The genes for butanol and acetone formation in Clostridium acetobutylicum ATCC 824 reside on a large plasmid whose loss leads to degeneration of the strain

Degeneration is the process whereby Clostridium acetobutylicum ATCC 824 loses the capacity to produce acetone and butanol after repeated vegetative transfers or in continuous culture. Two degenerate mutants (M5 and DG1) of C. acetobutylicum ATCC 824 do not contain the four genes (ctfA, ctfB, adc, and aad) for acetone and butanol formation. Strain ATCC 824 contains a 210-kb plasmid (pSOL1) which is absent in M5 and DG1. pSOL1 carries the four acetone and butanol formation genes. A restriction map of pSOL1 was constructed by using ApaI, SmaI, SstII, and NarI digestions. M5 and DG1 could be complemented for acetone and butanol formation by expressing the corresponding genes (ctfA, ctfB, and adc for acetone; aad for butanol) on the plasmid. Degeneration of this strain thus appears to be the result of pSOL1 loss.     

Assessment of different techniques for quantification of α-Al(FeMn)Si and β-AlFeSi intermetallics in AA 6xxx alloys

During homogenisation of AA 6xxx aluminium alloys, the platelike β-AlFeSi intermetallic phase will transform to a less Si-rich and more spheroidised α-Al(FeMn)Si phase which is more favourable for extrusion. In this study, several quantitative methods, which determine the relative volume fraction of α-Al(FeMn)Si and β-AlFeSi, are compared and an assessment of each method is made. The methods used are optical microscopy, scanning electron microscopy (SEM) in combination with electron dispersive X-ray (EDX) using polished samples, and X-ray diffraction (XRD) on intermetallics, extracted through selective dissolution of the Al matrix. The highest accuracy is obtained by using SEM/EDX analysis and applying two criteria.     

Mutagenic activity in the rivers Rhine and Meuse in The Netherlands

Several water samples of the rivers Rhine and Meuse have been tested for mutagenic activity in the Ames Salmonella/microsome assay and a fluctuation assay. Samples were taken at places where the rivers enter The Netherlands and at several downstream locations relevant to drinking water supplies. For the Rhine this included samples of each of the river-branches Waal, Lek and IJssel. Before testing, all water samples were concentrated by adsorption on XAD-resins and subsequent elution with dimethylsulfoxide.The results obtained clearly show that all water samples derived from the river Rhine and its branches contain mutagenic activity. Positive Ames test results showing dose—response relations were observed primarily with strain TA 98 after metabolic activation (rat liver microsomal enzymes). In contrast to this, little or no mutagenic activity was detected in samples from the river Meuse. This indicated that, with the methods used, the overall mutagenic activity of the river Meuse was at least 10 times below that of the river Rhine. In the fluctuation assay, using the same bacterial strains, the river water concentrates could not be tested as such. However, after appropriate dilution of the dimethylsulfoxide with distilled water, this assay proved to be about 10–15 times more sensitive than the Ames test. The significance of these results with respect to human health is briefly discussed.     

Structure and Replication of yDNA: A Novel Genetic Set Widened by Benzo‐Homologation

In a functioning genetic system, the information‐encoding molecule must form a regular self‐complementary complex (for example, the base‐paired double helix of DNA) and it must be able to encode information and pass it on to new generations. Here we study a benzo‐widened DNA‐like molecule (yDNA) as a candidate for an alternative genetic set, and we explicitly test these two structural and functional requirements. The solution structure of a 10 bp yDNA duplex is measured by using 2D‐NMR methods for a simple sequence composed of T–yA/yA–T pairs. The data confirm an antiparallel, right‐handed, hydrogen‐bonded helix resembling B‐DNA but with a wider diameter and enlarged base‐pair size. In addition to this, the abilities of two different polymerase enzymes (Klenow fragment of DNA pol I (Kf) and the repair enzyme Dpo4) to synthesize and extend the yDNA pairs T–yA, A–yT, and G–yC are measured by steady‐state kinetics studies. Not surprisingly, insertion of complementary bases opposite yDNA bases is inefficient due to the larger base‐pair size. We find that correct pairing occurs in several cases by both enzymes, but that common and relatively efficient mispairing involving T–yT and T–yC pairs interferes with fully correct formation and extension of pairs by these polymerases. Interestingly, the data show that extension of the large pairs is considerably more efficient with the flexible repair enzyme (Dpo4) than with the more rigid Kf enzyme. The results shed light on the properties of yDNA as a candidate for an alternative genetic information‐encoding molecule and as a tool for application in basic science and biomedicine.     

Declining sperm counts in the United States? A critical review

PURPOSE: Recent reports suggest declining sperm counts in the United States. These reports did not include all available data and did not account for geographic variations noted in prior studies. We examined all available data on U.S. sperm counts and evaluated whether geographic variations account for the decline suggested. MATERIALS AND METHODS: We reviewed all 29 U.S. studies from 1938 to 1996 reporting manually counted semen analyses of 9,612 fertile or presumably fertile men. We determined mean sperm concentrations by geographic location with weighted analysis of variance, and assessed any changes with time by linear regression analysis. RESULTS: Mean sperm concentrations from New York were significantly higher than from all other U.S. cities (98.6 versus 71.6 x 10(6) sperm per cc, respectively, p = 0.006). There has been no statistically significant change with time for mean sperm concentrations reported from New York (p = 0.49) or from U.S. cities other than New York (p = 0.62). Analysis without separating by location revealed a decline (p = 0.047). CONCLUSIONS: Sperm concentrations are highest in New York compared to other U.S. cities. When accounting for this geographic difference and examining all available data, there appears to be no significant change in sperm counts in the U.S. during the last 60 years. Further studies addressing the causes of geographic variations are needed.     

Responses to the sensory properties of fat of neurons in the primate orbitofrontal cortex

The primate orbitofrontal cortex is a site of convergence of information from primary taste, olfactory, and somatosensory cortical areas. We describe the responses of a population of single neurons in the orbitofrontal cortex that responds to fat in the mouth. The neurons respond, when fatty foods are being eaten, to pure fat such as glyceryl trioleate and also to substances with a similar texture but different chemical composition such as paraffin oil (hydrocarbon) and silicone oil [Si(CH3)2O)n]. This is evidence that the neurons respond to the oral texture of fat, sensed by the somatosensory system. Some of the population of neurons respond unimodally to the texture of fat. Other single neurons show convergence of taste inputs, and others of olfactory inputs, onto single neurons that respond to fat. For example, neurons were found that responded to the mouth feel of fat and the taste of monosodium glutamate (both found in milk), or to the mouth feel of fat and to odor. Feeding to satiety reduces the responses of these neurons to the fatty food eaten, but the neurons still respond to some other foods that have not been fed to satiety. Thus sensory-specific satiety for fat is represented in the responses of single neurons in the primate orbitofrontal cortex. Fat is an important constituent of food that affects its palatability and nutritional effects. The findings described provide evidence that the reward value (or pleasantness) of the mouth feel of fat is represented in the primate orbitofrontal cortex and that the representation is relevant to appetite.