Ma.P. González

A method for bacteriocin quantification

M.L. CABO, M.A. MURADO, M.P. GONZÁLEZ and L. PASTORIZA.1999.Different aspects of the most commonly used assay methods in the study of bacteriocins were examined. The conditions under which extraction and incubation (including exposure time) take place were analysed, and several different formal models that are usually employed to calculate ID50 were compared. As an alternative designed to overcome the problems which characterize the response of micro‐organisms that are sensitive to bacteriocins, an operative procedure in a liquid medium and a modified re‐parameterized logistic equation is proposed. When applied to the inhibition of Leuconostoc mesenteroides by nisin, the model allows an optimal experimental procedure to be defined.

Dose-response relationships: an overview, a generative model and its application to the verification of descriptive models

Abstract 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 (DR) 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 DR 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.

Characterization of microbial biomasses and amylolytic preparations obtained from mussel processing waste treatment

This work describes a treatment of glycogen-rich wastes from industrial mussel processing, involving the production of a protein fraction and a medium suitable for the culture of amylolytic microfungi. A strain of Aspergillus oryzae was chosen which allows the simultaneous production of single cell protein and a highly stable amylolytic preparation. The characteristics of the biomass obtained (proportion and in vitro digestibility of the proteins, levels of essential amino acids and nucleic acids, types of fatty acids present) were shown to be suitable, in principle, for animal feeds. The amylolytic preparation, obtained by ultrafiltration (with cut-off at 30 kD) of the cell-free medium, was very similar to commercial α-amylase preparations, containing mainly α-amylase, together with a small proportion of glucoamylase.

Depuration and valuation of mussel-processing wastes. Characterization of amylolytic postincubates from different species grown on an effluent

Abstract Mussel-processing wastes, which contain glycogen (≈ 10 g/litre) as their main component, can be used as a culture medium for several species of amylolytic yeasts and microfungi useful as single cell protein (SCP) sources. In addition, cell-free media from these cultures (with COD reduced to ≈ 10% of its initial value) could, in principle, be used for the hydrolysis of greater volumes of the same effluent, which could then be concentrated, converting it into a more versatile microbial substrate. With this objective in mind, the optimal reaction conditions, stability and kinetics of postincubates from several amylolytic species with distinct growth features when cultured on the effluent, were examined. Some of the mechanisms involved in the regulation of amylolytic activity are also discussed, as well as some of the methodological problems often associated with this kind of study.

An empirical model for describing the effects of nitrogen sources on nisin production

Aims: A study on the effects of tryptone and yeast extract on nisin production by Lactococcus lactis was carried out using a second order rotatable factorial design.

Production of gibberellic acid from mussel processing wastes in submerged batch culture

Abstract Mussel processing wastes (MPW), after being concentrated by ultrafiltration (100 KD) and partially hydrolyzed (with amylase from Aspergillus oryzae cultures on raw wastes), are transformed into a substrate suitable for diverse bioproductions, one being gibberellic acid, whose production is known to be closely related to the level of N in the culture medium. Given the nature of the principal nutrients present in the wastes (glycogen and proteins as carbon and nitrogen sources, respectively), in order to obtain a reasonable production of the hormone with minimum previous treatment of the medium, various aspects of the relationships between the types of nutrients and their balances, particularly in the trophopase, were studied. In this respect, compared to glucose the use of polysaccharides promoted a brief but intense alkalinization phase and the appearance of N-limitation at a greater level of remaining carbohydrate. On the other hand, although the type of C-source imposed differences on the requirements for N, the consumption rate of the latter seemed to be invariant under the conditions studied, the variable factor being the consumption rate of the C-source.

Substrate inhibition of Pediococcus acidilactici by glucose on a waste medium. Simulations and experimental results

Aims: The possibility of substrate inhibition by glucose on biomass and pediocin production was studied in cultures of Pediococcus acidilactici on a residual medium.

Survival of lactic acid bacteria in seawater: a factorial study.

A feasibility study of lactic bacteria as potential probiotics in larval cultures of marine fish was performed by investigating the survival of five strains of lactic bacteria in seawater by readily standardized procedures at different temperatures and salinities. These conditions were chosen in such a way that their combinations define a complete first-order factorial design. Depending on the strain and the ambient conditions, the survival adhered to first-order kinetics in some cases, and to the Gompertz equation in others. The half lives (t0.5) calculated from these models were subsequently introduced as responses to the factorial designs, estimating the coefficients of empirical equations that describe the group effect of temperature and salinity on t0.5. Simply additive effects were found in two cases, a negative first-order interaction in another case, while another two required second-order models.

Dose–response relationships. A model for describing interactions, and its application to the combined effect of nisin and lactic acid on Leuconostoc mesenteroides

As well as producing bacteriocins, many lactic bacteria produce other potentially toxic compounds or growth inhibitors, especially lactic acid, which may interfere in the assays commonly used to quantify these peptides. A systematic set of modifications is proposed which, when applied to the logistical equation, enable it to describe the combined (but not additive) effects of two or more active principles. The general model thus derived is applied to the interaction of nisin and lactic acid on Leuconostoc mesenteroides.

Interactions between pretreatment and nutrient concentrations of mussel processing effluents for citric acid production

Abstract Pretreatment of mussel processing effluents for citric acid production by Aspergillus niger (CBS 262-65) in submerged culture was studied by means of an orthogonal full factorial experimental design with four independent variables: initial levels of hexacyanoferrate II, methanol, phosphate, and carbon source. The empirical model thus obtained showed the ineffectiveness of the hexacyanoferrate treatment (contrarily that occurs with molasses) and at the same time, a series of complex interactions affecting the acid production not described in previous studies concerned by the separate effects of the variables here considered. Basically, the main effect of the hexacyanoferrate is toxic while the presence of methanol seems to involve morphological changes that increase the superficial area of the mycelial pellets, thereby promoting an unspecific metabolic activation. It therefore enhances the toxic effect of hexacyanoferrate, but also favors citric acid accumulation. The net response depends on the concentrations of the carbon source and phosphorus.