Cometabolic transformation ofo-xylene in a biofilm system under nitrate reducing conditions

The purpose of this work was to investigate the anaerobic transformation ofo-xylene in a laboratory biofilm system with nitrate as an electron acceptor.o-Xylene was degraded cometabolically with toluene as primary carbon source. A mass balance showed thato-xylene was not mineralized but transformed.o-Methyl-benzalcohol ando-methyl-benzaldehyde were identified as intermediates ofo-xylene transformation which resulted in the formation ofo-methyl-benzoic acid as an end product. A cross inhibition phenomenon was observed between toluene ando-xylene. The presence of toluene was necessary for stimulation ofo-xylene transformation, but above a toluene concentration of 1–3 mg/L theo-xylene removal rate dramatically decreased. In returno-xylene inhibited the toluene degradation at concentrations above 2–3 mg/L.     

Biofilm formation on brass coupons exposed to a cooling system of an oil refinery

Brass coupons (70% Cu 30% Zn) were exposed to a cooling freshwater system of an oil refinery, in order to investigate susceptibility of the metal to biofilm formation. The coupons were fixed on bypasses at points which allowed the circulation of makeup, cooling and return water. The number of aerobic, anaerobic and sulfate-reducing bacteria was determined in both the planktonic and the sessile phases. Maximum bacterial concentrations were detected in the cooling water, corresponding to 2.1 ± 0.1 × 10⁶ CFU ml⁻¹ (planktonic phase) and 1.3 ± 0.2 × 10⁵ CFU cm⁻² (sessile phase) for aerobic bacteria and to 3.2 ± 0.3 × 10⁵ cells ml⁻¹ (planktonic phase) and 6.2 ± 0.7 × 10⁵ cells cm⁻² (sessile phase) for anaerobic bacteria. Sulfate-reducing bacteria (SRB) were observed only in the planktonic phase, being found in greater numbers in the return water. Scanning electron microscopy (SEM) analysis indicated that biofilm formation occurred at the three monitored sites and showed a diversity in cell morphology. Nonetheless, no evidence of corrosion was observed on the brass coupons during the experimental period. Received 22 May 1997/ Accepted in revised form 19 September 1997     

Metabolic changes associated with biofilm formation in an undisturbed Mediterranean stream

Respiratory activity (ETS), ectoenzymatic activity (-glucosidase and -xylosidase) and photosynthetic ¹⁴C-bicarbonate incorporation in the biofilm were measured in a shaded stream during a colonization sequence (43 days) on artificial substrates (unglazed clay tiles) and compared with older (aged) tiles. In the first five days bacterial densities and ectoenzyme activities showed a sharp increase. After two weeks, algal density, chlorophyll and productivity increased moderately. Chlorophyll did not reach similar values to those of the aged biofilms until the last day of colonization. Photosynthetic activity seemed to be relevant to the heterotrophs metabolism during substrate colonization, as could be deduced from the significant correlation between -glucosidase and ¹⁴C-bicarbonate incorporation, algal cell densities and chlorophyll. Respiratory activity (ETS) decreased in the older biofilms, accordingly to their higher algal and bacterial density. Younger biofilms (up to 8 days old) showed higher ETS activity per cell, indicating a fast response of microorganisms to substrate availability.     

Initial development of conduction pattern of spontaneous action potential in early embryonic precontractile chick heart

The conduction of spontaneous action potentials in the 7-10 somite embryonic developing chick hearts was monitored optically using a potential-sensitive merocyanine-rhodanine dye. Spontaneous optical action signals from 5 to 12 different regions of the primitive heart were recorded simultaneously. Short delays were observed among firing times of the absorption signals which were nearly synchronized among the different regions. From these delays, we estimated the conduction velocity of the spontaneous excitatory waves. Usually, in the 7-somite to the beginning of the 9-somite stage, (i) excitatory waves conducted radially over one side of the prebeating heart, at a uniform rate; (ii) the "radially" spreading electrical wave slowed considerably within the primordial fusion line at the midline of the heart; and (iii) this delay disappeared in the later period of the 9-somite stage to the 10-somite stage. These observations suggest that electrical coupling among the cells within the primordial fusion line is poor during the 7 to 9-somite stage, and that the coupling is strengthened by the late 9th or 10th somite stage.     

Interobserver reliability of methods for paleopathological diagnosis of dental caries

There is disagreement as to whether clinical methods of caries diagnosis will produce reliable results in skeletal material, and studies vary greatly in the extent to which such methods are employed. The purpose of this study is, therefore, to evaluate the interobserver reliability of visual, tactile, and radiographic methods of scoring dental caries in ancient populations. Thirty-three individuals from a Mogollon skeletal sample were scored on three occasions by pairs of examiners. The first exam employed visual criteria alone. In the second exam, visual methods were supplemented with the dental explorer. For the third exam, mesial and distal surfaces were scored from “intraoral” radiographs. Examiners worked independently, but did calibrate on material from clinical populations prior to the second and third exams. Exams were conducted on a “blind” basis, and analysis was delayed until all exams were completed. Caries scores were expressed as a percentage of total surfaces present per individual. Repeat-measures ANOVA and intraclass correlation coefficients (ICC) were used to estimate interobserver reliabilities. For visual scores, ICC = 0.97, and there is no significant difference between examiners (P = 0.897). For visual plus explorer scores, ICC drops to 0.90, and there is a significant difference between examiners (P = 0.003). For the radiographs, ICC = 0.86, and there is no significant difference between observers (P = 0.117). These results suggest that clinical methods are less reliable in skeletal populations. Probable sources of error include postmortem dehydration of carious dentin, confusing radiolucencies engendered by worn or fractured enamel, and inadequate radiologic standards for root caries. These problems can be avoided through reliance on visual criteria.     

