ALBERT

Notes: Abstract The existence of endosymbiotic sulfur-oxidizing chemoautotrophic and methanotrophic bacteria associating with marine mytilid mussels has previously been inferred by 16S rDNA analysis in Bathymodiolus puteoserpentis Von Cosel et al. 1994, a hydrothermal vent mussel from a site on the Mid-Atlantic Ridge. In mussels collected in June 1993, we found evidence of enzymes diagnostic of two distinct C1 assimilation pathways in this symbiosis. Assays for the utilization of radiolabelled methane and for immunodetection of methanol dehydrogenase were positive, indicating that oxidation and incorporation of this substrate are occurring in this symbiosis. Sulfide or thiosulfate had no detectable stimulatory effect on CO2 incorporation, and assays for the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO), an enzyme diagnostic for the Calvin–Benson cycle, were negative. RubisCO was detected in all samples examined by immunoblot analysis, indicating this enzyme is expressed in the B. puteoserpentis symbiosis. Stable isotope data showed that carbon isotope values were in agreement with previously reported values, and nitrogen isotope values were among the most depleted ever reported for bivalve symbioses. The carbon isotope values do not preclude the utilization of vent-derived methane. These data could be explained by the presence of two metabolically distinct bacterial symbionts or a Type X methanotrophic symbiont.

Notes: Abstract Growth of Methanobacterium formicicum strain MF was studied in pH-stat batch cultures and formatelimited chemostat cultures. The maxium rate of methanogenesis from formate occurred at pH 7.6 and 43°C and the maximum specific growth rate constant (μm) was 0.08 h-1. The K s and maximum growth yield (Y s max ) were 3.5 mM formate and 1.4 (g dry wt) mol01 formate respectively, and the maintenance coefficient (m) was calculated as 6.8 mmol formate (g dry wt)-1 h-1. The efficiency of electron transport phosphorylation during formate metabolism assuming Y ATP of 10.5 g mol-1 was about 20%. The specific activities of hydrogenase and formate dehydrogenase increased slightly with dilution rate.

Notes: Summary The clearance of chlordiazepoxide from the systemic circulation was studied in 20 subjects which included 15 patients with alcoholic hepatitis and 5 normal volunteers. The half-life for the appearance of the drug in the systemic circulation was found to increase exponentially with age (r=0.73, P〈0.0005) and was independent of the presence of alcoholic hepatitis. The metabolic clearance of chlordiazepoxide was significantly lower in the patients than in the normal subjects (7.6 compared to 13.8 ml/kg-h, P〈0.005). Linear regression analysis revealed a significant correlation between clearance and albumin (r=0.77, P〈0.00005). However, the predictive value of this relationship was shown to be minimal. Multiple regression analysis produced only a slight improvement in the correlation when both albumin and lactate dehydrogenase were used as variables (r=0.83, P〈0.00005). In six of the patients, a second clearance study was conducted three weeks following their initial one. All repeat subjects showed improvement both clinically and as reflected by their laboratory tests for liver injury, but there was not a significant change in their clearance of chlordiazepoxide. Multiple regression analysis of the clearance data on the initial and repeat subjects showed a significant correlation between clearance and the variables age, albumin, and lactate dehydrogenase (r=0.91, P〈0.0025). This relationship suggests that over a short period of time (where age can be considered constant) changes in albumin and lactate dehydrogenase could be potentially useful in predicting clearance changes in a single individual.

