Effects of Protoceratium reticulatum yessotoxin on feeding rates of Acartia hudsonica: A bioassay using artificial particles coated with purified toxin

Paralytic shellfish toxins produced by dinoflagellates are known to deter copepod grazing. Dinoflagellate species, including Protoceratium reticulatum, also produce disulfated polyether yessotoxins that were previously referred to as diarrheic shellfish toxins. However, the role of yessotoxins in predator–prey relationships is not yet clear. In the present study, the effects of purified yessotoxin (YTX) on feeding activities of Acartia hudsonica (Copepoda, Calanoida) were experimentally investigated. Polystyrene fluorescent microspheres (10 μm in diameter) colored bright blue or yellow-green were coated with cell extracts of P. reticulatum that do not produce yessotoxins. The bright blue microspheres were further coated with YTX, and the yellow-green microspheres were used as the reference. The microspheres were then given to the copepods separately or in combination to measure clearance rates and feeding selectivity. A. hudsonica was found to feed on the yellow-green microspheres without YTX at twice the rate of the bright blue microspheres with YTX. We also confirmed that microsphere color per se did not affect the feeding rates. The bright blue microspheres adsorbed 1.8–43.3 pg of YTX per microsphere, which is similar to the cell-specific yessotoxin content of toxic P. reticulatum found in natural environments. These results suggest that production of yessotoxin is advantageous for P. reticulatum by deterring predation by copepods.     

Differential sensitivity of fungi to lithium chloride in culture media

Forty species of fungi, representing a range of ecological and taxonomic groups, were tested for their ability to grow on agar media amended with lithium chloride (LiCl) at 1.5, 3 and 6 g l⁻¹. Species of Trichoderma varied considerably in their sensitivity to LiCl; at one week on 6 g l⁻¹ LiCl medium, the growth of seven species of Trichoderma was considerably inhibited; however, by three weeks at this level, four of the species tested were able to attain ≥30 % of control growth. Of the seven species tested, an isolate of T. viride was the most sensitive to LiCl in agar. Eleven other imperfect fungi also showed a range of ability to grow on agar amended with LiCl, from total inhibition to complete lack of inhibition. Six ascomycete fungi were greatly inhibited by LiCl at all levels; however, an isolate of Chaetomium globosum was highly tolerant of LiCl. Seven basidiomycete wood-decay fungi were quite sensitive to LiCl in agar, showing total to nearly total inhibition even at the lowest level; however, after three weeks, an isolate of Postia placenta was nearly uninhibited except at 6 g l⁻¹. Five ectomycorrhizal basidiomycete fungi were totally inhibited by all levels of LiCl; however, one ectomycorrhizal imperfect fungus (Cenococcum graniforme) was able to grow at 3 g l⁻¹ and was uninhibited at 1.5 g l⁻¹. Four zygomycete fungus isolates were nearly unaffected in their growth by all levels of LiCl.     

A quantitative analysis of behavioral selectivity for pulse rise-time in the gray treefrog, Hyla versicolor

The selectivity of female phonotactic responses to synthetic advertisement calls was tested in choice situations. Preferences based on differences in the linear rise-time of synthetic pulses depended on intensity and carrier frequency. When the carrier frequency was 1.1 kHz, simulating the low-frequency peak in the advertisement call, females preferred alternatives with slower rise-time pulses that differed by 5 ms at playback levels of 75 dB SPL and higher. A rise-time difference of 10 ms was discriminated at 65 dB SPL. When the carrier frequency was 2.2 kHz, simulating the high-frequency peak in the call, females discriminated a 5-ms difference in rise-time only at 85 dB SPL. Females showed no preference when the difference was 10 ms at lower playback levels. The difference in the thresholds (about 15–20 dB) for discriminating differences in rise-time at the two carrier frequencies was greater than the difference in behavioral thresholds for these two frequencies (about 10 dB). This result suggests that rise-time discrimination can be mediated solely by the neural channel mainly tuned to the low-frequency peak in the call. Females probably assess differences in rise-time by comparing the first few pulses of each call rather than by averaging over the entire call. Accepted: 30 March 1999     

A new cost-effective, selective and differential medium for the isolation of Cronobacter spp

