the sheets, and (2) Thermal cycles of day and night acting on bubble ‘defects’ between mica sheets. This mechanical energy is hypothesized to have been involved in the formation (and breaking) of covalent bonds, the rearrangement of polymers and molecular aggregates, and the budding-off of protocells, in the earliest form of cell division. Furthermore, it is hypothesized that the mechanical energy from mica sheets moving open-and-shut is the source of the common open-and-shut motions of enzymes, originating from a protobiotic era when mechanical energy was plentiful and chemical energy was not yet available.     

A preliminary assessment of congruence between biodiversity patterns in Afrotropical forest birds and forest mammals

Burgess, N., de Klerk, H., Fjeldsá, J., Crowe, T. & Rahbek, R. 2000. A preliminary assessment of congruence between biodiversity patterns in Afrotropical forest birds and forest mammals. Ostrich 71 (1 & 2): 286–291.

Databases compiled for forest birds and forest mammals in the Afrotropics were tested for congruence of overall patterns and hotspots of species richness and endemism. We also looked at how well a near-minimum set of priority areas for one taxon catered for the second taxon. Overall species richness and richness hotspots of forest birds were significantly correlated with those of forest mammals, as was the case for overall endemism. Endemism hotspots for forest birds and mammals were not significantly correlated. The near-minimum set for forest birds represented 136 (76.5%) forest mammal species. The near-minimum set for forest mammals represented 350 (93.62%) forest bird species. However, to represent all forest mammals three times each, 51 grids were needed in addition to the 78 chosen as a near-minimum set for forest birds, and to represent all forest birds three times each, 43 more grids were needed in addition to the 80 selected for forest mammals. There is some congruence between the patterns of richness, endemism and near-minimum sets for forest birds and mammals in the Afrotropics, but the one taxon does not provide the ideal conservation solution for the other. Further refinement of the databases used in this paper would allow for more rigorous testing of congruence between these two groups.     

Co-occurring grass species differ in their associated microbial community composition in a temperate native grassland

Background and aims

Specific associations exist between plant species and the soil microbial community and these associations vary between habitat types and different plant groups. However, there is evidence that the associations are highly specific. Hence, we aimed to determine the specificity of plant-microbe relationships amongst co-occurring grass species in a temperate grassland.

Methods and results

We examined the broad microbial groups of bacteria and fungi as well as a specific fungal group, the arbuscular mycorrhizal community amongst two dominant C₃ and C₄ species and one sub-dominant C₃ species using terminal restriction fragment length polymorphism (T-RFLP) analysis. We found that the two dominant species were more similar to each other in their bacterial and arbuscular mycorrhizal community composition than either was to the sub-dominant species, but not in their fungal community composition. We also found no clear evidence that those differences were directly linked to soil chemical properties.

Conclusions

Our results demonstrate that co-occurring grass species have a distinct soil microbial community and T-RFLP analysis is able to detect plant species effect on the microbial community composition on an extremely local scale, providing an insight into the differences in the response of bacterial, fungal and arbuscular mycorrhizal communities to different, but similar and co-occurring, plant species.     

A Pivotal Role for Tryptophan 447 in Enzymatic Coupling of Human Endothelial Nitric Oxide Synthase (eNOS): EFFECTS ON TETRAHYDROBIOPTERIN-DEPENDENT CATALYSIS AND eNOS DIMERIZATION*

Tetrahydrobiopterin (BH4) is a required cofactor for the synthesis of NO by NOS. Bioavailability of BH4 is a critical factor in regulating the balance between NO and superoxide production by endothelial NOS (eNOS coupling). Crystal structures of the mouse inducible NOS oxygenase domain reveal a homologous BH4-binding site located in the dimer interface and a conserved tryptophan residue that engages in hydrogen bonding or aromatic stacking interactions with the BH4 ring. The role of this residue in eNOS coupling remains unexplored. We overexpressed human eNOS W447A and W447F mutants in novel cell lines with tetracycline-regulated expression of human GTP cyclohydrolase I, the rate-limiting enzyme in BH4 synthesis, to determine the importance of BH4 and Trp-447 in eNOS uncoupling. NO production was abolished in eNOS-W447A cells and diminished in cells expressing W447F, despite high BH4 levels. eNOS-derived superoxide production was significantly elevated in W447A and W447F versus wild-type eNOS, and this was sufficient to oxidize BH4 to 7,8-dihydrobiopterin. In uncoupled, BH4-deficient cells, the deleterious effects of W447A mutation were greatly exacerbated, resulting in further attenuation of NO and greatly increased superoxide production. eNOS dimerization was attenuated in W447A eNOS cells and further reduced in BH4-deficient cells, as demonstrated using a novel split Renilla luciferase biosensor. Reduction of cellular BH4 levels resulted in a switch from an eNOS dimer to an eNOS monomer. These data reveal a key role for Trp-447 in determining NO versus superoxide production by eNOS, by effects on BH4-dependent catalysis, and by modulating eNOS dimer formation.     

