Transport of bacterial inoculants through intact cores of two different soils as affected by water percolation and the presence of wheat plants

Abstract Water flow-innduced transport of Burkholderia cepacia strain P2 and Pseudomonas fluorescens strain R2f cells through intact cores of loamy sand and silt loam field soils was measured for two percolation regimes, 0.9 and 4.4 mm h⁻¹, applied daily during 1 hour. For each strain, transport was generally similar between the two water regimes. Translocation of B. cepacia , with 4.4 mm h⁻¹, did occur initially in both soils. In the loamy sand soil, no change in the bacterial distribution occurred during the experiment (51 days). In the silt loam, B. cepacia cell numbers in the lower soil layers were significantly reduced, to levels at or below the limit of detection. Transport of P. fluorescens in both soils also occurred initially and was comparable to that of B. cepacia . Later in the experiment, P. fluorescens was not detectable in the lower soil layers of the loamy sand cores, due to a large decrease in surviving cell numbers. In the silt loam, the inoculant cell distribution did not change with time. Pre-incubation of the inoculated cores before starting percolation reduced B. cepacia inoculant transport in the loamy sand soil measured after 5 days, but not that determined after 54 days. Delayed percolation in the silt loam soil affected bacterial transport only after 54 days. The presence of growing wheat plants overall enhanced bacterial translocation as compared to that in unplanted soil cores, but only with percolating water. Percolation water from silt loam cores appeared the day after the onset of percolation and often contained inoculant bacteria. With loamy sand, percolation water appeared only 5 days after the start of percolation, and no inoculant bacteria were found. The results presented aid in predicting the fate of genetically manipulated bacteria in a field experiment.     

Statistical analysis of algal and water quality data

Data on cyanobacteria (blue-green algae) are generallycollected on a reactive basis, frequently in responseto bloom events. Such data presents a biased andincomplete snapshot of water quality. This paper looksat two typical data sets for UK waters showing thatwhile statistics may be used to describe the data theyare of limited use in forecasting. Suggestions ofappropriate tests for small and sparse data sets aremade.     

Role of water receptor in the frog

To elucidate the role of the water receptor in the frog (Rana catesbeiana), reflex activities elicited by its excitation were studied. Application of tap water to the oral mucosa depressed the rhythmical movement of gorge (buccal) respiration, accompanied by an elevation of the inner pressure of the oral cavity (buccal pressure). Tonic reflex discharges were elicited in the nerves innervating the submental and submaxillary muscles, which close the nostrils, the pterygoid and the profound portion of the major masseter muscles, which produce a strong bite, and the geniohyoid and hyoglossus muscles, which elevate buccal pressure. These muscles, except for the pterygoid, also participate in the rhythmical movement of gorge respiration as expiratory muscles. Rhythmical movements in the minor masseter and sternohyoid muscles, which act as inspiratory muscles in gorge respiration, were depressed by the water stimulation of the oral mucosa. These findings indicate that the water receptor plays a role in the interruption of gorge respiratory movements, accompanied by an elevation of buccal pressure.     

Functional group contributions to the partitioning of phenols between liposomes and water

The temperature dependency of the partitioning of p-alkylphenols and p-halophenols has been determined between dimyristoyl phosphatidylcholine liposomes and 0.15 M NaCl. Partition coefficients increased as a function of temperature below the endothermic phase transition temperature (T_c) of the phospholipid but decreased above this temperature. The transfer process was found to be entropy-dominated below and enthalpy-dominated above the T_c, although large negative entropy changes were observed. Regular changes in the thermodynamic functions, partition coefficients and functional group free energies occurred as a function of the alkyl chain length or size of the halogen substituent below but not above the T_c. This has tentatively been attributed to increased phenol-phospholipid interaction at the higher temperatures. The partitioning of p-fluorophenol behaved in a manner expected of fluorinated compounds, yielding relatively low partition coefficients, but it produced an additional effect of markedly lowering the T_c of dimyristoyl phosphatidylcholine. Good correlations of the partition coefficients in liposomes with those in bulk organic solvents and with molecular size of the solute have been obtained.     

