Zeta Potential of Selected Bacteria in Drinking Water When Dead, Starved, or Exposed to Minimal and Rich Culture Media

The zeta potentials of E. coli, GFP (green fluorescence protein)-labeled E. coli, Salmonella Newport, and Pseudomonas sp. in different states (nutrient-starved and dead) and grown in rich and minimal media were measured. Capillary electrophoresis experiments were conducted to measure the zeta potential of the different cells suspended in a drinking water sample. Salmonella Newport strain showed a lower zeta potential compared to E. coli, GFP-labeled E. coli, and Pseudomonas sp. Starved E. coli cells had a lower zeta potential compared to E. coli cells grown under rich media conditions. Salmonella Newport cells grown in minimal media also had a lower zeta potential compared to rich, starved, and dead cells. The different bacterial cell types exhibited differences in size as well. These results suggest that when bacterial cells are present in drinking water they can exhibit significant heterogeneity in the size and zeta potential, depending on their physiological state.     

Genistein abolishes nucleoside uptake by cardiac fibroblasts

Genistein, a soy isoflavone, is reported to exert significant beneficial action in several human disorders, which has generated immense interest in the mechanisms underlying its effects on diverse cellular processes. It has anti-proliferative action on many cell types, an effect generally attributed to tyrosine kinase inhibition. In this study, genistein was found to cause total inhibition of [³H]-thymidine incorporation into DNA and a modest reduction in [³H]-proline incorporation into protein in primary cultures of cardiac fibroblasts. The decrease in [³H]-thymidine incorporation was not associated with a decrease in cell proliferation but correlated exactly with low intracellular levels of [³H]-thymidine. Genistein dramatically reduced [³H]-thymidine but not [³H]-proline uptake by these cells in which the equilibrative nucleoside transporter may be the major route of nucleoside uptake. The effect was irreversible and was demonstrable in pulmonary fibroblasts as well. The findings suggest that nucleoside uptake mechanisms may be a novel target of genistein action in cardiac fibroblasts and point to serious limitations in using genistein to assess the role of tyrosine kinase in cell proliferation by the standard technique of [³H]-thymidine incorporation.     

Stereospecific opiate receptors in the actions of thyrotropin releasing hormone and morphine on gastrointestinal transit

Studies in these laboratories have shown that morphine and thyrotropin releasing hormone (TRH) inhibit gastrointestinal transit in the mouse. Administration of morphine sulfate (5 mg/kg, s.c.) or TRH (10 microgram i.c.v.) to mice inhibited gastrointestinal transit as measured by the charcoal meal test. In order to determine whether the effects of TRH and morphine were mediated via stereospecific opiate receptors, the effects of two stereoisomers of an antagonist, (-) alpha -5,9-diethyl-2'-hydroxy-2-(3-furylmethyl)6,7-benzomorphan (MR2266), the active isomer and (+) alpha-5,9-diethyl-2'-hydroxy-2-(3-furylmethyl)6,7-benzomorphan (MR 2267), the inactive isomer, on morphine and TRH induced changes in gastrointestinal transit were determined. Morphine and THR induced inhibition of gastrointestinal transit was antagonized by MR 2266 (1 and 3 mg/kg, s.c.) but was unaffected by MR 2267. These studies provide evidence for the involvement of opiate receptors in the actions of morphine and TRH on gastrointestinal transit, and further suggest that the receptors are stereospecific in nature.     

Elucidation of the flavonoid catabolism pathway in Pseudomonas putida PML2 by comparative metabolic profiling.

Flavonoids are 15-carbon plant secondary metabolites exuded in the rhizosphere that hosts several flavonoid-degrading bacteria. We studied flavonoid catabolism in a plant growth-promoting rhizobacterial strain of Pseudomonas by using a combination of biochemical and genetic approaches. Transposants carrying mini-Tn5gfp insertions were screened for flavonoid auxotrophy, and these mutant strains were found to be unable to grow in the flavonols naringenin and quercetin, while their growth in glycerol was comparable to that of the parental strain. In order to understand flavonoid catabolism, culture supernatants, whole-cell fractions, cell lysate, and cell debris of the wild-type and mutant strains were analyzed. Intermediates that accumulated intracellularly and those secreted in the medium were identified by a combination of reversed-phase high-pressure liquid chromatography and electrospray ionization-mass spectrometry. Structures of four key intermediates were confirmed by one-dimensional nuclear magnetic resonance spectroscopy. Comparative metabolic profiling of the compounds in the wild-type and mutant strains allowed us to understand the degradation events and to identify six metabolic intermediates. The first step in the pathway involves 3,3'-didehydroxylation, followed by hydrolysis and cleavage of the C-ring, leading via subsequent oxidations to the formation of protocatechuate. This is the first report on quercetin dehydroxylation in aerobic conditions leading to naringenin accumulation.