Effect of operating variables on biofilm formation and performance of an anaerobic fluidized-bed bioreactor

The effect of various operating variables such as initial inoculum circulation, dilution rate, chemical oxygen demand (COD) loading rate, and quantity and quality of inoculum on the process of film formation on sand surface and reactor performance were studied using synthetic glucose based wastewater. It was found that the film formation process is favored by a high dilution rate, a large quantity of inoculum, and an inoculum having high methane producing capacity. Experimental observations indicate that the biofilm formation process is initiated by methanogenic bacteria.     

Dental microwear in live, wild-trapped Alouatta palliata from Costa Rica

One problem with dental microwear analyses of museum material is that investigators can never be sure of the diets of the animals in question. An obvious solution to this problem is to work with live animals. Recent work with laboratory primates has shown that high resolution dental impressions can be obtained from live animals. The purpose of this study was to use similar methods to begin to document rates and patterns of dental microwear for primates in the wild. Thirty-three Alouatta palliata were captured during the wet season at Hacienda La Pacifica near Canas, Costa Rica. Dental impressions were taken and epoxy casts of the teeth were prepared using the methods of Teaford and Oyen (1989a). Scanning electron micrographs were taken of the left mandibular second molars at magnifications of 200x and 500x. Lower magnification images were used to calculate rates of wear, and higher magnification images were used to measure the size and shape of microwear features. Results indicate that, while basic patterns of dental microwear are similar in museum samples and samples of live, wild-trapped animals of the same species, ecological differences between collection locales may lead to significant intraspecific differences in dental microwear. More importantly, rates of microwear provide the first direct evidence of differences in molar use between monkeys and humans.     

Enamel structure and microwear: an experimental study of the response of enamel to shearing force.

The anisotropic fracturing and differential wear properties of enamel microstructure represent factors that can obscure the predictive relationship between dental microwear and diet. To assess the impact of enamel structure on microwear, this in vitro experimental study examines the relative contributions to wear of three factors: 1) species differences in microstructure, 2) direction of shearing force relative to enamel prisms and crystallites, and 3) size of abrasive particles. Teeth of Lemur, Ovis, Homo, and Crocodylus, representing, respectively, the structural categories of prismatic patterns 1, 2, and 3 and nonprismatic enamel, were abraded by shearing forces (forces having a component directed parallel to abraded surfaces) and examined by scanning electron microscopy. Striation width increased with particle size for nonprismatic, but not for prismatic, specimens. Direction of shear relative to prism and crystallite orientation had a significant influence on striation width in only some prismatic enamels. The different responses of prismatic and nonprismatic enamels to abrasion reflect the influence of structure, but at the level of organization of crystallites rather than prisms per se. Such interactions explain in part the inability of striation width to discriminate among animals with different dietary habits. Heteroscedasticity and deviations from normality also may confound parametric analyses of microwear variables. Variation in crystallite orientation in prismatic enamels may contribute to optimal dental function through the property of differential wear in functionally distinct regions of teeth.     

Immune modulation of connective tissue functions: studies on the production of collagen synthesis inhibitory factor by populations of human peripheral blood mononuclear cells

It has been shown previously that a soluble factor(s) from human peripheral blood mononuclear cells was capable of specifically suppressing collagen synthesis by normal human dermal fibroblasts (S. A. Jimenez, W. McArthur and J. Rosenbloom, J. Exp. Med.150, 1421, 1979). In this communication, the cell sources and the conditions for synthesis of this collagen synthesis inhibitory factor (CSIF) are identified. CSIF production by mononuclear cells was directly related to the number of cells in culture and was significantly enhanced by a variety of mitogens and by antigens. Homologous serum or bovine serum albumin was required for CSIF production and maximal levels were reached 48 hr after stimulation. Thymus-derived lymphocytes appeared to be the main cells responsible for CSIF synthesis but B lymphocytes also produced the factor in response to proper B-cell mitogens. Preparations of plastic-adherent mononuclear cells were also found to produce increased CSIF but it was not possible to exclude completely the presence of T lymphocytes in these preparations and therefore, the cell source of CSIF in these preparations was not clearly established. Through the use of metabolic inhibitors it was shown that CSIF production required de novo protein synthesis but not cell division. Indo-methacin had no effect on either the production of CSIF or on CSIF-mediated inhibition of collagen synthesis. The results indicate that CSIF has the classic characteristics of a lymphokine and suggest a mechanism by which the immune response could modulate connective tissue function.     

Mathematical model for the fluidized bed biofilm reactor

A mathematical model is proposed for the fluidized bed biofilm reactor (FBBR). For individual biofilm-covered particles (bioparticles) within the reactor, an analysis of intrabiofilm mass transfer and simultaneous intrinsic zero order reaction yields an effectiveness factor expression which is a function of the modified, zero order Thiele modulus, Φ_0,m. This expression is linked to a one-dimensional reactor flow model and a fluidization model to yield an overall reactor model describing convective transport and simultaneous biochemical conversion of substrate within a FBBR. For Φ_0,m<1.15, FBBR is mass transfer limited and 0.45 order kinetics are observed. For Φ_0,m<1.15, mass transfer limitations are insignificant and intrinsic zero order kinetics are observed. A sensitivity analysis using the proposed mathematical model indicates that biofilm thickness and media size are the two most important operating parameters. These two parameters can be optimized simultaneously for a specific application. The proposed model provides a rational approach for FBBR design.