The objective of the present study was to develop a new selective, differential and cost-effective medium (Kim and Rhee — KR-medium) for the isolation of Cronobacter spp. In this new medium, which contained salicin as a differential agent, Cronobacter spp. generated typical colonies with characteristic violet-colored centers surrounded by a transparent to opalescent border, and the growth of other microorganisms (40 strains) was inhibited or produced visually distinguishable colonies. Using healthy and heat- and desiccation-injured cells, the quantity of nutrients was adjusted to determine the optimal recovery rate, selectivity, differentiation and cost-effectiveness. Peptone and salicin concentrations were established as 10 and 8 g/L, respectively. The KR medium was then validated using salicin fermenting organisms, including Cronobacter spp. (52 strains), Enterobacter cloacae (50 strains) and Klebsiella pneumonia (10 strains) isolated from clinical and food specimens. All strains of Cronobacter spp. produced typical colonies and other salicin fermenting organisms were easily distinguishable from Cronobacter spp. with the exception of 2 E. cloacae strains. The verification of KR medium was carried out in powdered infant formula artificially inoculated with healthy, heat-injured, and desiccation-injured Cronobacter spp. and the expected typical colonies were appeared. The KR medium had a high specificity (98%) and sensitivity (100%), with no false-negative results. Moreover, we show that the cost of the KR medium is much lower than that of other selective and differential media. The use of the KR medium for the selective isolation of Cronobacter spp. in laboratories and food industry settings may therefore lessen the financial burden of Cronobacter spp. detection.     

长爪沙鼠脑底动脉Willis环变异缺失遗传特性分析及脑缺血模型高发群体的初步培育

目的研究长爪沙鼠脑底动脉Willis环遗传特性,并定向培育脑缺血高发种群。方法通过对5代定向培育的长爪沙鼠高发群动物共398只动物的右侧颈总动脉结扎模型进行观察,比较长爪沙鼠亲代与子代间脑底动脉Willis环的变异缺失类型,探求其遗传特性,并根据该遗传特性将Willis环后交通支缺失且前交通支缺失或细小的同类型的长爪沙鼠父母所生的子代雌雄个体配对繁殖,定向培育长爪沙鼠半脑缺血模型高发生率种群。结果当双亲的Willis环类型一致时,其子代大部分与其父母一致;而当双亲的Willis环类型不一致时,Willis环前交通支与母亲一致率为60.4%,前交通支与父亲的一致率为48.2%,两者的差异有显著性意义（P=0.015）。长爪沙鼠半脑缺血模型高发生率种群定向培育5代后,行单侧颈总动脉结扎时,一侧脑缺血造模成功率由F1代的40%提高到F5代的75%。结论长爪沙鼠脑底动脉Willis环变异有明显的遗传性,初步培育出了长爪沙鼠半脑缺血模型高发生率种群。     

Patterns of divergence of a large family of nodule cysteine‐rich peptides in accessions of Medicago truncatula

The nodule cysteine‐rich (NCR) groups of defensin‐like (DEFL) genes are one of the largest gene families expressed in the nodules of some legume plants. They have only been observed in the inverted repeat loss clade (IRLC) of legumes, which includes the model legume Medicago truncatula. NCRs are reported to play an important role in plant–microbe interactions. To understand their diversity we analyzed their expression and sequence polymorphisms among four accessions of M. truncatula. A significant expression and nucleotide variation was observed among the genes. We then used 26 accessions to estimate the selection pressures shaping evolution among the accessions by calculating the nucleotide diversity at non‐synonymous and synonymous sites in the coding region. The mature peptides of the orthologous NCRs had signatures of both purifying and diversifying selection pressures, unlike the seed DEFLs, which predominantly exhibited purifying selection. The expression, sequence variation and apparent diversifying selection in NCRs within the Medicago species indicates rapid and recent evolution, and suggests that this family of genes is actively evolving to adapt to different environments and is acquiring new functions.     

