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PubMed2006

Rapid chromatic detection of bacteria by use of a new biomimetic polymer sensor.

We present a new platform for visual and spectroscopic detection of bacteria. The detection scheme is based on the interaction of membrane-active compounds secreted by bacteria with agar-embedded nanoparticles comprising phospholipids and the chromatic polymer polydiacetylene (PDA). We demonstrate that PDA undergoes dramatic visible blue-to-red transformations together with an intense fluorescence emission that are induced by molecules released by multiplying bacteria. The chromatic transitions are easily identified by the naked eye and can also be recorded by conventional high-throughput screening instruments. Furthermore, the color and fluorescence changes generally occur in shorter times than the visual appearance of bacterial colonies on the agar. The chromatic technology is generic and simple, does not require identification a priori of specific bacterial recognition elements, and can be applied for detection of both gram-negative and gram-positive bacteria. We demonstrate applications of the new platform for reporting on bacterial contaminations in foods and for screening for bacterial antibiotic resistance.

Agar↗
PubMed1993

Chromate Reduction by Resting Cells of Agrobacterium radiobacter EPS-916.

Resting cells of Agrobacterium radiobacter EPS-916 grown on glucose, fructose, maltose, lactose, mannitol, or glycerol reduced 0.5 mM chromate. However, resting cells of strain EPS-916 grown on glutamate or succinate did not reduce chromate. The ability of washed cells to reduce chromate was correlated with their redox potential.

Journal Article↗
PubMed1977

Occurrence and nature of chromatic adaptation in cyanobacteria.

Forty-four axenic strains of cyanobacteria that synthesize phycoerythrin were screened to ascertain the effect of light quality on pigment synthesis. Cellular pigment compositions were determined after photoautotrophic growth with low light fluxes (7.0 X 10(2) ergs/cm2 per s) of green, red, and white light, and in the case of facultative heterotrophs, after dark growth at the expense of sugars. Twelve strains did not adapt chromatically: the cells contained fixed proportions of phycoerythrin, phycocyanin, and allophycocyanin under the growth conditions used. In the remaining strains, the cellular ratio of phycoerythrin to phycocyanin was much higher after growth in green than in red light. Quantitative data on the cellular pigment contents, supplemented by measurements of the differential rates of pigment synthesis on representative strains, show that chromatic adaptation may involve a light-induced modulation either of phycoerythrin synthesis alone (7 strains) or of both phycoerythrin and phycocyanin synthesis (25 strains). Facultative hetrotrophs able to adapt chromatically have a phycobiliprotein composition after dark growth which closely resembles that after growth in red light. Light quality does not affect the differential rate of chlorophyll synthesis. The physiological and taxonomic implications of these findings are discussed.

Adaptation, Physiological↗
PubMed1983

Mutations affecting chromatic adaptation in the cyanobacterium Fremyella diplosiphon.

The chromatically adapting cyanobacterium, Fremyella diplosiphon, when grown in cool white fluorescent light, contains phycoerythrin as its predominant phycobiliprotein. When grown on agar plates with cool white illumination, mutant colonies deficient or devoid of phycoerythrin can be visibly distinguished from the wild type. A total of 25 anomalously pigmented strains were isolated and examined for their ability to chromatically adapt. Based on absorption spectra of cell extracts and on fluorescence emission spectra of intact filaments, we assigned each mutant to one of three classes. In green mutants (16 strains), the photoinduction of phycoerythrin synthesis by green light was lost or impaired, whereas the photorepression of phycocyanin synthesis by green light still functioned as in the wild type. In blue mutants (eight strains), both the ability to photoinduce phycoerythrin synthesis and the ability to photorepress phycocyanin synthesis were lost or impaired. Filaments of blue mutants exhibited a high fluorescence emission at 660 nm. A black mutant (one strain) exhibited partial induction of phycoerythrin and partial repression of phycocyanin in both red and cool white light. From the data, we suggest that in information transduction for chromatic adaptation, early events are common to both phycoerythrin and phycocyanin regulation and that blue mutants possess lesions in these early events. The lesions in green mutants occur in a subsequent branch of the information transduction pathway which is specific for phycoerythrin photoinduction.

Adaptation, Biological↗
PubMed1990

Membrane-associated chromate reductase activity from Enterobacter cloacae.

