Whole-plant gas exchange responses of Spartina alterniflora (Poaceae) to a range of constant and transient salinities

A two-chamber-system was used to study whole-plant gas exchange responses of Spartina alterniflora to long-term and transient salinity treatments over the range of 5 to 40 ppt NaCl. Lower photosynthetic rates, leaf water vapor conductances, belowground respiration rates, and higher aboveground respiration rates in plants adapted to 40 ppt NaCl were observed. Area-specific leaf weight increased with salinity, although the salt content of leaf tissues did not. A reduced rate of gross photosynthesis and higher aboveground respiration rate in 40-ppt NaCl plants significantly lowered the net whole-plant CO₂ gain below that of 5-ppt NaCl plants, while the net CO₂ gain of 25-ppt NaCl plants was intermediate. Within 6 hr of increasing the salinity of 5- and 25-ppt NaCl plants by 20 and 15 ppt NaCl, S. alterniflora responded by reducing leaf water vapor conductance, which in turn reduced the photosynthetic rate. This response was reversed by returning the plants to their original salinity, which indicates that S. alterniflora adjusts water loss and gas exchange in response to transient salinity stress by regulating stomatal aperture. On the other hand, decreasing salinity of the growth media of plants cultured at 25 and 40 ppt NaCl had little or no effect on gas exchange characteristics. This suggests that S. alterniflora adapts to constant salinity through fixed, salinity-dependent structural modifications, such as stomatal density.     

Polymorphic Admixture Typing in Human Ethnic Populations

A panel of 257 RFLP loci was selected on the basis of high heterozygosity in Caucasian DNA surveys and equivalent spacing throughout the human genome. Probes from each locus were used in a Southern blot survey of allele frequency distribution for four human ethnic groups: Caucasian, African American, Asian (Chinese), and American Indian (Cheyenne). Nearly all RFLP loci were polymorphic in each group, albeit with a broad range of differing allele frequencies (δ). The distribution of frequency differences (δ values) was used for three purposes: (1) to provide estimates for genetic distance (differentiation) among these ethnic groups, (2) to revisit with a large data set the proportion of human genetic variation attributable to differentiation within ethnic groups, and (3) to identify loci with high δ values between recently admixed populations of use in mapping by admixture linkage disequilibrium (MALD). Although most markers display significant allele frequency differences between ethnic groups, the overall genetic distances between ethnic groups were small (.066–.098), and <10% of the measured overall molecular genetic diversity in these human samples can be attributed to “racial” differentiation. The median δ values for pairwise comparisons between groups fell between .15 and .20, permitting identification of highly informative RFLP loci for MALD disease association studies.     

Evaluation of counting error due to colony masking in bioaerosol sampling.

Colony counting error due to indistinguishable colony overlap (i.e., masking) was evaluated theoretically and experimentally. A theoretical model to predict colony masking was used to determine colony counting efficiency by Monte Carlo computer simulation of microorganism collection and development into CFU. The computer simulation was verified experimentally by collecting aerosolized Bacillus subtilis spores and examining micro- and macroscopic colonies. Colony counting efficiency decreased (i) with increasing density of collected culturable microorganisms, (ii) with increasing colony size, and (iii) with decreasing ability of an observation system to distinguish adjacent colonies as separate units. Counting efficiency for 2-mm colonies, at optimal resolution, decreased from 98 to 85% when colony density increased from 1 to 10 microorganisms cm-2, in contrast to an efficiency decrease from 90 to 45% for 5-mm colonies. No statistically significant difference (alpha = 0.05) between experimental and theoretical results was found when colony shape was used to estimate the number of individual colonies in a CFU. Experimental colony counts were 1.2 times simulation estimates when colony shape was not considered, because of nonuniformity of actual colony size and the better discrimination ability of the human eye relative to the model. Colony surface densities associated with high counting accuracy were compared with recommended upper plate count limits and found to depend on colony size and an observation system's ability to identify overlapped colonies. Correction factors were developed to estimate the actual number of collected microorganisms from observed colony counts.(ABSTRACT TRUNCATED AT 250 WORDS)     

A novel gene tag for identifying microorganisms released into the environment.

