Patterns of interaction specificity of fungus-growing termites and <Emphasis Type="Italic">Termitomyces</Emphasis> symbionts in South Africa

Background  

Termites of the subfamily Macrotermitinae live in a mutualistic symbiosis with basidiomycete fungi of the genus Termitomyces. Here, we explored interaction specificity in fungus-growing termites using samples from 101 colonies in South-Africa and Senegal, belonging to eight species divided over three genera. Knowledge of interaction specificity is important to test the hypothesis that inhabitants (symbionts) are taxonomically less diverse than 'exhabitants' (hosts) and to test the hypothesis that transmission mode is an important determinant for interaction specificity.     

Long-range interactions of <Emphasis Type="Italic">Chara</Emphasis> chloroplasts are sensitive to plasma-membrane H<Superscript>+</Superscript> flows and comprise separate photo- and dark-operated pathways

Local illumination of the characean internode with a 30-s pulse of white light was found to induce the delayed transient increase of modulated chlorophyll fluorescence in shaded cell parts, provided the analyzed region is located downstream in the cytoplasmic flow at millimeter distances from the light spot. The fluorescence response to photostimulation of a remote cell region indicates that the metabolites produced by source chloroplasts in an illuminated region are carried downstream with the cytoplasmic flow, thus ensuring long-distance communications between anchored plastids in giant internodal cells. The properties of individual stages of metabolite signaling are not yet well known. We show here that the export of assimilates and/or reducing equivalents from the source chloroplasts into the flowing cytoplasm is largely insensitive to the direction of plasma-membrane H⁺ flows, whereas the events in sink regions where these metabolites are delivered to the acceptor chloroplasts under dim light are controlled by H⁺ fluxes across the plasma membrane. The fluorescence response to local illumination of remote cell regions was best pronounced under weak background light and was also observed in a modified form within 1–2 min after the transfer of cell to darkness. The fluorescence transients in darkened cells were suppressed by antimycin A, an inhibitor of electron transfer from ferredoxin to plastoquinone, whereas the fluorescence response under background light was insensitive to this inhibitor. We conclude that the accumulation of reduced metabolites in the stroma leads to the reduction of photosystem II primary quinone acceptor (Q_A) via two separate (photochemical and non-photochemical) pathways.     

Relative importance of colonist quantity,quality, and arrival frequency to the extinction of two zooplankton species

Introduced plants can positively affect population viability by augmenting the diet of native herbivores, but can negatively affect populations if they are subpar or toxic resources. In organisms with complex life histories, such as insects specializing on host plants, the impacts of a novel host may differ across life stages, with divergent effects on population persistence. Most research on effects of novel hosts has focused on adult oviposition preference and larval performance, but adult preference may not optimize offspring performance, nor be indicative of host quality from a demographic perspective. We compared population growth rates of the Baltimore checkerspot butterfly, Euphydryas phaeton, on an introduced host, Plantago lanceolata (English plantain), and the native host Chelone glabra (white turtlehead). Contrary to the previous findings suggesting that P. lanceolata could be a population sink, we found higher population growth rates (λ) on the introduced than the native host, even though some component parameters of λ were higher on the native host. Our findings illustrate the importance of moving beyond preference–performance studies to integrate vital rates across all life stages for evaluating herbivore–host plant relationships. Single measures of preference or performance are not sufficient proxies for overall host quality nor do they provide insights into longer term consequences of novel host plant use. In our system, in particular, P. lanceolata may buffer checkerspot populations when the native host is limiting, but high growth rates could lead to crashes over longer time scales.     

Current advances in molecular methods for detection of nitrite-dependent anaerobic methane oxidizing bacteria in natural environments

Nitrite-dependent anaerobic methane oxidation (n-damo) process uniquely links microbial nitrogen and carbon cycles. Research on n-damo bacteria progresses quickly with experimental evidences through enrichment cultures. Polymerase chain reaction (PCR)-based methods for detecting them in various natural ecosystems and engineered systems play a very important role in the discovery of their distribution, abundance, and biodiversity in the ecosystems. Important characteristics of n-damo enrichments were obtained and their key significance in microbial nitrogen and carbon cycles was investigated. The molecular methods currently used in detecting n-damo bacteria were comprehensively reviewed and discussed for their strengths and limitations in applications with a wide range of samples. The pmoA gene-based PCR primers for n-damo bacterial detection were evaluated and, in particular, several incorrectly stated PCR primer nucleotide sequences in the published papers were also pointed out to allow correct applications of the PCR primers in current and future investigations. Furthermore, this review also offers the future perspectives of n-damo bacteria based on current information and methods available for a better acquisition of new knowledge about this group of bacteria.     