Washed cells of Enterobacter cloacae HO1 reduced hexavalent chromium (chromate: CrO4(2-) anaerobically. Chromate reductase activity was preferentially associated with the membrane fraction of the cells. Right-side-out membrane vesicles prepared from E. cloacae cells showed high chromate reductase activities when ascorbate-reduced phenazine methosulfate was added as an electron donor.

Cell Membrane↗
PubMed1997

New classes of mutants in complementary chromatic adaptation provide evidence for a novel four-step phosphorelay system.

Complementary chromatic adaptation appears to be controlled by a complex regulatory system with similarity to four-step phosphorelays. Such pathways utilize two histidine and two aspartate residues for signal transduction. Previous studies of the signaling system controlling complementary chromatic adaptation have uncovered two elements of this pathway, a putative sensor, RcaE, and a response regulator, RcaC. In this work, we describe a second response regulator controlling complementary chromatic adaptation, RcaF, and identify putative DNA binding and histidine phosphoacceptor domains within RcaC. RcaF is a small response regulator with similarity to SpoOF of Bacillus subtilis; the latter functions in the four-step phosphorelay system controlling sporulation. We have also determined that within this phosphorelay pathway, RcaE precedes RcaF, and RcaC is probably downstream of RcaE and RcaF. This signal transduction pathway is novel because it appears to use at least five, instead of four, phosphoacceptor domains in the phosphorelay circuit.

Amino Acid Sequence↗
PubMed1997

Suppression of mutants aberrant in light intensity responses of complementary chromatic adaptation.

Complementary chromatic adaptation is a process in which cyanobacteria alter the pigment protein (phycocyanin and phycoerythrin) composition of their light-harvesting complexes, the phycobilisomes, to help optimize the absorbance of prevalent wavelengths of light in the environment. Several classes of mutants that display aberrant complementary chromatic adaptation have been isolated. One of the mutant classes, designated "blue" or FdB, accumulates high levels of the blue chromoprotein phycocyanin in low-intensity green light, a condition that normally suppresses phycocyanin synthesis. We demonstrate here that the synthesis of the phycocyanin protein and mRNA in the FdB mutants can be suppressed by increasing the intensity of green light. Hence, these mutants have a decreased sensitivity to green light with respect to suppression of phycocyanin synthesis. Although we were unable to complement the blue mutants, we did isolate genes that could suppress the mutant phenotype. These genes, which have been identified previously, encode a histidine kinase sensor and response regulator protein that play key roles in controlling complementary chromatic adaptation. These findings are discussed with respect to the mechanism by which light quality and quantity control the biosynthesis of the phycobilisome.

Adaptation, Physiological↗
PubMed1980

Chromium content of lungs of chromate workers with lung cancer.

The chromium content was measured in the lungs of chromate workers, obtained at necropsy in six patients and at surgery in two. The mean chromium content of peripheral lung tissue was 36.7 micrograms per gm wet weight (range 0.50 to 130.2 micrograms) and that of the large airways was 0.51 micrograms per gm wet weight (range 0.22 to 0.99 micrograms). These means values were high compared with those from control lungs of a non-chromate exposed lung cancer patients--respectively 0.21 micrograms per gm in lung tissue and 0.11 micrograms per gm in the large bronchi. The longer the exposure period, the higher was the chromium content in the lungs. The concentration of chromium in the upper lobes was significantly higher than that in the lower lobes, suggesting regional differences either in clearance from or deposition in the lung. Moreover, it was apparent that the metal remained in the lungs long after exposure to chromate had ceased

Aged↗
PubMed1994

Effects of a chromated-copper-arsenate wood preservative on the bacterial degradation of pentachlorophenol.

The effect of a chromated-copper-arsenate wood preservative on the degradation of pentachlorophenol by Flavobacterium sp. strain ATCC 53874 was examined in liquid culture. Both a commercially available and a laboratory-prepared formulation were tested. Each increased the lag time required for measurable pentachlorophenol degradation and the time required for complete degradation to nondetectable levels. This response was noted at all pentachlorophenol concentrations examined (10, 25, 50, 75, and 100 micrograms.mL-1). The commercial formulation of chromated-copper-arsenate had the more significant impact on pentachlorophenol degradation. Inhibitory effects were evident at chromated-copper-arsenate component metal concentrations 0.1-0.5 mg.L-1. These levels are thousands of times below those used commercially.

Arsenates↗
PubMed1995

Alterations in chromatic contour perception in de novo parkinsonian patients.

