Headline: Inhibition of pathogenic microbiota SUMMARYThe concrete nature of the probiotic effects that the presence of microorganisms (especially lactic acid bacteria: LAB) exercise on larval cultures of fish, it is not well defined, being been able to attribute to different factors or action mechanisms. In fact, the production of diverse antibacterial metabolites (bacteriocins in particular) by many LAB forms are able to constitute the basis of these probiotic effects, as repeatedly described in the literature. Accordingly, the inhibition of fish pathogenic species by extracts of LAB constitutes a rapid method for detecting potential probiotics. By studying the response of four common pathogens of turbot (Scophthalmus maximus) to nine potential probiotics, the diversity and mechanisms of effectors in the probiotics were demonstrated to present complex profiles dose-response and non-treatable with conventional models. Proposed modifications allow satisfactory fits and the calculation of useful parameters in the comparison of activities. The results showed that lactic and acetic acid, and not the bacteriocins, are responsible for effects (inhibitory or stimulatory depending on the concentrations considered) in all the cases studied.
Taking as a starting point a set of simple quantitative hypotheses regarding the possible relationships between cell receptors and effector molecules, a statistical algorithm or generative model is developed that simulates different types of dose-response profiles and whose results are used in two ways, both subject to empirical verification. In the first of these, the suitability of several common descriptive models for the study of dose-response relationships is discussed, and changes are introduced that improve their suitability for this conceptual framework, generalise their application and lead to the systematisation of possible interactions between more than one effector, as well as between the effects of self-stimulating and self-depressor mechanisms. Secondly, the generative model suggests the existence of some unexpected profiles and their possible explanations. Both the profiles and the hypotheses appear to be supported by experimental evidence.
We suggest a new and general model to describe the effects of temperature (T) and pH on the catalytic activity of enzymes. Despite the abundance of models to describe those effects, the current proposals are unsatisfactory, except for specific experimental cases in which the interactive mechanism between the two variables does not exist. For both variables, our solution analyses the activated and deactivated phases of an enzyme as phenomena of different nature. The system is described with independent probability functions. The interactive effects between T and pH are introduced with simple auxiliary functions. These functions describe the variations induced by each variable in the parameters that define the effects of the other. The structure of the resulting equation is, in theory and practice, very regular, which facilitates its use, and it is highly descriptive in different scenarios with or without interactive effects. The model was tested on three different enzymatic systems which are specifically designed to produce data for the evaluation of the effect of T and pH on the enzyme activity (A). Afterwards, our model was validated using results from other authors. Briefly, the authors found that: (1) other available models that were compared with our proposal were inefficient and in all cases our model provided the only statistically consistent solution; (2) in four cases, the enzymatic activity could only be explained if interactive effects are accepted; (3) synergy and antagonism concepts for the interaction between T and pH were described and classified; and (4) our solution is universal and independent of the structure of an enzyme and the reaction concerned.
BACKGROUND: The high oxygen availability in solid‐state cultures makes them especially suitable for fungal enzyme production. Glycogen‐rich mussel processing wastewaters have been used successfully as substrates for amylase production by Aspegillus oryzae in solid‐state cultures supported in polyurethane foam. The aim of this work was to study the fed‐batch mode in a scalable solid‐state bioreactor to extend the productive period and obtain high amylase production. Culture salinization due to the NaCl content of these wastewaters is the main drawback. RESULTS: Evaporation of the excess liquid added during feeding led to progressive salt accumulation. The effect of culture salinization on amylase production was analysed and mathematically modelled, and the IC50 (65.4 g L−1 of NaCl) was calculated. An optimum operation mode for this bioreactor was designed that included foam extrusion for removing the incubated medium, washing and a final recharge with fresh medium every 72 h of incubation. This procedure kept the salt concentration under IC50 and increased the amylase production from 3000 to 12 000 UE g−1. CONCLUSION: An operating mode with intermittent extrusions and washings of the support between feedings was found to be an appropriate procedure for preventing the accumulation of inhibitory compounds in fed‐batch solid‐state cultures. © 2012 Society of Chemical Industry
Benthic dinoflagellates of the genus Ostreopsis are important components of subtropical and tropical marine coral reef-lagoonal environments. Currently, as a result of global warming and trade globalization, they are also distributed worldwide. These microalgae are shown to produce palytoxin, one of the most potent non-protein marine toxins known.The haemolytic assay is a very easy, rapid and sensitive method to determine palytoxin. However, under the conditions reported in previous works this assay is inadequate for a rigorous dose-response treatment, since: (1) it produces degenerate sigmoidal profiles, with a pronounced slope which makes the calculation of the ED 50 very sensitive to the experimental error; (2) at the usual work temperature, the in vitro stability of the system is low, which accentuates the variability and ambiguity of the response. To resolve these problems haemolysis of sheep erythrocytes is studied, including it's toxicological dynamics, kinetics, inhibition by ouabain and response to temperature. The results show that, to obtain a smoother, more stable and reproducible response, it is necessary to apply two resources simultaneously: operation at a moderate temperature and partial inhibition of the palytoxin by ouabain. It also produces highly reliable parameters and allows strict equivalencies to be established with the mouse bioassays, a traditional reference point, though bioethically questionable and 20 times less sensitive than the bioassay proposed here. #
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