Structural and functional consequences of single amino acid substitutions in the pyrimidine base binding pocket of Escherichia coli CMP kinase

Bacterial CMP kinases are specific for CMP and dCMP, whereas the related eukaryotic NMP kinase phosphorylates CMP and UMP with similar efficiency. To explain these differences in structural terms, we investigated the contribution of four key amino acids interacting with the pyrimidine ring of CMP (Ser36, Asp132, Arg110 and Arg188) to the stability, catalysis and substrate specificity of Escherichia coli CMP kinase. In contrast to eukaryotic UMP/CMP kinases, which interact with the nucleobase via one or two water molecules, bacterial CMP kinase has a narrower NMP-binding pocket and a hydrogen-bonding network involving the pyrimidine moiety specific for the cytosine nucleobase. The side chains of Arg110 and Ser36 cannot establish hydrogen bonds with UMP, and their substitution by hydrophobic amino acids simultaneously affects the K(m) of CMP/dCMP and the k(cat) value. Substitution of Ser for Asp132 results in a moderate decrease in stability without significant changes in K(m) value for CMP and dCMP. Replacement of Arg188 with Met does not affect enzyme stability but dramatically decreases the k(cat)/K(m) ratio compared with wild-type enzyme. This effect might be explained by opening of the enzyme/nucleotide complex, so that the sugar no longer interacts with Asp185. The reaction rate for different modified CMP kinases with ATP as a variable substrate indicated that none of changes induced by these amino acid substitutions was 'propagated' to the ATP subsite. This 'modular' behavior of E. coli CMP kinase is unique in comparison with other NMP kinases.     

Hemlock woolly adelgid invasion affects microhabitat characteristics and small mammal communities

Hemlock woolly adelgid (HWA) invasion and preemptive logging practices alter the habitat structure of New England forests and may indirectly affect associated small mammal communities. Microhabitat structure was measured and small mammals were censused in eight large experimental plots to quantify these effects. The Harvard Forest long-term ecological research experiment is a replicated two-block design that includes four ~ 0.81-ha canopy treatments: (1) hemlock control, (2) hardwood control, (3) girdled Treatment, in which hemlock trees were killed by girdling in 2005 and left standing to simulate HWA invasion, and (4) logged treatment, in which trees were removed to simulate preemptive logging management practices. Nine microhabitat characteristics were measured from plot photos revealing differences among ground and canopy microhabitat structure. Small mammals were censused during high (2012) and low (2013) abundant years. Populations of common species were estimated with mark-recapture analysis. Peromyscus spp. were not affected by treatment in either year, but southern red-backed vole populations were greatest in the girdled treatments in 2012 and rarely captured in 2013. Between 6 and 9 mammal species were recorded in all treatments and species composition varied slightly. Estimated species richness was greater in girdled treatments than hemlock controls, but did not differ between girdled and logged treatments, which suggests preemptive logging is as detrimental to some small mammal species as HWA invasion. Overall, there is little evidence of a major shift in small mammal community structure in response to HWA invasion, with only minor changes in relative abundance both years.     

Chromosome substitutions and recombination in the amphiploid Lolium perenne×Festuca pratensis cv Prior (2n=4x=28)

 The synthetic amphiploid cv Prior was created in the early 1970s at the Welsh Plant Breeding Station by crossing colchicine-induced autotetraploids of Lolium perenne (2n=14) and Festuca pratensis (2n=14). Meiosis in the early generations was characterized as stable, with frequent bivalent formation. In situ hybridization of a L. perenne total genomic DNA probe to mitotic chromosome spreads of 12 plants, from two extant populations of Prior, demonstrates extensive recombination between the two genomes. Recombination events occur along the whole length of chromosome arms but with a higher frequency in the medial portion. The species origins of chromosomes were assigned by the presence or absence of a fluorescent probe at the centromere. There has been a substitution of Festuca-origin chromosomes by those of Lolium-origin, resulting in a mean of 17.9 (15–21) Lolium and 9.7 (7–13) Festuca chromosomes per genotype. Mean chromatin length per genotype comprised 62.1% Lolium and 37.9% Festuca. On average 9.3 Lolium (51.1% of those present) and 3.5 Festuca (37.8%) chromosomes had no recombined segments. For chromosomes which did show recombination, fewer alien segments were observed in Lolium than in Festuca chromosomes. Festuca chromosomes in genotypes selected for drought resistance had undergone more recombination than in genotypes from an unselected population, though this difference was not statistically significant for the small sample examined. Received: 16 June 1998 / Accepted: 17 September 1998 RID="1" ID="1" <E5>Present address:</E5> Lithuanian Institute of Agriculture, 5051 Dotnuva-Akademija, Kedainiai, Lithuania RID=" ID=" Communicated by J. W. Snape RID=" ID=" <E5>Correspondence to</E5> P. H. Canter     

Investigation of the ‘double cross’ splitting mechanism of single-crystal diamond under nanoindentation via molecular dynamics simulation

Elucidating the mechanical response of diamond is a difficult task due to its ultrahard nature. Here, we applied a molecular dynamics (MD) method to investigate the mechanical response of single-crystal diamond under nanoindentation. There was no obvious “pop in” phenomenon on the load–depth curve, and the elastic modulus deduced from the curve was 1128 GPa, which was similar to the value obtained from experimental measurements. Results from computed tomography (CT) and the coordination number showed that the distribution of the mismatched C atoms around the deformation zone took the form of a ‘double cross.’ The atoms around the indenter tip could be divided into two zones, a translation zone and a lattice distortion zone, based on their movements. Subsequent first-principles calculations revealed that the C-atom displacement barrier varied significantly with direction, which resulted in shear stress between the two zones and the formation of the double-cross splitting.

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Graphical Abstract The displacement of the atoms around the indenter tip