Mechanical damage to Gram-negative bacteria by surface plating with the Drigalski-spatula technique

Colony counting by spreading bacterial suspensions on plating media by various techniques is of general concern. Comparative studies between hand plating (Drigalski-spatula technique) for different time intervals and spiral plating resulted in significant differences in colony counts. Lower counts of Gram-negative bacteria were obtained by using hand plating for more than 10 s, compared with short time hand plating (5 s) or spiral plating. Colony counting of Gram-positive bacteria showed no differences between both techniques. Further characterisation of Escherichia coli cells spread with the Drigalski-spatula technique by electron microscopy revealed a large number of damaged cells compared to control samples. The data clearly shows that the mechanical forces during hand plating are sufficient to damage E. coli cells.     

Interaction of thyroxine and estrogen on the expression of estrogen receptor alpha, cholecystokinin, and preproenkephalin messenger ribonucleic acid in the limbic-hypothalamic circuit

To study thyroid hormone and estrogen interactions in the central nervous system (CNS), the expression of estrogen sensitive genes was examined within the limbic-hypothalamic circuit. Estrogen up-regulates the expression of reproductively relevant neuropeptide messenger RNAs (mRNAs) encoding cholecystokinin (CCK) and enkephalin, peptides that stimulate lordosis. Estrogen down-regulates the expression of the estrogen receptor alpha (ER alpha) mRNA in the nuclei of the circuit. We examined the possibility that thyroid hormone treatment would block the estrogen modulation of these messages. Estradiol benzoate (EB), EB + thyroxine (T4), T4, or oil were administered to ovariectomized, adult female rats for 10 days. Isotopic in situ hybridization histochemistry revealed that within the limbic-hypothalamic nuclei, levels of CCK and preproenkephalin (PPE) mRNA levels were significantly higher in EB and EB + T4-treated animals compared with T4 or oil-treated animals. ER alpha mRNA levels were low in EB treated animals, elevated in T4 or oil-treated animals and further elevated in EB + T4-treated animals. In summary, T4 treatment had neither an independent nor an antagonistic effect on estrogen induced expression of CCK or PPE mRNA in the circuit. However, T4 did prevent the normal estrogenic decrease of ER alpha mRNA levels in the nuclei of the limbic-hypothalamic circuit.     

Natural and unnatural silks

Natural silk is an important biopolymer with huge potential as it combines superb mechanical properties with environmentally sensitive production methods. Native silk dope taken straight from the gland can easily and without chemical assistance be drawn into strong fibres. Artificial silk fibres, on the other hand, rely on spinning dopes typically ‘reconstituted’ from natural silk fibres by strong chaotropic agents. Such fibres do not form readily, and often require chemical post-spin treatment for stabilisation. In addition these fibres tend to be brittle, and so far have been unable to match native fibres. Here we present novel rheometric data to argue that native and reconstituted silkworm silk dope differ in kind, not just in degree. While native silks behave like typical molten polymers, reconstituted silks do not. We conclude that rheology provides a powerful tool in the quest to learn from the Nature's polymer fibre technology.     

Amino acid profiles and liposomes: Their role as chemosensory information carriers in the marine environment

Yellowfin tuna enhance their hunting success in the vast pelagic environment by using their sense of smell to detect intact (uninjured) prey that are beyond visual range. However, the olfactory cues that tuna use would normally face huge and rapid dilution in the open ocean. We demonstrate that these prey odors are complexed within biologically derived lipid structures that probably delay the dilution of the amino acids to subthreshold concentrations and provide persistent arousal and search cues for the tuna. This may be the first demonstration of an extracorporeal biological function for liposomes. Tuna may also form chemical search images to maximize feeding efficiency. We demonstrate that the amino acid profiles of various prey species are consistent over time and between schools, which makes the formation of search images feasible.     

Nanostructured polymer blends: Synthesis and structure

Nanostructured polymer blends prepared via anionic ring opening polymerizations of cyclic monomers in the presence of a pre-made polymer melt exhibit a number of special properties over traditional polymer blends and homopolymers. Here, we report on a simple and versatile method of in situ polymerization of macrocyclic carbonates in the presence of a maleic anhydride polypropylene (mPP) matrix and a surface-active compatibilizer (i.e. PC grafted onto a mPP backbone generated in situ) to yield a micro- and nanostructured polymer blends consisting of a polycarbonate (PC) minor phase, and a polypropylene (PP) major phase. By varying the processing conditions and concentration of the macrocyclic carbonate it was possible to reduce the size of the PC dispersions to an average minor diameter of 150 nm. NMR and TEM characterizations indicate that the PC dispersions do not influence crystal content in the PP phase. Overall, the results point to a simple strategy and versatile route to new polymeric materials with enhanced benefits.     

The influence of oxygen on the differentiation of temperature-sensitive and temperature-insensitive Lactococcus lactis subsp. cremoris starter strains

The differentiation of temperature-insensitive and temperature-sensitive strains of Lactococcus lactis subsp. cremoris by using a modified sodium-β-glycerophosphate/milk medium is described (temperature-insensitive strains are defined as those that continue to grow at 38°C and temperature-sensitive strains as those that do not grow, or grow poorly, at 38°C). The physiological basis for the differentiation assay was examined by using L. lactis subsp. cremoris strains 2146 (temperature-insensitive) and 2182 (temperature-sensitive) as test strains. After aerobic incubation on the medium, strain 2146 formed uniform colonies, 0·5 mm in diameter, while strain 2182 formed larger colonies, 1·0–1·5 mm in diameter. The differential was dependent on the medium constituents, on an aerobic gas phase, and on the effects of H₂O₂ generated within the colonies. The addition of 0·5% (w/v) pyruvate to the medium facilitated the growth of colonies of strain 2146 to 3-mm diameter, while the colony size of strain 2182 remained at 1-mm diameter, and thus the colony-size differential between strains was reversed. The growth of both strains was inhibited at 0·4–0·8% air saturation during suspension culture in sodium-β-glycerophosphate/milk medium. The inclusion of catalase in the cultures overcame the growth inhibition. There was no observable difference between the two strains in their oxygen sensitivity or NADH oxidase/peroxidase enzymology.     

The restricting effects of awareness: A paradox and explanation.

Ss were shown tachistoscopically-presented word stimuli to test the distinction between the perceptual processes of registration (what could be called physiological or sensory threshold) and awareness (or the cognitive threshold). The presentation consisted of a stimulus word followed by series of words associated to the stimulus word either in terms of meaning or structural resemblance. Recall of words presented subliminally or supraliminally was facilitated with degree of awareness of actual stimulus word; with greater awareness of the word, associational recall was for words that structurally resembled S word; without awareness, recall was determined by associative meaning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)