On the choice of the optimal periodic operation for a continuous fermentation process

In this contribution we investigate the impact of the forcing waveform on the productivity of a continuous bioreactor governed by an unstructured, nonlinear kinetic model. The (periodic) forcing is applied on the substrate concentration in the feed. To this end, some alternative waveforms commonly encountered in practice are evaluated and their performance is compared. An analytical/numerical approach is used. The preliminary analytical step is based on the π‐criterion that gives useful information for small amplitudes. The extension to larger amplitudes, when significant improvements are expected, is then performed through a continuation‐optimization procedure. It is found that the choice of the specific waveform has an impact on the performance of the process and there is no unique best forcing for any process condition, but its choice depends on the operating parameters and the forcing amplitude and frequency values. Further, the influence of the waveform functions on the wash‐out conditions are extensively examined. The analysis shows that all the waveforms examined in this work may lead to significant enlargement of the nontrivial regime with respect to a steady state operation. In particular, square‐wave forcing leads in practice to the extinction of the wash‐out conditions for any feed substrate concentration and for a well defined choice of the forcing parameters. © 2010 American Institute of Chemical Engineers Biotechnol. Prog., 2010     

A chemically-defined medium for production of compactin by Penicillium citrinum

A mutant strain of Penicillium citrinum grown in a chemically-defined production medium, yielded 145 mg compactin l^–1. The medium also facilitated spectrophotometric analysis of compactin. Addition of KH₂PO₄in the production medium did not increase the compactin production, while addition of a surfactant, Tween 80, increased compactin to 175 mg l^–1. Inoculation with 10⁷ spores ml^–1 and initial pH of 6.5–7 were the most suitable for compactin production.     

Aspects Affecting Biosynthesis and Biotransformation of Secondary Metabolites in Plant Cell Cultures

Abstract

Biosensors are useful analytical devices that can be integrated with on-line process monitoring schemes. In this article, the principles and applications of these devices for bioprocess monitoring are considered. Several different types of biosensors are described, and the applications and limitations of flow injection analysis (FIA) for these applications are discussed. It is hoped that the background provided here can be useful to researchers in this area.     

Viability, strength, and fragmentation of Saccharopolyspora erythraea in submerged fermentation.

Two fermentations of the commercially important erythromycin-producing filamentous bacterium Saccharopolyspora erythraea were conducted in defined media. One was glucose-limited and the other nitrate-limited. The viability of the hyphae was determined using the fluorescent stain BacLight (Molecular Probes, Eugene, OR). Also, the force required to strain hyphae to breakage was determined using micromanipulation and a sensitive force transducer. In both fermentations, fragmentation coincided with the appearance of regions in the mycelia with permeabilised membranes (considered nonviable). Under glucose-limitation, hyphal breaking force rose to 1,050 +/- 130 nN at the end of the growth phase and fell to an undetectable value as a result of glucose exhaustion. Under nitrate-limitation, hyphal breaking force fell from 900 +/- 160 nN during the growth phase to 550 +/- 40 nN in the stationary phase. In both cases image analysis showed that the dimensions of mycelia were of the same order, suggesting that the major factor influencing fragmentation was the appearance of nonviable regions (assumed to be weak). The location in which nonviable regions first appear within hyphae could not be determined because of their appearance coinciding with fragmentation.     

Thermoanaerobium lactoethylicum spec. nov. a new anaerobic bacterium from a hot spring of Kamchatka

A new anaerobic thermophilic Gram-positive, nonsporeforming bacterium strain ZE-1 was isolated from a hot spring of Kamchatka (USSR). The cells are rod-shaped, (0.5–0.8 · 2.0–20 m), non-motile. The bacterium can grow between 42 and 75°C; the optimal temperature is 65°C. The growth is possible between pH values 5.0 and 8.5; optimal pH is 7.0. The cultures grow on the media containing peptone, yeast extract, or casein hydrolysate as nitrogen sources in the presence of glucose or some other sugars, mannitol or starch. The main fermentation products of glucose are ethanol, acetate, lactate, H₂, CO₂; byproducts are propionic, butyric and isovaleric acids. Glucose is metabolized via Embden-Meyerhoff-Parnas pathway. Molecular hydrogen does not inhibit growth. The bacterium does not reduce aceton to isopropanol, but is able to form H₂S from elemental sulfur. The bacterium contains a soluble hydrogenase. This enzyme catalyzes both evolution and uptake of H₂ and is active in the presence of methyl viologen. The DNA-base composition is 34.6 mol%; the genome size 2.08x10⁹ D. The name proposed for the isolated bacterium strain ZE-1 is Thermoanaerobium lactoethylicum spec. nov.     

