Explaining the temperature dependence of spirilloxanthin's S* signal by an inhomogeneous ground state model.

We investigate the nature of the S* excited state in carotenoids by performing a series of pump-probe experiments with sub-20 fs time resolution on spirilloxanthin in a polymethyl-methacrylate matrix varying the sample temperature. Following photoexcitation, we observe sub-200 fs internal conversion of the bright S2 state into the lower-lying S1 and S* states, which in turn relax to the ground state on a picosecond time scale. Upon cooling down the sample to 77 K, we observe a systematic decrease of the S*/S1 ratio. This result can be explained by assuming two thermally populated ground state isomers. The higher lying one generates the S* state, which can then be effectively frozen out by cooling. These findings are supported by quantum chemical modeling and provide strong evidence for the existence and importance of ground state isomers in the photophysics of carotenoids.

Speciation and distribution of arsenic and localization of nutrients in rice grains.

Arsenic (As) contamination of rice grains and the generally low concentration of micronutrients in rice have been recognized as a major concern for human health. Here, we investigated the speciation and localization of As and the distribution of (micro)nutrients in rice grains because these are key factors controlling bioavailability of nutrients and contaminants. Bulk total and speciation analyses using high-pressure liquid chromatography (HPLC)-inductively coupled plasma mass spectrometry (ICP-MS) and X-ray absorption near-edge spectroscopy (XANES) was complemented by spatially resolved microspectroscopic techniques (micro-XANES, micro-X-ray fluorescence (micro-XRF) and particle induced X-ray emission (PIXE)) to investigate both speciation and distribution of As and localization of nutrients in situ. The distribution of As and micronutrients varied between the various parts of the grains (husk, bran and endosperm) and was characterized by element-specific distribution patterns. The speciation of As in bran and endosperm was dominated by As(III)-thiol complexes. The results indicate that the translocation from the maternal to filial tissues may be a bottleneck for As accumulation in the grain. Strong similarities between the distribution of iron (Fe), manganese (Mn) and phosphorus (P) and between zinc (Zn) and sulphur (S) may be indicative of complexation mechanisms in rice grains.

High percentage inorganic arsenic content of mining impacted and nonimpacted Chinese rice.

Two approaches were undertaken to characterize the arsenic (As) content of Chinese rice. First, a national market basket survey (n = 240) was conducted in provincial capitals, sourcing grain from China's premier rice production areas. Second, to reflect rural diets, paddy rice (n = 195) directly from farmers fields were collected from three regions in Hunan, a key rice producing province located in southern China. Two of the sites were within mining and smeltery districts, and the third was devoid of large-scale metal processing industries. Arsenic levels were determined in all the samples while a subset (n = 33) were characterized for As species, using a new simple and rapid extraction method suitable for use with Hamilton PRP-X100 anion exchange columns and HPLC-ICP-MS. The vast majority (85%) of the market rice grains possessed total As levels < 150 ng g(-1). The rice collected from mine-impacted regions, however, were found to be highly enriched in As, reaching concentrations of up to 624 ng g(-1). Inorganic As (As(i)) was the predominant species detected in all of the speciated grain, with As(i) levels in some samples exceeding 300 ng g(-1). The As(i) concentration in polished and unpolished Chinese rice was successfully predicted from total As levels. The mean baseline concentrations for As(i) in Chinese market rice based on this survey were estimated to be 96 ng g(-1) while levels in mine-impacted areas were higher with ca. 50% of the rice in one region predicted to fail the national standard.

Histologic detection of cardiac musculature, soy flour, and partially defatted tissue in ground beef: interlaboratory study.

A collaborative study was designed and conducted to evaluate the accuracy of a procedure for the histologic detection of cardiac muscle, soy flour, and partially defatted tissue that may occur as adulterants in ground beef. Ground beef samples were prepared containing 0, 3, 5, 10, and 15% of each of the 3 adulterants. Five samples of each composition at each of the 5 dilutions, for a total of 75 unknown samples, were analyzed at each of 5 participating laboratories. The study revealed that this technique is reliable for the detection of these adulterants in ground beef.

Outer membrane permeability in Pseudomonas aeruginosa: comparison of a wild-type with an antibiotic-supersusceptible mutant.