Notes: Robinson, J. M. 1988. Does O2 photoreduction occur within chloroplasts in vivo? -Physiol. Plant. 72: 666–680.This discussion reviews evidence supporting the hypothesis that within intact chloroplasts in vivo, molecular O2 may serve as an alternative Hill oxidant (electron acceptor) on the reducing side of Photosystem I. Depending upon the availability of Hill oxidants such as NADP+ and NO−2, there is the potential within intact plastids in vivo, for photolytically derived reducing equivalents to reduce O2 to O−2 and H2O2 (the Mehler reaction). In chloroplasts of healthy tissues, the products of photosyn-thetic O2 reduction O−2 and H2O2) are rapidly removed by superoxide dismutase (EC 1.15.1.1) and L-ascorbate peroxidase (EC 1.11.1.11) to prevent toxicity. The presence of these two enzymes within chloroplasts in vivo reflects the potential for linear (non-cyclic) photosynthetic electron transport systems to draw upon molecular O2 as a terminal oxidant. In the intact plastid, O2 may act as an electron acceptor in the place of any other physiological Hill oxidant, e.g., NADP+, NO−2, and, presumably, oxidized thioredoxin. Under aerobic, physiological conditions, photo reduced ferre-doxin (Fdred), and/or reduced flavoprotein enzymes, e.g., ferredoxin:NADP+ oxidoreductase (EC 1.18.1.2), can donate electrons to O2; this reductive reaction appears to be non-enzymatic, but it is rapid. Stated from another viewpoint, O2 may serve as a Hill oxidant to support some linear electron flow when reductant supplies are in excess of reductant demands. For example, there are nitrogen assimilatory sites in the chloroplast, i.e., ferredoxin-nitrite reductase (NiR; EC 1.7.7.1) and glutamate synthase (ferredoxin) (GOGAT; EC 1.4.7.1), to which Fdred is allocated as reductant. Because NADH:nitrate reductase (NR; EC 1.6.6.1) is the rate limiting step of nitrogen assimilation, and, because NiR and GOGAT activities are in excess of NR activities by a factor of 2 or more, then an excess of unreacted Fdred could accumulate. Alternatively, the allocated Fdred would reduce the excess NiR and GOGAT sites, but the excess of reduced enzymes would not have substrates (e.g., NO−2, glutamine, and α-ketoglutarate) with which to react. Therefore, if ‘excess’ NiR and GOGAT binding sites were not employed, the available excess Fdred, and/or the reduced NiR and GOGAT proteins, would be susceptible to oxidation by O2. The resulting O2 photoreduction could account for nearly all of the observed in vivo Mehler type reactions. In vivo, apparent foliar O2 photoreduction occurs simultaneously with maximal CO2 photoassimilation, and, in high light, average rates have been determined by direct measurement to range from 10 to 40 μmol O2 consumed (mg Chl)−1 h−1. Therefore O2 reduction would support a low rate of linear (non-cyclic) electron flow which, in turn, could maintain a low, but significant rate of ATP production. However, there is not total agreement among researchers that the physiological role of O2 is that of serving as an alternative Hill oxidant in order to recycle unutilized Fdred or other photoreduced proteins. Also, there continues to be considerable controversy on whether or not O2 reduction supports significant photosynthetic phosphorylation. The total process of O2 photoreduction, and its physiological role(s), requires much more study before absolute functions can be assigned to O2 terminated, linear electron transport.〈section xml:id="abs1-1"〉〈title type="main"〉SummaryMolecular O2 possesses the physico-chemical properties that permit this molecule to serve as an alternative Hill oxidant within chloroplasts in vivo. Additionally, the physical and physiological properties within the chloroplast in vivo favor the potential for O2 to serve as an electron acceptor on the reducing side of Photosystem I. This may reflect an important ‘fail-safe mechanism’ which prevents over-reduction of linear photosynthetic electron transport chain proteins. This review has focused on the possibility that unutilized Fdred and/or other non-utilized, reduced plastid enzymes (e.g., NiR) may be electron donors to O2. It is hypothesized that this oxidation ultimately would be reflected as an in vivo Mehler reaction. However, it remains for future studies to establish without doubt, that in vivo, photoreduced chloroplast enzyme proteins can utilize O2 as a terminal electron acceptor.Further, that O2 photoreduction supports a significant level of photophosphorylation in vivo remains to be firmly established. Certainly, considerable evidence, gained with experiments utilizing isolates of intact chlo-roplasts and reconstituted chloroplast systems, supports the hypothesis that O2-terminated linear electron transport has the potential to support high rates of ATP production. However, in vivo studies e.g., with intact leaf tissues, which actually quantitate the relationship between O2 photoreduction and associated ATP production have not been conducted. These will be difficult experiments to perform, because, in vivo, it will be difficult to separate photosynthetic ATP production mediated by O2 from ATP production mediated by those other, more predominant Hill oxidants (e.g., NADP+, NO−2). Also, it continues to be a possibility that it is cyclic, and not pseudocyclic photophosphorylation that provides additional ATP to support photosynthetic cell metabolism. To establish beyond doubt that an in vivo role of the Mehler reaction is that of supplying ‘additional ATP’, remains for considerable future study.