New motile anaerobic bacteria growing by succinate decarboxylation to propionate

Three strains of new anaerobic, gram-negative bacteria which grew with succinate as sole source of carbon and energy were isolated from anoxic marine and freshwater mud samples. Cells of the three strains were small, non-spore-forming, motile rods or spirilla. The guanine-plus-cytosine content of the DNA of strain US2 was 52.6±1.0 mol%, of strain Ft2 63.5±1.4 mol%, and of strain Ft1 62.6±1.0 mol%. Succinate was fermented stoichiometrically to propionate and carbon dioxide. The growth yields were 1.2–2.6 g dry cell mass per mol succinate degraded. Strains US2 and Ft2 required 0.05% w/v yeast extract in addition to succinate for reproducible growth. Optimal growth occurred at 30°–37°C and pH 6.8–8.0. Addition of acetate as cosubstrate did not stimulate growth with any strain. Strain Ft2 grew only under strictly anaerobic conditions, whereas strains US2 and Ft1 tolerated oxygen up to 20% in the headspace. Strains US2 and Ft2 grew only with succinate. Strain Ft1 also converted fumarate, aspartate, and sugars to propionate and acetate. This strain also oxidized propionate with nitrate to acetate. Very low amounts of a c-type cytochrome were detected in propionate plus nitrate- or glucose-grown cells of this strain (0.4 g x g protein^-1). Moderate activities of avidin-sensitive methylmalonyl-CoA decarboxylase were found in cell-free extracts of all strains.     

A rod-shaped,gram-negative,propionigenic bacterium with a wide substrate range and the ability to fix molecular nitrogen

From estuarine mud a rod-shaped, motile, gram-negative, anaerobic bacterium was isolated (strain asp 66). Asp 66 fermented several substrates including glucose, fructose, malate, fumarate, citrate and aspartate. Fermentation products were acetate, propionate and presumably CO₂. Hydrogen was never formed nor utilized. Succinate conversion to propionate was catalyzed by cell suspensions but did not support growth. Asp 66 did not require vitamins and grew well in mineral media with a fermentable substrate. The pH range for growth was from 6.5 to 8.5. Temperature optimum was 27 to 30°C. The strain was able to fix N₂ as evidenced by its growth with N₂ as sole nitrogen source and its ability to reduce acetylene to ethylene. Cell-free extracts of cultures grown under air without shaking contained cytochrome(s) with absorption peaks at 523 nm and at 553 nm. The G+C content of the DNA was 60.8+-1 mol%. The taxonomic position of strain asp 66 is discussed.     

Ethanol production from xylose by Thermoanaerobacter ethanolicus in batch and continuous culture

The fermentation of xylose by Thermoanaerobacter ethanolicus ATCC 31938 was studied in pH-controlled batch and continuous cultures. In batch culture, a dependency of growth rate, product yield, and product distribution upon xylose concentration was observed. With 27 mM xylose media, an ethanol yield of 1.3 mol ethanol/mol xylose (78% of maximum theoretical yield) was typically obtained. With the same media, xylose-limited growth in continuous culture could be achieved with a volumetric productivity of 0.50 g ethanol/liter h and a yield of 0.42 g ethanol/g xylose (1.37 mol ethanol/mol xylose). With extended operation of the chemostat, variation in xylose uptake and a decline in ethanol yield was seen. Instability with respect to fermentation performance was attributed to a selection for mutant populations with different metabolic characteristics. Ethanol production in these T. ethanolicus systems was compared with xylose-to-ethanol conversions of other organisms. Relative to the other systems, T. ethanolicus offers the advantages of a high ethanol yield at low xylose concentrations in batch culture and of a rapid growth rate. Its disadvantages include a lower ethanol yield at higher xylose concentrations in batch culture and an instability of fermentation characteristics in continuous culture.