J. Mirón

Diauxic production of glucose oxidase by Aspergillus niger in submerged culture: A dynamic model

On studying the production of glucose oxidase (GOD) by Aspergillus niger, we find that both growth and production are diauxic processes, with logistic and linear phases. The gluconic acid that is produced from glucose by means of enzyme action can therefore be considered as a useful source of carbon for growth, and does not interfere with the biosynthesis of GOD in spite of being a product of its activity. From a kinetic viewpoint, the enzyme is a primary metabolite, but this can only be proved by including the Luedeking and Piret equation in a dynamic model that takes into account the effects of hydrogen peroxide on GOD, as well as those of the catalase, which is also produced by the microorganism, on the hydrogen peroxide.

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.

Proteases production by two Vibrio species on residuals marine media

A comparative study was carried out on the growth and production of alkaline proteases by two Vibrio species using different marine peptones from fish viscera residues. The bacteria tested, Vibrio anguillarum and Vibrio splendidus, are producers of high levels of proteolytic enzymes which act as factors of virulence in fish cultures, causing high mortality rates. The kinetic assays and subsequent comparison with the parameters obtained from the adjustment to various mathematical models, highlighted the potential interest of the media formulated, for their possible production on an industrial scale, particularly the production of proteases by V. anguillarum growing in rainbow trout and squid peptones.

Enhancement of the bioproduction potential of an amylaceous effluent

Abstract The treatment of starchy effluents could provide the basis for a series of simultaneous or alternative bioproductions easily integrable into a system of greater economic attraction that the simple production of SCP. In order to define some of the possible options, this study uses an amylaceous effluent for simultaneous production of SCP and an amylolytic preparation which is partially consumed in the saccharification of a parallel flow of the same effluent concentrated by ultrafiltration with cutoff at 100 kD. With regard to the development of the above system, this paper describes the problems associated with ultrafiltration, the conditions that optimize saccharification of the concentrate and the requirements of various possible bioproductions that could be obtained from the saccharified concentrate.

Joint effect of nitrogen and phosphorus concentrations on citric acid production by different strains of Aspergillus niger grown on an effluent

SummaryThe joint effects of the initial concentration of N and P on the production of citric acid by 11 strains of Aspergillus niger on an effluent are studied by means of orthogonal full-factorial 22 designs. The results allow the definition of a series of empirical equations describing well differentiated types of behaviour. This demonstrates the usefulness of the procedure followed in order to establish selection criteria for the more suitable strains, to determine the tendencies that permit approaching optimum production and evaluate the viability of different culture options characterized by discontinuous feeding of one or another nutrient.

A HPLC method for specific determination ofα-amylase and glucoamylase in complex enzymatic preparations

SummaryIn the hydrolysis of soluble starch by mixtures of α-amylase and glucoamylase, the ratios maltose/glucose and maltoriose/glucose linearly depend, over a wide range, on the relation between both enzymes and are independent on the activity level of the enzymatic preparation. HPLC determination of hydrolysis products (glucose, maltose and maltotriose) of soluble starch by mixtures of these enzymes, after incubation under controlled conditions, is a rapid method for the evaluation of the relative levels of each enzyme in the mixtures. The method, first developed using pure commercial amylases, is applied, with consistent results, to cell free media ofAspergillus niger cultures on a glycogen-rich effluent.

Microfungus-yeast mixed cultures in the degradation of amylaceous wastes. I: Interactions affecting amylolytic activity

SummarySome possible criteria in selection of amylolytic microorganisms for their mixed culture with non-amylolytic yeasts are discussed, and the growth of several microfungus-yeast mixed cultures on mussel processing wastes are studied.

Alcoholic chestnut fermentation in mixed culture. Compatibility criteria between Aspergillus oryzae and Saccharomyces cerevisiae strains

The main objective of the present work consisted in the transfer to the case of the chestnut of a rice fermentative process that carried out to the Japanese traditional way to lead to an alcoholic bagasse, the moromi, capable of obtaining distilled. This way, selection assays of amylolitic Aspergillus oryzae strains and studies of compatibility between microfungi and yeast were carried out. These mixed cultivations were performed operating in batch submerged culture. Later on, using solid state system (chestnut, microfungi, yeast), a fermentative fed-batch process (koji, moto, moromi) was defined. By means of this approach a yield of 70% was reached in the conversion of total carbohydrates in ethanol. Also, the time required by the traditional operation was reduced in half.

A new device for measuring diffusional restrictions and modelling substrate inhibition in a starch-glucoamylase system

An experimental device that quantifies the diffusional properties of polysaccharides solution, in a simple and reproducible way, and an equation relating these properties to solute concentration, is proposed. Using this model to analyse the kinetic profile of the hydrolysis of starch with glucoamylase, is substrate inhibition completely reduced to phenomena that depends on the reological properties of the reacting mixture. The experimental device and kinetic model can be applied to contrast hypothetical substrate inhibitions in any enzymatic system.

Effects of spill-treating agents on growth kinetics of marine microalgae.

The effects of four spill-treating agents (STAs) (CytoSol, Finasol(®) OSR 51, Agma OSD 569 and OD4000) on the growth kinetics of three marine microalgae (Isochrysis galbana, Chaetoceros gracilis, Phaeodactylum tricornutum) were studied. Chlorophyll a concentration and optical density at 700 nm were assessed to describe the logistic growth of algae in batch cultures. The optical density data were initially analyzed as described for standard algal growth inhibition tests and subsequently modelled by a bivariate model, as a function of time and dose, to assess the toxic effects on growth parameters. Increasing trends in EC50 and EC10 values with time were found with the standard approach. In 8 of the 11 tests, the lag phase (λ) or the time required to achieve half the maximum biomass (τ) was significantly dependent on the STA concentration. A global parameter (EC50,τ) was calculated to summarize the effects of STAs on growth parameters in the bivariate model. The ranking of sensitivity as EC50,τ values was I. galbana>C. gracilis>P. tricornutum. For all species tested, the least toxic agent was Agma OSD 569, followed by CytoSol. The mathematical model allowed successful ecotoxicological evaluation of chemicals on microalgal growth.