Sum of fears among intraguild predators drives the survival of green sea turtle (Chelonia mydas) eggs.

Ecologists have long theorized that apex predators stabilize trophic systems by exerting a net protective effect on the basal resource of a food web. Although experimental and observational studies have borne this out, it is not always clear what behavioural mechanisms among the trophically connected species are responsible for this stability. Fear of intraguild predation is commonly identified as one such mechanism in models and mesocosm studies, but empirical evidence in natural systems remains limited, as the complexity of many trophic systems renders detailed behavioural studies of species interactions challenging. Here, we combine long-term field observations of a trophic system in nature with experimental behavioural studies of how all the species in this system interact, in both pairs and groups. The results demonstrate how an abundant, sessile and palatable prey item (sea turtle eggs, Chelonia mydas) survives when faced by three potential predators that all readily eat eggs: an apex predator (the stink ratsnake, Elaphe carinata) and two mesopredators (the brown rat, Rattus norvegicus, and kukri snake, Oligodon formosanus). Our results detail how fear of intraguild predation, conspecific cannibalism, habitat structure and territorial behaviour among these species interact in a complex fashion that results in high egg survival.

Biochemical Characterization and Crystal Structure of a Novel NAD+-Dependent Isocitrate Dehydrogenase from Phaeodactylum tricornutum.

The marine diatom Phaeodactylum tricornutum originated from a series of secondary symbiotic events and has been used as a model organism for studying diatom biology. A novel type II homodimeric isocitrate dehydrogenase from P. tricornutum (PtIDH1) was expressed, purified, and identified in detail through enzymatic characterization. Kinetic analysis showed that PtIDH1 is NAD+-dependent and has no detectable activity with NADP+. The catalytic efficiency of PtIDH1 for NAD+ is 0.16 µM-1·s-1 and 0.09 µM-1·s-1 in the presence of Mn2+ and Mg2+, respectively. Unlike other bacterial homodimeric NAD-IDHs, PtIDH1 activity was allosterically regulated by the isocitrate. Furthermore, the dimeric structure of PtIDH1 was determined at 2.8 Å resolution, and each subunit was resolved into four domains, similar to the eukaryotic homodimeric NADP-IDH in the type II subfamily. Interestingly, a unique and novel C-terminal EF-hand domain was first defined in PtIDH1. Deletion of this domain disrupted the intact dimeric structure and activity. Mutation of the four Ca2+-binding sites in the EF-hand significantly reduced the calcium tolerance of PtIDH1. Thus, we suggest that the EF-hand domain could be involved in the dimerization and Ca2+-coordination of PtIDH1. The current report, on the first structure of type II eukaryotic NAD-IDH, provides new information for further investigation of the evolution of the IDH family.

Comparison Among Five Eucalyptus Species Based on Their Leaf Contents of Some Primary and Secondary Metabolites.

BACKGROUND: Eucalyptus belongs to the Myrtaceae family. It is the most planted hardwood forest crop worldwide, representing a global renewable resource of fiber, pharmaceuticals and energy. OBJECTIVE: To compare the five species, E. maidenii, E. robusta, E. citriodora, E. tereticornis and E. camaldulensis, seeking for the richest source of nutrients and pharmaceuticals. METHODOLOGY: Eucalyptus samples were subjected to some chemical determinations for both primary and secondary metabolites to verify their nutritional and pharmaceutical importance related to different extracts. GC-MS analysis was applied to detect the presence of some individual phenolic constituents in their leaves. RESULTS: E. robusta recorded the maximum contents of carbohydrates (40.07%) and protein (31.91%). While E. camaldulensis contained the highest contents of total phenolic compounds (46.56 mg/g), tannins (40.01 mg/g) and antioxidant activities assayed by the phosphomolybednum method (57.60 mg/g), followed by E. citridora. However, E. tereticornis exhibited the highest reducing power ability (151.23 mg/g). The GC-MS highlighted 20 phenolic constituents and antioxidants which varied in their abundance in Eucalyptus leaves, 8 individual phenolics (hydroquinone, hesperitin, pyrogallol, resorcinol, protocatechuic acid, naringenin, chlorogenic acid and catechin) were maximally recorded with E. camaldulensis and secondly, with E. citridora in case of at least 5 components. Nevertheless, gallic and quinic acids were more abundant in the leaves of E. tereticornis, which may explain its high corresponding reducing powers. CONCLUSION: Acetone-water combination has enhanced phenolics extraction from Eucalyptus tissues. This is the first report aiming to compare between the aforementioned Eucalyptus species highlighting either their nutritional or medicinal importance.

Comparative effects of some extraction solvents on the antimicrobial activity of Eucalyptus camaldulensis leaf, bud, capsule and seed crude extracts.

Well diffusion method was used to evaluate the antibacterial activity of Eucalyptus camaldulensis, while the antifungal effect was assessed by calculating the reduction percent in the radial growth of mycelia. The inhibition zones exerted by E. camaldulensis crude extracts varied significantly (p ≤ 0.01). The capsule crude extract (acetone 30%) highly inhibited the growth of Acinetobacter baumannii (35 mm clear zone). The highest antifungal activity was against Rhizopus stolonifer with a reduction percent in its radial growth reached to 96%. The bacterial MICs ranged from 20 to 0.5 mg/mL against Escherichia coli and Bacillus subtilis respectively. The MIC values for fungi were between 18 mg/mL (Mucor sp.) and 4 mg/mL (R. stolonifer). Both type and concentration of the solvent greatly affected the antimicrobial potentials of E. camaldulensis. The empty capsule and bud of E. camaldulensis are recognized for the first time as potentially natural resources of effective antimicrobial agents.

Biochemical Characterization and Complete Conversion of Coenzyme Specificity of Isocitrate Dehydrogenase from Bifidobacterium longum.

Bifidobacterium longum is a very important gram-positive non-pathogenic bacterium in the human gastrointestinal tract for keeping the digestive and immune system healthy. Isocitrate dehydrogenase (IDH) from B. longum (BlIDH), a novel member in Type II subfamily, was overexpressed, purified and biochemically characterized in detail. The active form of BlIDH was an 83-kDa homodimer. Kinetic analysis showed BlIDH was a NADP⁺-dependent IDH (NADP-IDH), with a 567- and 193-fold preference for NADP⁺ over NAD⁺ in the presence of Mg(2+) and Mn(2+), respectively. The maximal activity for BlIDH occurred at 60 °C (with Mn(2+)) and 65 °C (with Mg(2+)), and pH 7.5 (with Mn(2+)) and pH 8.0 (with Mg(2+)). Heat-inactivation profiles revealed that BlIDH retained 50% of maximal activity after incubation at 45 °C for 20 min with either Mn(2+) or Mg(2+). Furthermore, the coenzyme specificity of BlIDH can be completely reversed from NADP⁺ to NAD⁺ by a factor of 2387 by replacing six residues. This current work, the first report on the coenzyme specificity conversion of Type II NADP-IDHs, would provide better insight into the evolution of NADP⁺ use by the IDH family.