A Technique for Predicting the Solvent-Producing Ability of Clostridium acetobutylicum

Changes in colony morphology were associated with the degeneration of solvent-producing strains of Clostridium acetobutylicum. The most efficient solvent-producing strains gave rise exclusively to colonies with dense centers containing large numbers of spores. Many outgrowths of various morphologies developed from the perimeter of such colonies after several days of incubation. The most degenerate cultures did not produce solvents and gave rise to large diffuse colonies that did not contain spores. These diffuse colonies did not produce outgrowths. Intermediate colony types were also observed. These could be derived from liquid cultures that were relatively poor solvent producers or from the outgrowths of colonies of efficient solvent-producing strains. Some of these intermediate types produced spores but did so less frequently than the high-solvent-producing strains. The spores of the intermediate types could not be distinguished from those of the most efficient solvent producers on the basis of heat sensitivity. The relationship observed between colony morphology and solvent production provides a method for predicting the solvent-producing potential of C. acetobutylicum cultures.     

Use of the AO plate for immediate mandibular reconstruction in cancer patients

Free vascularized bone grafts have revolutionized mandibular reconstruction, yet their use in all mandibulectomy patients is not always necessary. A recently developed alternative to bony reconstruction has been the use of the AO reconstruction plate. We compared the use of the AO reconstruction plate with immediate free bone graft mandibular reconstruction in 31 patients. Reconstruction plates were used in 20 and immediate free bone grafts were used in 11 patients. The overall success rate for use of the plate was 15 of 20 (75 percent). There were 6 anterior reconstructions, of which only 2 (33 percent) were successful. This is opposed to 13 of 14 (93 percent) lateral reconstructions that were successful in lateral plate placements. There were 11 immediate composite free flaps: 4 iliac crest, 4 scapula, 2 fibula, and 1 composite radial forearm flaps. Six repairs were for anterior defects, and there were 5 full-thickness defects, 3 of which were in the anterior position. All 11 flaps were successful. In conclusion, we believe the reconstruction plates are a useful adjunct for mandibular replacement in the head and neck cancer patient but should be reserved for lateral defects. For anterior reconstructions, even in patients with locally advanced disease, free-tissue transfer of composite osteocutaneous flaps is the reconstructive method of choice.     

The site and mechanism of dioxygen reduction in bovine heart cytochrome c oxidase

The site and mechanism of dioxygen reduction in cytochrome c oxidase from bovine heart muscle have been investigated. The rate of cytochrome c2+ oxidation by O2 is shown to be affected by several factors: 1) pH, with optima at 5.65 and 6.0, 2) temperature between 0 and 29 degrees C, with E alpha = 13 kcal mol-1, 3) D2O exchange, with a reduction in rate of 50% or more at the pH optima, and 4) the addition of ethylene glycol or glycerol, which significantly lowers the rate. The extremely narrow (delta vCO approximately 4 cm-1) infrared stretch bands at approximately 1964 and approximately 1959 cm-1 for liganded CO are only slightly affected by factors 1-4 or by changes in the oxidation state of metals other than the heme alpha 3 iron. These results indicate a stable, unusually immobile O2 reduction site well-isolated from the external medium, a characteristic expected to be important for oxidase function. Precise stereochemical positioning of hydrogen donors adjacent to O2 liganded to heme alpha 3 iron can be expected in order to achieve the optimization of the time/distance relationships required for enzyme catalysis. These findings support a novel mechanism of O2 reduction via a hydroperoxide intermediate within a reaction pocket that experiences little change in conformation during the hydrogen and electron transfer steps.     

An ultrastructural investigation of Leishmania donovani infection in genetically resistant and susceptible mouse strains

Natural resistance to the growth of Leishmania donovani in mice is controlled by a gene (Lsh) which is expressed, in an unknown fashion, in macrophages. Early net growth rate of the parasite is much higher in mice strains bearing the susceptible allele (Lshs) than in resistant (Lshr) mice. Intracellular events occurring in the Kupffer cells during this period have been studied at the ultrastructural level. It was found that the number of dividing amastigotes per thin section of infected cell was approximately 10-fold greater in susceptible (B10.A SgSn) than in resistant (A/J) strains of mice, both 7 and 14 days following infection. These findings support the hypothesis that high natural resistance to leishmaniasis (Lshr) is expressed as a microbistatic effect, exerted within the parasitized macrophage of the host.     

Variation in heat shock proteins within tropical and desert species of poeciliid fishes

The 70-kilodalton heat shock protein (hsp70) family of molecular chaperones, which contains both stress-inducible and normally abundant constitutive members, is highly conserved across distantly related taxa. Analysis of this protein family in individuals from an outbred population of tropical topminnows, Poeciliopsis gracilis, showed that while constitutive hsp70 family members showed no variation in protein isoforms, inducibly synthesized hsp70 was polymorphic. Several species of Poeciliopsis adapted to desert environments exhibited lower levels of inducible hsp70 polymorphism than the tropical species, but constitutive forms were identical to those in P. gracilis, as they were in the confamilial species Gambusia affinis. These differences suggest that inducible and constitutive members of this family are under different evolutionary constraints and may indicate differences in their function within the cell. Also, northern desert species of Poeciliopsis synthesize a subset of the inducible hsp70 isoforms seen in tropical species. This distribution supports the theory that ancestral tropical fish migrated northward and colonized desert streams; the subsequent decrease in variation of inducible hsp70 may have been due to genetic drift or a consequence of adaptation to the desert environment. Higher levels of variability were found when the 30- kilodalton heat shock protein (hsp30) family was analyzed within different strains of two desert species of Poeciliopsis and also in wild-caught individuals of Gambusia affinis. In both cases the distribution of hsp30 isoform diversity was similar to that seen previously with allozyme polymorphisms.      

