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Effects of three heavy metals on the bacteria growth kinetics: a bivariate model for toxicological assessment

The effects of three heavy metals (Co, Ni and Cd) on the growth kinetics of five bacterial strains with different characteristics (Pseudomonas sp., Phaeobacter sp. strain 27-4, Listonella anguillarum, Carnobacterium piscicola and Leuconostoc mesenteroides subsp. lysis) were studied in a batch system. A bivariate model, function of time and dose, is proposed to describe simultaneously all the kinetic profiles obtained by incubating a microorganism at increasing concentrations of individual metals. This model combines the logistic equation for describing growth, with a modification of the cumulative Weibull’s function for describing the dose-dependent variations of growth parameters. The comprehensive model thus obtained—which minimizes the effects of the experimental error—was statistically significant in all the studied cases, and it raises doubts about toxicological evaluations that are based on a single growth parameter, especially if it is not obtained from a kinetic equation. In lactic acid bacteria cultures (C. piscicola and L. mesenteroides), Cd induced remarkable differences in yield and time course of characteristic metabolites. A global parameter is defined (ED50,τ: dose of toxic chemical that reduces the biomass of a culture by 50% compared to that produced by the control at the time corresponding to its semi maximum biomass) that allows comparing toxic effects on growth kinetics using a single value.Peer reviewe

Lean, unha soa escena

Murado, M. (1993). Lean, unha soa escena. Vértigo. Revista de cine. (8):42-43. http://hdl.handle.net/10251/42991.Importación Masiva4243

Mathematical modeling of area under the curve assessment criteria to quantify the antioxidant and pro-oxidant capacity: Coffee extracts as a case study

35 páginas, 5 figuras, 2 tablasThe development of a convenient mathematical application for testing the antioxidant and pro-oxidant capacity is essential in order to investigate potential sources of new agents and processes. In this regard, authors use the standardized values of the area under the curve of a kinetic profile of a dose-response agent, as a way to bypass the complex process of analyzing the kinetic variations of agents. In general, linear approaches are used, but such patterns frequently lead to unreliable results and misinterpretations, making it extremely difficult to compare the results from different assays. In this work, we have demonstrated the non-linearity of the dose-response area under the curve assessment criteria by means of simulations. A simple non-linear dose-response model was developed to describe the accurately response. As case study, experimental data of extracts of unroasted coffee beans from five different country-climate locations for the two most common coffee varieties (Robusta and Arabica) were obtained using the β-carotene and crocin bleaching in vitro assays. Their antioxidant capacity was analyzed in detail and compared with commercial standards. The results shows that the antioxidant capacity was greater than some of the commercial standards in terms of its maximum capacity, while when the analyses are based on rate parameters, the coffee extracts show between 6 to 40 times lower values than the standard antioxidants. In addition, to illustrate the advantages of using the standardized area units and the mathematical model developed, other more complex scenarios were recreated. We believe that the model application developed provides a simple alternative to summarize in meaningful parameters that characterize the response, it facilitates rigorous comparisons among the effects of different compounds and experimental approaches and it helps to comprehend multi-variable scenariosThe authors wish to thank CSIC (Intramural project: 200930I183) and Ministerio de Ciencia e Innovación (project CTM2010-18411, co-financed with FEDER funds by European Union) for financial support. Miguel Angel Prieto Lage was awarded one grant from the JAE predoctoral program co-financed by the CSIC and European Social Fund (ESF)Peer reviewe

Optimization of nutrient concentration for citric acid production by solid-state culture of Aspergillus niger on polyurethane foams

8 páginas, 6 tablas, 6 figurasCitric acid production from mussel processing effluents by Aspergillus niger in solid-state culture was studied using polyurethane foam particles soaked with the culture medium. Conditions were used that allowed comparison of the results with those obtained before in submerged culture and the attribution of the differences to the characteristics of solid-state culture. A screening of several strains gave different results than in submerged culture and a reduction in the incubation time. The joint effect of nitrogen and phosphorus initial concentrations was examined by means of orthogonal factorial designs in five selected strains. The results showed that different requirements of N and P for each individual strain were needed. Optimization was done using different experimental strategies for two selected strains. Following either the direction of the linear approximation gradient of the first-order empirical model obtained or with a new rotatable factorial design, an optimum value could be obtained. In comparison with previous results in submerged culture, the strains with high requirements of N and P seemed to be disfavored in solid-state culture. The ones with low requirements were favored and showed a bigger tolerance to a surplus of both nutrients.J. Pintado thanks Caixavigo (Spain) for the research fellowship.Peer reviewe