Notes: Mixing of fluids at fracture intersections was examined using both a series of plexiglass models and a two-dimensional, finite-element, discrete fracture model. The physical laboratory models included 12 models having two continuous, fully intersecting fractures with different intersection angles and apertures, a single model consisting of a single continuous fracture offsetting a second fracture, and a fracture system model consisting of parallel fractures in two intersecting sets. The plexiglass model results indicated essentially no mixing occurred in the fully intersecting fracture models when the apertures were equal. Mixing was found to be dependent only upon the relative size of the inlet and outlet fractures even with multiple intersections.For transport of a conservative solute in a discontinuous, random, discrete fracture system, the numerical model used the mixing algorithm for fracture intersections, developed from the physical model study. At each four-way intersection, a novel approach was used to uncouple and recouple the nodal points to ensure the proper assignment of concentrations to each fracture element. Using the laboratory-determined mixing algorithm, the numerical model demonstrated that more longitudinal and less lateral dispersion takes place than when complete mixing at fracture intersections is assumed. In addition, more longitudinal transport takes place in discontinuous than in continuous fracture systems. These findings indicate that contaminants migrating through fractured media, where the fracture walls are not in contact, will not be dispersed and diluted to the extent that previous numerical models have predicted; hence, the contaminant will be discharged to the biosphere in much greater concentration than expected.

Notes: SUMMARY. A simple, inexpensive sample holder was developed to permit delicate biological materials (faecal pellets) to be decomposed in aquatic environments and thereafter to be processed by dehydration and critical point drying procedures. Part of the holder itself is used to mount the sample onto specimen studs. Delicate materials are therefore never subjected to physical damage during handling at any stage of their processing for scanning electron microscopy.

Notes: SUMMARY. Gammarus lacustris limnaeus Smith was fed decomposed autumnshed leaves of maple (Acer saccharum Marsh.) and poplar (Populus tremuloides Michx.). Faecal pellets were collected at various time intervals after egestion and examined under a light and a scanning electron microscope. Nearly all the faecal pellets collected up to a period of about 7 h after egestion possessed a thin, tightly-fitting peritrophic membrane while those that had been outside the gut of the animal for a longer time lacked a peritrophic membrane. Presumably, after egestion faecal pellets swell because of absorption of water leading to eventual rupture and loss of the membrane. The surface of newly extruded pellets is devoid of microbes and microbes seem to play a very insignificant role in the loss of peritrophic membrane from the pellets.

Notes: Velocity analysis of reflection seismic data has increased in popularity with petroleum exploration personnel to such an extent that it now constitutes a significant tool in the routine digital processing program. One drawback to such an analysis is its computational cost, resulting from the numerous mathematical calculations required by a digital computer to extract comprehensive velocity information.The subject algorithm affords a computational cost saving of approximately one order of magnitude over a straightforward summational type velocity analysis with little sacrifice in accuracy. The utility of the algorithm is demonstrated on some Offshore Louisiana seismic data and a comparison of the results reveals that they are almost identical with a conventional velocity analysis.The algorithm is based on the concept that a normal-moveout pattern of time shifts may be accurately applied over a considerable span of zero-offset times to a CDP trace gather, rather than only at a single zero-offset time. With each application however, the rms-velocity associated with the moveout pattern is different. A specific relationship which associates an rms-velocity with a zero-offset time for the same moveout time delay pattern is approximated by numerical simulation studies on a digital computer.