Prevalence of gallstones and gallbladder disease in Canadian Micmac Indian women.

The prevalence of gallstones and gallbladder disease was studied between October 1973 and June 1976 in Canadian Micmac Indian women aged 15 to 50 years in an inland rural community near Shubenacadie, NS. Of 132 women at risk 98 underwent cholecystography, 6 had a history of cholecystectomy (verified from hospital records) and 3 had cholecystectomy because of cholecystitis during the 3 years of the study. Of the 17 abnormal cholecystograms 10 showed radiolucent gallstones, and repeated studies documented gallstones in 6 of the 7 radiographs on which the gallbladder was not visualized. The prevalence of gallstones was found to be 211/1000, and that of gallbladder disease, 240/1000. The peak prevalence was at 30 to 39 years of age. The women with gallbladder disease were significantly more obese and of greater parity than those without gallbladder disease even when age was controlled. The Micmac Indian women of Nova Scotia appear to be at a much higher risk for the development of cholesterol gallstones and gallbladder disease than Caucasian women in Framingham, Massachusetts.     

Control of cell volume in the J774 macrophage by microtubule disassembly and cyclic AMP

We have explored the possibilities that cell volume is regulated by the status of microtubule assembly and cyclic AMP metabolism and may be coordinated with shape change. Treatment of J774.2 mouse macrophages with colchicine caused rapid microtubule disassembly and was associated with a striking increase (from 15-20 to more than 90 percent) in the proportion of cells with a large protuberance at one pole. This provided a simple experimental system in which shape changes occurred in virtually an entire cell population in suspension. Parallel changes in cell volume could then be quantified by isotope dilution techniques. We found that the shape change caused by colchicine was accompanied by a decrease in cell volume of approximately 20 percent. Nocodozole, but not lumicolchicine, caused identical changes in both cell shape and cell volume. The volume loss was not due to cell lysis nor to inhibition of pinocytosis. The mechanism of volume loss was also examined. Colchicine induced a small but reproducible increase in activity of the ouabain-sensitive Na(+), K(+)-dependent ATPase. However, inhibition of this enzyme/transport system by ouabain did not change cell volume nor did it block the colchicines-induced decrease in volume. One the other hand, SITS (4’acetamido, 4-isothiocyano 2,2’ disulfonic acid stilbene), an inhibitor of anion transport, inhibited the effects of colchicines, thus suggesting a role for an anion transport system in cell volume regulation. Because colchicine is known to activate adenylate cyclase in several systems and because cell shape changes are often induced by hormones that elevate cyclic AMP, we also examined the effects of cyclic AMP on cell volume. Agents that act to increase syclic AMP (cholera toxin, which activates adenylate cyclase; IBMX, and inhibitor of phosphodiesterase; and dibutyryl cyclic AMP) all caused a volume decrease comparable to that of colchicine. To define the effective metabolic pathway, we studied two mutants of J774.2, one deficient in adenylate cyclase and the other exhibiting markedly reduced activity of cyclic AMP-dependent protein kinase. Cholera toxin did not produce a volume change in either mutant. Cyclic AMP produced a decrease in the cyclase-deficient line comparable to that in wild type, but did not cause a volume change in the kinase- deficient line. This analysis established separate roles for cyclic AMP and colchicine. The volume decrease induced by cyclic AMP requires the action of a cyclic AMP-dependent protein kinase. Colchicine, on the other hand, induced a comparable volume change in both mutants and wild type, and thus does not require the kinase.     

Forging a path to mesoscopic imaging success with ultra-high field functional magnetic resonance imaging

Functional magnetic resonance imaging (fMRI) studies with ultra-high field (UHF, 7+ Tesla) technology enable the acquisition of high-resolution images. In this work, we discuss recent achievements in UHF fMRI at the mesoscopic scale, on the order of cortical columns and layers, and examine approaches to addressing common challenges. As researchers push to smaller and smaller voxel sizes, acquisition and analysis decisions have greater potential to degrade spatial accuracy, and UHF fMRI data must be carefully interpreted. We consider the impact of acquisition decisions on the spatial specificity of the MR signal with a representative dataset with 0.8 mm isotropic resolution. We illustrate the trade-offs in contrast with noise ratio and spatial specificity of different acquisition techniques and show that acquisition blurring can increase the effective voxel size by as much as 50% in some dimensions. We further describe how different sources of degradations to spatial resolution in functional data may be characterized. Finally, we emphasize that progress in UHF fMRI depends not only on scientific discovery and technical advancement, but also on informal discussions and documentation of challenges researchers face and overcome in pursuit of their goals.This article is part of the theme issue ‘Key relationships between non-invasive functional neuroimaging and the underlying neuronal activity’.