Interactions affecting gibberellic acid production in solid-state culture: A factorial study

7 páginas, 6 figuras, 2 tablasThe production of GA3 in solid-state culture was studied using systems composed of maize cob particles soaked in an amylaceous efluent, as a function of three variables-particle diameter, volume of liquid phase, and substrate concentration-with a determinant influence on the response. The empirical model obtained provides an explanation of the behavior of the system in terms of a series of interactions with underlying problems of water activity and mass transfer, that can, however, be manipulated in a simple and reproducible manner. This model also allows the suitable orientation of production improvement, the interpretation of the mechanism of substrate inhibition detected, as well as means of correcting it without reducing the initial concentration of the substrate, and leads to an 11 -fold increase in the production obtained in the preliminary assays.The authors thank CICYT and Xunta de Galicia for their financial support (projects ALI 789-90, AMB 93-O 136, and XUGA-40204B-92).Peer reviewe

Amylase production by solid state culture of Aspergillus oryzae on polyurethane foams. Some mechanistic approaches from an empirical model

8 páginas, 6 figuras, 4 tablasUsing systems formed by particles of polyurethane foam of different densities soaked in an amylaceous effluent, the production of amylases by Aspergillus oryzae in solid state culture was studied by a complete factorial plan with four variables -- support density, particle diameter, volume of liquid phase and substrate concentration. The empirical model obtained is consistent and allows a simple control of the response, superior in several respects to that of the corresponding submerged cultures. Moreover, it enables a mechanistic approach to the behaviour of the system, whose principal kinetic characteristics can be interpreted in terms of intra- and interparticular diffusional effects, which have a determining influence on basic state variables, such as water activity and gas transfer.The authors would like to thank CICYT and Xunta de Galicia for their financial support (projects AMB 93-0136 and XUGA-40204B-92).Peer reviewe

Recovery of Proteolytic and Collagenolytic Activities from Viscera By-products of Rayfish (Raja clavata)

The aim of this work was to study the recovery of proteolytic and collagenolytic activities from rayfish (Raja clavata) viscera wastes. Initially, different parts of the gastrointestinal tract by-products (stomach, duodenum section including pancreas, final intestine) were evaluated. The extracts from proximal intestine yielded the highest values of both enzymatic activities. Optimal conditions for protease activity quantification were established at pH = 6, T = 40 °C and incubation time ≤20 min. The mathematical equation used to model the joint effect of pH and temperature led to maximum activity at pH = 8.66 and 59.4 °C, respectively. Overcooled acetone was found to be best option for recovery of enzymatic activities in comparison with ethanol, PEG-4000, ammonium sulphate and ultrafiltration system. Finally, a simple and systematic protocol of partial purification and total recovery of proteases and collagenases was defined

Biphasic toxicodynamic features of some antimicrobial agents on microbial growth: a dynamic mathematical model and its implications on hormesis

<p>Abstract</p> <p>Background</p> <p>In the present work, we describe a group of anomalous dose-response (DR) profiles and develop a dynamic model that is able to explain them. Responses were obtained from conventional assays of three antimicrobial agents (nisin, pediocin and phenol) against two microorganisms (<it>Carnobacterium piscicola </it>and <it>Leuconostoc mesenteroides</it>).</p> <p>Results</p> <p>Some of these anomalous profiles show biphasic trends which are usually attributed to hormetic responses. But they can also be explained as the result of the time-course of the response from a microbial population with a bimodal distribution of sensitivity to an effector, and there is evidence suggesting this last origin. In light of interest in the hormetic phenomenology and the possibility of confusing it with other phenomena, especially in the bioassay of complex materials we try to define some criteria which allow us to distinguish between <it>sensu stricto </it>hormesis and biphasic responses due to other causes. Finally, we discuss some problems concerning the metric of the dose in connection with the exposure time, and we make a cautionary suggestion about the use of bacteriocins as antimicrobial agents.</p> <p>Conclusions</p> <p>The mathematical model proposed, which combines the basis of DR theory with microbial growth kinetics, can generate and explain all types of anomalous experimental profiles. These profiles could also be described in a simpler way by means of bisigmoidal equations. Such equations could be successfully used in a microbiology and toxicology context to discriminate between hormesis and other biphasic phenomena.</p