A novel method using a moc (mannityl opine catabolism) region from the Agrobacterium tumefaciens Ti plasmid pTi15955 was developed as a tag to identify genetically modified microorganisms released into the environment. Pseudomonas fluorescens 1855.344, a plant-growth-promoting rhizosphere bacterium, was chosen as the organism in which to develop and test the system. moc genes carried by pYDH208, a cosmid clone containing a 20-kb segment of the octopine-mannityl opine-type Ti plasmid, conferred on P. fluorescens strains the capacity to utilize mannopine and agropine (AGR) as a sole source of carbon and energy. Modified P. fluorescens strains containing moc or moc::nptII inserted into a chromosomal site were constructed by marker exchange. One such modified strain, PF5MT12, utilized AGR as a sole carbon source and contained detectable levels of mannopine cyclase, an easily assayable enzyme encoded by the moc region. Catabolism of AGR could be used to recover selectively the marked strain from mixed populations containing a large excess of closely related bacteria. Nucleic acid-based detection strategies were developed on the basis of the unique fusion region between Agrobacterium DNA and Pseudomonas DNA in strain PF5MT12. The specificity and sensitivity of detection of PF5MT12 were enhanced by amplifying the fused DNA region by using PCR. The target fragment could be detected at levels of sensitivity comparable to those of other described PCR-based gene tags, even in the presence of high levels of Agrobacterium, Pseudomonas, or Escherichia coli DNA. This gene tag strategy gives a method for direct selection and enumeration of the marked strain from mixtures containing a large excess of closely related bacteria and a sensitive and highly specific system for detection by PCR amplification of the target fragment even in the presence of large amounts of DNA from related or unrelated organisms.     

Comparison of combinations of diluents and media for enumerating Zygosaccharomyces rouxii in intermediate water activity foods

Combinations of five diluents (0.1% peptone, 40 and 50% glucose, and 18 and 26% glycerol) and three enumeration media (tryptone glucose yeast extract, dichloran 18% glycerol and malt extract yeast extract 50% glucose (MY50G) agars) were evaluated for recovering a xerotolerant yeast, Zygosaccharomyces rouxii , from foods with intermediate water activity ( a _w). Combinations of 40% ( a _w, 0.936) or 50% ( a _w 0.898) glucose diluent and MY50G agar ( a _w 0.890) were superior in recovering highest populations. The type of solute in the diluent, as well as a reduced a _w, influences efficiency of recovering viable cells.     

Effect of biocatalyst activity changes in continuous reactions in the gas phase

Summary In the gas phase bioreactions, continuous production rate depends on the biocatalyst activity and complete dehydration causes the biocatalyst to lose most of its activity. To overcome these difficulties, a theoretical method is suggested along with the new design of biocatalyst. This will be applicable and helpful for the optimization of the gas phase continuous bioreaction.Nomenclature C_A ethanol concentration [mol/mL] - C_P acetaldehyde concentration [mol/mL] - X_P acetaldehyde composition     

Disposition kinetics of ML-1035 sulfoxide enantiomers and the prochiral sulfide in rats

ML-1035, 4-amino-5-chloro-2-[2-(methylsulfinyl)ethoxy]-N-[2-(diethylamino)ethyl]benzamide, is a sulfoxide compound and a racemic gastroprokinetic agent with a chiral center at the sulfur atom. We have investigated the disposition kinetics of (R)-ML-1035 sulfoxide (R) and (S)-ML-1035 sulfoxide (S) after the single enantiomers and the racemic mixture were administered to rats in separate experiments. There was no noticeable chiral inversion after either enantiomer dose. Both enantiomers were rapidly absorbed. After dosing with enantiomers or with the racemate, the resulting plasma concentration-time curve of R was closely parallel to that of S in both intravenous and oral experiments, suggesting that the two enantiomers have approximately the same disposition kinetics. After intravenous enantiomer doses, only S underwent conversion to sulfide, suggesting that sulfidation in the liver is enantioselective. However, the enantioselective sulfidation after intravenous dosing did not introduce a difference in the global plasma disposition profiles between R and S, since the reduction reaction is a minor metabolic process. Other metabolic reactions such as sulfonation and mono-N-desethylations were not enantioselective. After oral administration, conversion to sulfide was observed for both enantioners, implicating the existence of a nonhepatic pathway in sulfidation. Administration of a prochiral sulfide dose was associated with an enantioselective sulfoxidation, in which the R/S concentration ratios increased as a function of time. In addition, enantiomeric interaction causing changes in pharmacokinetic parameters was observed after the oral racemate dose, while the interaction is negligible after an intravenous racemate dose, indicating a route dependency in enantiomeric interaction. © 1993 Wiley-Liss, Inc.