The Pseudomonas aeruginosa mutant Z61 has been shown to be highly supersusceptible to a wide range of antibiotics, including beta-lactams, aminoglycosides, rifampin, tetracycline, and chloramphenicol (W. Zimmerman, Int. J. Clin. Pharmacol. Biopharm. 17:131-134, 1979). Spontaneous revertants were isolated, using gentamicin or carbenicillin as selective agents, and shown to have two patterns of susceptibility to a group of 12 antibiotics. Partial revertants had 2- to 10-fold greater resistance to these antibiotics than mutant Z61, whereas full revertants had antibiotic susceptibilities indistinguishable from those of the wild-type strain K799, from which mutant Z61 had been derived. Uptake of a chromogenic beta-lactam nitrocefin was studied in both uninduced and induced cells of all strains by measuring the steady-state rate of nitrocefin hydrolysis by the inducible, periplasmic beta-lactamase in both whole and broken cells. This demonstrated that outer membrane permeability decreased as antibiotic resistance increased in the series mutant Z61, partial revertants, wild type, and full revertants. The data were consistent with the idea of low outer membrane permeability being caused by a low proportion of open functional porins in the outer membrane as the reason for the high natural antibiotic resistance of wild-type P, aeruginosa strains. In addition, it was observed that levels of benzylpenicillin below the minimal inhibitory concentration for mutant Z61 failed to induce beta-lactamase production. The possibility that this was related to the observed increase in outer membrane permeability is discussed. Preliminary evidence is presented that the pore-forming outer membrane porin protein F is not altered in mutant Z61.

Evaluation of iron dextran and mucin for enhancement of the virulence of Yersinia enterocolitica serotype O:3 in mice.

The pathogenic role of Yersinia enterocolitica serotypes O:3, O:8, and O:9 in human infections is well documented. Whereas the virulence of the O:8 strains can be readily demonstrated in mice by 50% lethal dose determinations, the O:3 and O:9 strains have no lethal effect on mice by any route of inoculation. A mouse virulence test for the O:3 and O:9 strains is described. Y. enterocolitica strains were first tested for the presence of virulence-associated plasmid characteristics by auto-agglutination and gel electrophoresis procedures before mouse virulence determinations. The 50% lethal dose of the O:3 strains injected intraperitoneally with 2.5% mucin was about 10(7) colony-forming units. However, histological examinations showed that mucin allowed the growth of Y enterocolitica on the surface of the livers and spleens of the mice without internal lesions. The 50% lethal dose of the same O:3 strains injected intraperitoneally with 1 ml of 10% iron dextran in saline was about 10(5) to 10(6) colony-forming units, and the nonlethal infective dose with typical lesion development was 20 to 200 colony-forming units. The infected mice developed symptoms and extensive liver and spleen lesions which differed from those in mice infected intraperitoneally with the virulent O:8 strains. These results showed that the virulence of the O:3 Y. enterocolitica strains can be measured by intraperitoneal injection with iron dextran. This procedure was used to test the virulence of food isolates, plasmidless strains, and the effect of growth temperatures.

Pseudomonas aeruginosa outer membrane: peptidoglycan-associated proteins.

The Pseudomonas aeruginosa outer membrane was isolated with attached peptidoglycan and fractionated with Triton X-100, ethylenediaminetetraacetate, and lysozyme. The data suggest that major outer membrane proteins F, H2, and I are noncovalently associated with the peptidoglycan.

Outer membrane of Pseudomonas aeruginosa: heat- 2-mercaptoethanol-modifiable proteins.

A number of polyacrylamide gel systems and solubilization procedures were studied to define the number and nature of "major" polypeptide bands in the outer membrane of Pseudomonas aeruginosa. It was shown that five of the eight major outer membrane proteins were "heat modifiable" in that their mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis was determined by the solubilization temperature. Four of these heat-modifiable proteins had characteristics similar to protein II of the Escherichia coli outer membrane. Addition of lipopolysaccharide subsequent to solubilization caused reversal of the heat modification. The other heat-modifiable protein, the porin protein F, was unusually stable to sodium dodecyl sulfate. Long periods of boiling in sodium dodecyl sulfate were required to cause conversion to the heat-modified form. This was demonstrated both with outer membrane-associated and purified lipopolysaccharide-depleted protein F. Furthermore, lipopolysaccharide treatment had no effect on the mobility of heat-modified protein F. Thus it is concluded that protein F represents a new class of heat-modifiable protein. It was further demonstrated that the electrophoretic mobility of protein F was modified by 2-mercaptoethanol and that the 2-mercaptoethanol and heat modification of mobility were independent of one another. The optimal conditions for the examination of the outer membrane proteins of P. aeruginosa by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis are discussed.