Jorge Arcas

Bacillus thuringiensis growth, sporulation and δ-endotoxin production in oxygen limited and non-limited cultures.

The production of crystals and spores ofBacillus thuringiensis var.israelensis was studied under different aeration conditions. The results with 4 l batch cultures showed that for O2 non-limited, cultures cell yield, toxin production and spore count were constant for all oxygen transfer rates (OTR). Under O2 limitation, °-endotoxin concentrations and spore counts were lower than those obtained in non-limited cultures. In addition, δ-endotoxin yields diminished under O2 limitation, suggesting that the toxin synthesis mechanism could have been affected.

High level of sporulation of Metarhizium anisopliae in a medium containing by-products

SummarySolid-state fermentation of rice bran or rice-bran-husk mixtures byMetarhizium anisopliae proved to be highly successful in spore yield. Optimum sporulation response on bran medium occurred when the initial water activity values ranged from 0.982 to 0.999. When bran was supplemented with 50% rice husk, the spore yield almost doubled, but a narrower initial water activity range (0.997–0.999) was optimum. Under these conditions, spore yields were 5–15 times higher (depending on the strain) than those currently obtained on the basis of rice grain fermentations.

Characterization of growth and sporulation of Metarhizium anisopliae in solid-substrate fermentation

The entomopathogenic fungus Metarhizium anisopliae was cultivated by solid-substrate fermentation both with and without forced aeration using a medium based on a mixture of rice bran and rice husk; the water activity was fixed at an initial value of 0.998. An equation to describe the growth and sporulation processes was derived from stoichiometric considerations. By means of elemental mass balances and using the concept of c-mole, the stoichiometric coefficients of the growth equation were determined. It was concluded that under the culture conditions tested, M. anisopliae can grow at a maximum specific growth rate of 0.08 h−1. After 90–100 h of culture when growth has stopped, a spore yield of 2.3 × 1010 spores g−1 rice bran was obtained. This is as high as 80.4% of the maximum theoretical value. The heat generated during the culture did not affect growth and sporulation since, even when high initial amounts of solids were used, no desiccation was observed. Nevertheless, the yields obtained under these conditions suggested the appearance of another type of growth limitation not related to substrate consumption.

Bioinsecticidal activity of conidia and dry mycelium preparations of two isolates of Beauveria bassiana against the sugarcane borer Diatraea saccharalis

Two isolates of Beauveria bassiana (Bb1 and Bb5 strains) were grown in solid-state and submerged cultures (SSC and SbC, respectively) in order to obtain conidia and dry mycelium preparations. The samples obtained at laboratory scale were tested as alternatives for their further use as mycoinsecticides to control the sugarcane borer Diatraea saccharalis. The spore yields obtained in SSC indicated that the Bb5 strain was able to produce around three times more conidia per gram of initial dry matter (3.7×1010) than the Bb1 strain (1.3×1010) in a solid medium composed of wheat bran and bran husk. Under this culture conditions, the former showed not only satisfactory spore yields, but also a higher bioinsecticidal activity than the latter. Laboratory bioassays carried out with conidia of both strains against D. saccharalis larvae indicated that the Bb5 strain promotes an insect mortality of 82.5% whereas only 21.3% was observed with the Bb1 strain preparations. Concerning the samples obtained in SbC, in which a culture medium based on glucose and yeast extract was employed, it is interesting to point out that although both strains showed similar behaviors with yields of approximately 1.50×1010 conidia per gram of dry mycelium, both preparations failed in their bioinsecticidal activities. Despite satisfactory yields, bioinsecticidal activity of the Bb1 and Bb5 strains dropped drastically showing a larvae mortality below 2%.

Water balance in solid-state fermentation without forced aeration

Abstract Water balances, based on the evaluation of water released from the fermentor, were estimated in a solid-state fermentation process performed without forced aeration. It was proved that the net gain or loss of water during the course of the process depends on the dry weight of the solid substrate at the beginning of the process and also on the initial water activity. A linear relationship was found between the wet weight losses of cultures recorded after the end of the growth period and the initial dry weight of the substrate which enables the evaluation of the water released from the vessels. These values were included into water balances from which it was possible to calculate the water produced by metabolism of carbohydrates, which was estimated at 0.40 mol of H 2 O per C-mol of glucose consumed.

Data reconciliation and gross error diagnosis based on regression

Abstract In this article we show that the linear reconciliation problem can be represented by a standard multiple linear regression model. The appropriate criteria for redundancy, determinability and gross error detection are shown to follow in a straightforward manner from the standard theory of linear least squares. The regression approach suggests a natural measure of the redundancy of an observation. This approach yields also an explicit expression for the probability of detecting a gross error in an observation, which depends on its redundancy. The criterion for the detection of gross errors derived from the regression model is shown to yield the maximum probability of correct outlier identification. We consider two examples analyzed in the literature to demonstrate how our approach allows a complete understanding of the main data features.

Environmental Solid-State Cultivation Processes and Bioreactors

Solid-state cultivation involves the growth of microorganisms in beds of moist solid particles that have a minimum of free water between the particles. The chapter describes environmentally-related solid-state cultivation processes. For example, some processes use substrates that are residues of agriculture, forestry, or food-processing, thereby reducing the environmental impact of the residue. Other processes do not use residues, but produce products that have environmental applications. Still other processes use environmental-friendly biotransformations that have the potential to replace current industrial processes. Finally, some solid-state cultivation processes can be used to remove pollutants from soil or waste streams. Typically, environmental applications of solid-state cultivation involve large-scale processing of organic solids. The current chapter addresses the design and operation of bioreactors for these processes. It shows how the various bioreactor types can be classified according to the aeration strategy, namely whether the bed of solids is forcefully aerated or not, and according to the agitation strategy, namely the frequency of mixing of the bed of solids. It discusses the current state-of-the-art in optimizing the design and operation of the various bioreactor types, showing how mathematical models that combine microbial growth kinetics and heat and mass transfer phenomena are the most powerful tools that we have available for this task. The chapter concludes by highlighting the necessity to convert current mathematical models into user-friendly computer programs that can guide design and operation decisions for large-scale solid-state cultivation bioreactors.