Recently abnormalities of chromatic visual perception were reported in treated patients with Parkinson's disease (PD). We studied 28 previously untreated Parkinsonian patients and 28 age- and sex-matched controls using a computer-aided method to determine the chromatic fusion time (CFT). CFT indicates the acuity of the perception of monochromatic contours. Patients with PD have a shortened CFT especially for the light-blue and dark-green stimuli. The chromatic perception disorder is correlated with the severity of PD. It can be concluded from our data that the dysfunction of colour perception is related to the pathophysiology of PD.

Adult↗
PubMed2004

Perceived surface color in binocularly viewed scenes with two light sources differing in chromaticity.

We examined the effect of perceived orientation on the perceived color of matte surfaces in rendered three-dimensional scenes illuminated by a blue diffuse light and a yellow punctate light. On each trial, observers first adjusted the color of a matte test patch, placed near the center of the scene, until it appeared achromatic, and then estimated its orientation by adjusting a monocular gradient probe. The orientation of the test patch was varied from trial to trial by the experimental program, effectively varying the chromaticity of the light mixture from the two light sources that would be absorbed and reemitted by a neutral test patch. We found that observers' achromatic settings varied with perceived orientation but that observers only partially discounted orientation in making achromatic settings. We developed an equivalent illuminant model for our task in which we assumed that observers discount orientation using possibly erroneous estimates of the chromaticities of the light sources and/or their spatial distribution. We found that the observers' failures could be explained by two factors: errors in estimating the direction to the punctate light source and errors in estimating the chromaticities of the two light sources. We discuss the pattern of errors in estimating these factors across observers.

Color Perception↗
PubMed2005

Chromatic and luminance contrast sensitivities in asymptomatic carriers from a large Brazilian pedigree of 11778 Leber hereditary optic neuropathy.

PURPOSE: To determine whether asymptomatic 11778 LHON carriers demonstrated impairments in (1) chromatic red/green (R/G) and blue/yellow (B/Y) contrast sensitivity functions (CSF) and in (2) luminance contrast sensitivity functions in the spatial CSF (SCSF) and temporal CSF (TCSF) domains. METHODS: Twenty-five carriers (8 male, 17 female; 34.1 +/- 15.1 years of age) of homoplasmic 11778 LHON from the same well-described family and 30 age-matched controls (17 male, 13 female; 29.2 +/- 7.1 years of age) were tested in one eye, randomly selected. Of the 25 eyes tested, 18 had normal fundus, 5 had swelling and microangiopathy, and 2 had temporal pallor. The R/G and B/Y CSFs were obtained after equiluminance correction with bichromatic horizontal sinusoidal gratings at 0.3, 0.7, and 2 cycles per degree (cpd); the SCSFs were obtained with achromatic gratings at 0.3, 2, 6, and 12 cpd; and the TCSFs were obtained at 2, 10, 20, and 33 Hz with sinusoidal modulation of a 2.7 degrees field with a superimposed spatial Gabor function. RESULTS: Differences between carriers and controls were statistically significant for all spatial frequencies of chromatic and luminance SCSFs, but not for the TCSFs. R/G equiluminance settings of carriers differed from those of controls (P < 0.001), requiring higher luminance in the green; B/Y equiluminance settings were not statistically different in carriers and controls. Fundus findings did not correlate with CS results. CONCLUSIONS: Luminance and chromatic spatial CS losses that affected all tested spatial frequencies, are reported in LHON asymptomatic carriers with the mtDNA 11778 mutation. No losses were found in the temporal CSF. An intriguing finding is that the blue system is substantially spared in this LHON family. These represent subclinical visual impairments in otherwise asymptomatic LHON carriers.

Adolescent↗
PubMed1979

Chromatic border distinctness: not an index of hue or saturation differences.

Some investigators have suggested that the distinctness of chromatic borders (i.e., borders visible in photic arrays of uniform luminance) can be used as an index of hue and saturation differences between lights. However, recent evidence indicates that only two types of cones in the trichromatic eye contribute to chromatic border perception. A series of experiments are reported that were designed to discriminate between these alternatives, utilizing mainly the short-wavelength visible spectrum. The results support the notion that only R and G cones in the trichromatic eye mediate the perception of chromatic borders; thus the distinctness of such borders alone cannot be used as an index of either hue or saturation differences, because both of these aspects of color involve contributions from B cones.

