Nitrification of ammonia in concentrated waste streams is gaining a lot of attention nowadays. Nitrosomonas europaea is the predominant ammoniaoxidizing species in these environments. Prediction of the behaviour of a pure culture of N. europaea (ATCC 19718) under conditions prevailing in concentrated waste streams was the aim of this study. The initial oxygen consumption rate of a concentrated cell suspension was used as a rapid assay to measure the effects on N. europaea under various conditions. Several relationships, based on Michaelis-Menten kinetics, were derived. They describe the behaviour of N. europaea at substrate (NH~), product (NO~-) and K +, Na ÷, SO~-, NO~-, C1-concentrations up to 500 mol/m ~ and pHs ranging from 6.5 to 8.5. High concentrations of ions inhibited N. europaea but specific substrate inhibition was not observed. Product inhibition was strongly pH-dependent and severe inhibition was found at pH 6.5.

-Propionibacteria are able to produce a wide variety of food components that are benificial to the human health. First of all, because of its unique metabolism, Propionibacterium contains a wide variety of co-factors, mainly involved in transfer and rearrangement of C1-compounds. This microorganism has been known for decades as an efficient vitamin B 12 (deoxy adenosyl cobalamin) producer. In this contribution, a new fermentation strategy is described leading to fermentation broths with high levels of this vitamin. In addition, some strains within the Propionibacterium genus can produce large amounts of folic acid. Other potential beneficial or nutritional ingredients produced by these bacteria are anti-microbial compounds such as propionic acid and bacteriocins. Propionic acid is reported to have potent growth-inhibiting effects on fungi and as such the Propionibacterium fermentation has great potential in food preservation. In addition, several bacteriocins have been found to be produced by these bacteria such as propionicin PLG-1 and jenseniin G, acting against a variety of Gram(+) bacteria. Finally, the production of high (intracellular) levels of the low-calorie sugar trehalose is reported. This sugar, presumably, functions as compatible solute in this bacterium and certain strains accumulate huge amounts under selected conditions. The possibility for application of this metabolism are discussed.Propionibacterium / folate / vitamin B 12 / trehalose / antimicrobial Résumé -Production de nutraceutiques par les bactéries propioniques. Les bactéries propioniques sont capables de produire une grande variété de composés alimentaires bénéfiques pour la santé humaine. En premier lieu, en raison de son métabolisme unique, Propionibacterium contient une grande variété de co-facteurs, principalement impliqués dans le transfert et le réarrangement de composés C1. Ce microorganisme a été reconnu depuis des décennies comme producteur efficace de vitamine B 12 (deoxy adenosyl cobalamine). Dans cet article, une nouvelle stratégie de fermentation est décrite conduisant à des bouillons de fermentation avec des niveaux élevés de cette vitamine. De plus, certaines souches dans le genre Propionibacterium peuvent produire de grandes quantités d'acide folique. D'autres ingrédients potentiellement bénéfiques ou nutritionnels produits par ces bactéries sont des composés anti-microbiens comme l'acide propionique et les bactériocines. L'acide propionique est décrit pour avoir des effets puissants d'inhibition de la croissance fongique, et de ce fait, la fermentation de Propionibacterium a de grandes potentialités en conservation des aliments. De plus, plusieurs bactériocines sont produites par ces bactéries telles que la propionicine PLG-1 et la jenseniine G, actives contre plusieurs bactéries Gram(+). Enfin, la production de niveaux élevés (intracellulaires) de tréhalose, sucre peu calorique, a été décrite. Ce sucre, probablement, fonctionne comme soluté compatible dans cette bactérie, et certaines souches accumulent de qua...

The relationship between fungal morphology and heterologous protein production was examined for an Aspergillus awamori strain during a series of fermentations with a batch phase followed by a fed-batch phase. Agitation rate and inoculation concentration were used as controlled variables to generate different fungal morphologies in 20-dm3 stirred tank reactors. Morphology was quantitatively characterized using Image Analysis. The different agitation rates and inoculum concentrations had large effects on the development in hyphal length and number of tips during the fermentations. A reduced inoculum concentration resulted in a more branched mycelium. The different agitation rates affected the morphology after 30 h of fermentation significantly but did not affect the start time of fragmentation. A 3-fold increase in hyphal length increased the apparent viscosity by a factor of 7. The observed morphological differences had only a limited effect on product formation, suggesting that the structural features such as hyphal length and number of tips are of less importance for product formation. The primary effect of morphology on product formation is due to viscosity.

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A dynamic model for two microbial species immobilized in a gel matrix is presented and validated with experiments. The model characterizes the nitrification of ammonia with Nitrosomonas europaea and Nitrobacter agilis co-immobilized in K-carrageenan gel beads. The model consists of kinetic equations for the microorganisms and mass transfer equations for the substrates and products inside and outside the gel beads. The model predicts reactor bulk concentrations together with the substrate consumption rate, product formation, and biomass growth inside the gel beads as a function of time. A 50-day experiment with immobilized cells in a 3.3-dm(3) air-lift loop reactor was carried out to validate the model. The parameter values for the model were obtained from literature and separate experiments. The experimentally determined reactor bulk concentrations and the biomass distribution of the two microorganisms in the gel beads were well predicted by the model. A sensitivity analysis of the model for the given initial values indicated the most relevant parameters to be the maximum specific growth rate of the microorganisms, the diffusion coefficient of oxygen, and the radius of the beads. The dynamic model provides a useful tool for further study and possible control of the nitrification process. (c) 1994 John Wiley & Sons, Inc.