Legal Traditions,Environmental Awareness,and a Modern Industry: Comparative Legal Analysis and Marine Aquaculture

In the interests of increasing fish production globally, alleviating global poverty, and income generation, marine aquaculture has seen worldwide expansion over the past few decades. However, this expansion has been matched by growing concerns over its environmental impacts. This article utilizes comparative legal analysis to explore the legal systems of governance for the environmental performance of marine aquaculture in four case study countries. Two are members of the European Community (Scotland, as part of the United Kingdom, and Greece), one is a recent accession country (Slovenia), and the fourth is closely linked to the European Community albeit geographically and legally disparate (Israel).     

Multilocus Genotype Analysis of Escherichia coli O157 Isolates from Australia and the United States Provides Evidence of Geographic Divergence

Escherichia coli O157 is a food-borne pathogen whose major reservoir has been identified as cattle. Recent genetic information has indicated that populations of E. coli O157 from cattle and humans can differ genetically and that this variation may have an impact on their ability to cause severe human disease. In addition, there is emerging evidence that E. coli O157 strains from different geographical regions may also be genetically divergent. To investigate the extent of this variation, we used Shiga toxin bacteriophage insertion sites (SBI), lineage-specific polymorphisms (LSPA-6), multilocus variable-number tandem-repeat analysis (MLVA), and a tir 255T>A polymorphism to examine 606 isolates representing both Australian and U.S. cattle and human populations. Both uni- and multivariate analyses of these data show a strong association between the country of origin and multilocus genotypes (P < 0.0001). In addition, our results identify factors that may play a role in virulence that also differed in isolates from each country, including the carriage of stx₁ in the argW locus uniquely observed in Australian isolates and the much higher frequency of stx₂-positive (also referred to as stx_2a) strains in the U.S. isolates (4% of Australian isolates versus 72% of U.S. isolates). LSPA-6 lineages differed between the two continents, with the majority of Australian isolates belonging to lineage I/II (LI/II) (LI, 2%; LI/II, 85%; LII, 13%) and the majority of U.S. isolates belonging to LI (LI, 60%; LI/II, 16%; LII, 25%). The results of this study provide strong evidence of phylogeographic structuring of E. coli O157 populations, suggesting divergent evolution of enterohemorrhagic E. coli O157 in Australia and the United States.     

Aquaporin-4 water channels and synaptic plasticity in the hippocampus

Aquaporin-4 (AQP4) is the major water channel expressed in the central nervous system (CNS) and is primarily expressed in glial cells. Many studies have shown that AQP4 regulates the response of the CNS to insults or injury, but far less is known about the potential for AQP4 to influence synaptic plasticity or behavior. Recent studies have examined long-term potentiation (LTP), long-term depression (LTD), and behavior in AQP4 knockout (KO) and wild-type mice to gain more insight into its potential role. The results showed a selective effect of AQP4 deletion on LTP of the Schaffer collateral pathway in hippocampus using an LTP induction protocol that simulates pyramidal cell firing during theta oscillations (theta-burst stimulation; TBS). However, LTP produced by a different induction protocol was unaffected. There was also a defect in LTD after low frequency stimulation (LFS) in AQP4 KO mice. Interestingly, some slices from AQP4 KO mice exhibited LTD after TBS instead of LTP, or LTP following LFS instead of LTD. These data suggest that AQP4 and astrocytes influence the polarity of long-term synaptic plasticity (potentiation or depression). These potentially powerful roles expand the influence of AQP4 and astrocytes beyond the original suggestions related to regulation of extracellular potassium and water balance. Remarkably, AQP4 KO mice did not show deficits in basal transmission, suggesting specificity for long-term synaptic plasticity. The mechanism appears to be related to neurotrophins and specifically brain-derived neurotrophic factor (BDNF) because pharmacological blockade of neurotrophin trk receptors or scavenging ligands such as BDNF restored plasticity. The in vitro studies predicted effects in vivo of AQP4 deletion because AQP4 KO mice performed worse using a task that requires memory for the location of objects (object placement). However, performance on other hippocampal-dependent tasks was spared. The results suggest an unanticipated and selective role of AQP4 in synaptic plasticity and spatial memory, and underscore the growing appreciation of the role of glial cells in functions typically attributed to neurons. Implications for epilepsy are discussed because of the previous evidence that AQP4 influences seizures, and the role of synaptic plasticity in epileptogenesis.