Color Perception↗
PubMed1979

Luminace, not brightness, determines temporal brightness enhancement with chromatic stimuli.

Brightness-duration relations for chromatic stimuli were studied using three pulse-to-background luminace relations: chromatic equal-luminance pulses (3.2 cd/m2) were presented as increments of 0.3 or 1.0 log units above a lower luminance achromatic background, or were presented in hue substitution, equated in luminance to the achromatic background, so that no spatio-temporal luminance transients occurred during stimulus presentation. Incremental pulses produced temporal brightness enhancement (the Broca-Sulzer phenomenon), but hue substitution pulses did not. Temporal brightness enhancement thus depends upon the occurrence of luminance transients and cannot be produced by pulsed-to-background brightness differences associated solely with chromaticity differences.

Color Perception↗
PubMed1981

Estimates for the temporal response characteristics of chromatic pathways.

When equiluminous red and green fields are temporally alternated, it is generally accepted that the hue of the field fuses to yellow at a slower flicker rate than the critical flicker frequency (cff). However, when sufficient precautions are taken to avoid optically created achromatic artifacts and the illumination of the test field is kept fairly low (70 trolands), the modulation threshold for color fusion and that for flicker fusion are equivalent. The purely chromatic, artifact-free stimulus shows a much lower cff than has been reported in the literature under comparable conditions. It seems likely that many studies of the chromatic pathways have overestimated the ability of these pathways to follow rapid temporal alternation, presumably because the more sensitive achromatic pathways were detecting achromatic artifacts. A simple means for detecting achromatic artifacts in a temporal alternation will be demonstrated by the finding that an equiluminous surrounding field enhances modulation sensitivity only for achromatic flicker and not for chromatic flicker.

Color Perception↗
PubMed1983

Functional relationship between chromatic induction and luminance of the inducing stimulus.

We determined the functional relationship between chromatic induction and luminance of the inducing stimulus for different spatial conditions and assessed whether the effects of luminance and spatial variables could be explained in terms of the total effective energy in the inducing field. The result showed that the relationship between chromatic induction and luminance of the inducing stimulus could be mathematically expressed by an exponential function of the luminance ratio between the test and inducing stimuli and that the coefficient of the exponent was independent of spatial variables, i.e., area and separation. This led to the conclusion that a luminance ratio between two fields, rather than a quantum energy of the inducing field, was a relevant determinant of the effect of luminance of the inducing stimulus on chromatic induction.

Adult↗
PubMed1993

Achromatic and chromatic sensation as a function of color temperature and retinal illuminance.

Changes in color appearance with retinal illuminance were studied by scaling the achromatic, yellow, and blue sensation components for test lights with color temperatures from 3041 to 8650 K at 4.10, 2.18, and 0.33 log Td. At 4.10 log Td two observers showed similar pure whites (4823 and 5258 K) and narrow transition zones (1502 and 969 K) from yellow to blue chromatic response categories. The relative amounts of yellow, blue, and white varied with color temperature in a similar manner for both observers. One observer maintained similar absolute whites and transition zones for all illuminances. For the second observer the transition zone broadened and shifted to higher color temperatures as illuminance decreased. At color temperatures both above and below the transition zone chromatic saturation was greatest at the intermediate illuminance. The loss of saturation at 0.33 and 4.10 log Td is consistent with the observation that as the illuminance of a spectral color is raised above threshold, saturation increases to a maximum and then falls. Our findings reinforce the notion that at relatively low illuminances chromatic responses increase with increasing illuminance more rapidly than achromatic responses and that the opposite is true at high illuminances.

Adult↗
PubMed1993

Chromatic adaptation alters spectral sensitivity at high temporal frequencies.

To evaluate the effects of chromatic adaptation on spectral sensitivity at temporal frequencies within the region of high-frequency linearity, critical flicker frequency was measured as a function of red-green luminance ratio for counterphase flicker of 649- and 555-nm light. For eight observers, the relative weight of the contribution of the long-wavelength-sensitive cones to flicker detection was smaller on long-wavelength adapting fields than on middle-wavelength adapting fields even though long-wavelength-sensitive-cone modulations were high. These data indicate that chromatic adaptation can confound the interpretation of flicker-sensitivity data that are gathered with long-wavelength test lights or with equiluminant heterochromatic flicker and that there can be considerable interobserver variability in the effects of chromatic adaptation.

Adaptation, Ocular↗