Don’t miss the forest for the trees! Evidence for vertical differences in the response of plant diversity to disturbance in a tropical rain forest

Ecological studies in tropical rain forests traditionally focus on trees above a threshold diameter at breast height (dbh), since ignoring plant species of the other structural compartments is believed to be an acceptable tradeoff between exhaustiveness and effectiveness. However, the consequences of missing species below a threshold dbh value have been largely neglected so far. We evaluated whether the response of species diversity of ≥10-cm dbh trees was similar to the response of other structural ensembles (namely treelets, saplings, and terricolous herbs) in a lowland tropical rain forest, to three disturbance regimes: natural gap dynamics (control), and selective logging with and without additional thinning. We studied forest vegetation composition and diversity in a 20-yr replicated field experiment comprising nine 1 ha permanent plots established in a semi-deciduous rain forest of the Congo Basin and equally distributed among the three treatments. Once corrected by stem density, species richness was similar between logged (20 years since logging) and untouched old-growth forest stands with respect of trees, but higher with respect of treelets. As disturbance intensity increased, species richness increased within sapling layers but decreased within herb layers, while species spatial turnover (beta diversity) increased in both cases. Regarding the parameters of the partitioned rarefaction curves and relative abundance distribution curves, no correlation was found between trees and any of the other structural compartments. Whilst tree and treelet species composition was similar among treatments, the understories still reflected past disturbance intensity, with a strong response of the sapling and herb layers. These results show that ecological studies based solely on tree layers (dbh ≥ 10 cm) are misleading because their response to disturbance cannot be used as a surrogate for the response of other structural ensembles. Long-lasting effects of anthropogenic disturbance on the sapling bank and the herb layer may durably influence the long-term forest dynamics. Since overstory but not understory plant communities have recovered from human disturbances 20 years after silvicultural operations, African tropical rain forest ecosystems may not be as resilient to selective logging as previously thought.     

Identification of the 5,5-dioxo-7,8-dihydro-6H-thiopyrano[3,2-d]pyrimidine derivatives as highly selective PDE4B inhibitors

A PDE4B subtype selective inhibitor is expected to have a wider therapeutic window than non-selective PDE4 inhibitors. In this Letter, two series of 7,8-dihydro-6H-thiopyrano[3,2-d]pyrimidine derivatives and 5,5-dioxo-7,8-dihydro-6H-thiopyrano[3,2-d]pyrimidine derivatives were evaluated for their PDE4B subtype selectivity using human PDE4B2 and PDE4D2 full length enzymes. To improve their PDE4B selectivity over PDE4D, we optimized the substituents on the pyrimidine ring and the side chain phenyl ring, resulting in several derivatives with more than 100-fold selectivity for PDE4B. Consequently, we identified 2-(3-chloro-4-methoxy-phenyl)-5,5-dioxo-7,8-dihydro-6H-thiopyrano[3,2-d]pyrimidine derivative 54 as a highly selective PDE4B inhibitor, which had potent hPDE4B inhibitory activity with an IC₅₀ value of 3.0 nM and 433-fold PDE4B selectivity over PDE4D.     

Development of a method to cryopreserve Greenshell mussel™ (Perna canaliculus) veliger larvae

Cryopreservation of larvae of Greenshell™ mussel Perna canaliculus, the most cultivated species in New Zealand, can provide flexibility for selective breeding programmes and enhance its global production. In this study, we set out to develop a reliable protocol for freezing D-stage larvae of Greenshell™ mussels that ensured long-term survival for successful rearing of thawed larvae in the hatchery. The effects of different combinations of cryoprotecting agents (CPA), varying CPA equilibration times, larval concentrations per straw as well as different larval development stages (48 h vs 72 h old) were evaluated by assessing the behavioural response (swimming activity, algal consumption), shell size and survival of larvae, up to 4 days post-thawing. The protocol yielding the best larval performances was a combination of the following CPA (final concentrations): 14% ethylene-glycol (EG) + 0.6 M trehalose (TRE) + 1% polyvinyl-pyrrolidone (PVP), prepared with Milli-Q water. Stocking densities ranging from 50,000 to 150,000 larvae per straw (0.25 mL) and a 20 min equilibration time gave the best results, while no significant differences in fitness were found between larvae cryopreserved at 48 h nor 72 h-old. Using the improved cryopreservation protocol, over 50% of previously cryopreserved D-larvae were able to survive after 4 days of rearing, compared with 65% in the unfrozen control. More importantly, about one third of thawed larvae were able to swim and feed, and to potentially develop further. These findings contribute to enhance the selective breeding programmes for this species.