Theoretical investigations on circular and chain-like hydrogen bonded structures found in two crystal forms of α-cyclodextrin hexahydrate: Models for hydration and water clusters

Hydration of macromolecules and the structure of water of crystallization are not understood in detail because in these complex systems. H-atoms cannot be located and the hydrogen bonding schemes are not known. X-ray and neutron diffraction studies on a hydrated oligosaccharide, α-cyclodextrin 6H₂O, ((C₆H₁₀O₅)₆·6H₂O), crystals forms A and B, gave insight into the chain-like and circular arrangement of hydrogen bonds. In the circles, homodromic (unidirectional) and antidromic (counter-running) orientation of five to six hydrogen bounds is observed. PCILO calculations showed that homodromic circles and chains are approx. 8% per hydrogen bond more stable than antidromic circles, that the changes in electronic charges on H and O atoms are greater in homo than in antidromic systems and that the dipole moments are only approx. 3 D in the homodromic circles but 6–8 D in chain-like and antidromic arrangement. These results have been interpreted in terms of cooperative effect. Circular systems are considered as structural elements in hydration shells of macromolecules and in the assembly of ‘flickering’ water clusters.     

Interrelationships between water and cell metabolism in Artemia cysts X. Microwave dielectric studies

Artemia cysts are composed of an inner mass of about 4000 cells surrounded by an acellular shell. This system can undergo cycles of hydration-dehydration without viability loss, and is a useful model for the study of intracellular water. We have measured the relative permittivity (ε′) of these cysts as a function of water content over the frequency range 0.8–70 GHz. Detailed analysis of the data for cysts containing close to 1 g H₂O/g dry weight indicates that a significant fraction of the total water in this system exhibits dielectric behavior different from that of pure water: the distribution parameter (α) for the dispersion analyzed by the Cole-Cole equation deviates from zero, and the permittivity of cyst water appears to be significantly lower than that of pure liquid.     

Occurrence,properties and biological implications of the active uptake of water vapour from the atmosphere in Psocoptera

Water vapour absorption is shown to occur in 22 species of Psocoptera inhabiting diverse environments and representing all major groups of this insect order. Evidently the faculty is a common feature of the whole order and it seems not to be related to specific environmental conditions. For the first time water vapour uptake could be demonstrated in fully winged and flying insects. The critical equilibrium humidities vary considerably among different species ranging from 58 to 85% r.h. Marked interspecific differences are also observed in water loss and uptake rates but no clear correlation with habitat or systematic group is recognizable. The uptake rates of Psocoptera are among the highest of all arthropods investigated so far. From weight recordings with a sensitive microbalance it could be seen that continuous operation of the uptake mechanism is restricted to limited periods of time of less than 1 hr regardless of the water status of the animals. Initiation and termination of the uptake process are abrupt and continuous uptake proceeds at a constant rate at a given relative humidity. Uptake rates are humidity-dependent decreasing with falling relative humidity whereas the adjustment of the equilibrium level of body water is independent of ambient humidity. Equilibrium is maintained by intermittent operation of the uptake mechanism within ca. 3% of body water mass. The uptake mechanism exhibits marked sensitivity to starvation in most members of the Psocomorpha. Some features of the uptake process of Psocoptera are in close agreement with those of Mallophaga reflecting the close relationship between the two groups.     

中国蚌螨属支序分类分析(蜱螨亚纲:蚌螨科)

选择35个特征对我国蚌螨属15种的支序分析结果表明:蚌螨P-Ⅳ(胫节)端腹部的指状突是将它们聚集成两群的主要特征.今村蚌螨P-Ⅳ端腹部仅具有短矩,与外群最近,认为是我国的蚌螨属水螨中最原始的种类;雌螨前殖吸盘板的形态影响戊蚌螨亚属与多盘蚌螨亚属的种类聚类,由此推测可以将蚌螨P-Ⅳ端腹部的指状突与雌螨前殖吸盘板的形态也作为蚌螨亚属的区分特征.由于殖吸盘结构简单是祖征态之一,因此认为具有5对殖吸盘的邻近蚌螨比6对殖吸盘的厚蚌螨更原始.雌螨具有1对殖吸盘板的寄蚌螨亚属种类与沃蚌螨亚属种类在支序系统树中形成姊妹群,结果支持Vidrine 将沃蚌螨亚属从寄蚌螨亚属中分离的修订.