Abstract: Lignocellulosic materials containing cellulose, hemicellulose, and lignin as their main constituents are the most abundant renewable organic resource present on Earth The conversion of both cellulose and hemicellulose for production of fuel ethanol is being studied intensively with a view to develop a technically and economically viable bioprocess The fermentation of glucose, the main constituent of cellulose hydrolyzate, to ethanol can be carried out efficiently On the other hand, although bioconversion of xylose, the main pentose sugar obtained on hydrolysis of hemicellulose, to ethanol presents a biochemical challenge, especially if it is present along with glucose, it needs to be fermented to make the biomass-to-ethanol process economical A lot of attention therefore has been focussed on the utilization of both glucose and xylose to ethanol Accordingly, while describing the advancements that have taken place to get xylose converted efficiently to ethanol by xylose-fermenting organisms, the review deals mainly with the strategies that have been put forward for bioconversion of both the sugars to achieve high ethanol concentration, yield, and productivity The approaches, which include the use of (1) xylose-fermenting yeasts alone, (2) xylose isomerase enzyme as well as yeast, (3) immobilized enzymes and cells, and (4) sequential fermentation and co-culture process are described with respect to their underlying concepts and major limitations Genetic improvements in the cultures have been made either to enlarge the range of substrate utilization or to channel metabolic intermediates specifically toward ethanol These contributions represent real significant advancements in the field and have also been adequately dealt with from the point of view of their impact on utilization of both cellulose and hemicellulose sugars to ethanol

Abstract: In order to remove or reduce the concentrations of toxic substances present in the sugarcane bagasse hemicellulose hydrolysate for xylose-to-xylitol bioconversion, the hydrolysate was pretreated by changing the initial pH level through the combination of different bases and acids with or without the subsequent addition of activated charcoal. Attention was given to the influence of the fermentation time as well.

Abstract: Lignocellulosic residues obtained from crops cultivation form useful sources to be used as substrate for bioconversion processes. Sugarcane bagasse, which is a complex substrate obtained from the processing of sugar cane, is an important biomass among such sources. Due to its abundant availability, it can serve as an ideal substrate for microbial processes for the production of value added products. This paper reviews recent developments on biological processes developed on production of various products in solid state fermentation using sugarcane bagasse as the substrate and describes production of protein enriched feed, enzymes, amino acid, organic acids and compounds of pharmaceutical importance, etc. through microbial means.

Abstract: Many pseudomonads and other bacteria can grow on aliphatic and aromatic hydrocarbons that occur in the environment. We are examining the potential of such organisms as biocatalysts for the oxidation of a variety of substituted aliphatic and aromatic compounds. To attain a high production rate of oxidation products via such biotransformations, we have focused on two-liquid phase culture systems. In these systems, cells are grown in liquid media consisting of an aqueous phase containing water-soluble growth substrates and droplets of a water-immiscible organic solvent containing bioconversion substrates and products. For industrial applications of such two-liquid phase processes, several questions remain. What are the maximum rates at which apolar compounds can be transferred from the apolar phase to cells growing in the aqueous phase, i.e., what are the maximum space-time yields attainable in two-liquid phase fermentations under practical conditions? What does an efficient downstream processing of two-liquid phase medium involve? What safety regimes should be considered in working with flammable organic solvents? Can elevated pressure be used to increase oxygen transfer? Based on answers to these questions, we have recently developed a high-pressure, explosion-proof bioreactor system with Bioengineering AG (Wald, Switzerland), which will be installed in our pilot plant and used to explore two-liquid phase bioconversions at a pilot scale.

Abstract: A method of bioconversion of organic industrial or agricultural cellulose containing wastes into proteinaceous product. The method comprises comminution of the wastes with moistening and addition of a starting culture inducing their biological degradation and conversion into simple carbohydrates. The carbohydrates are fermented into digestible products. The starting culture comprises cleaving enzymes produced by edible microorganisms such as fungus and bacteria selected from the group consisting of Humicola grisea, Trichoderma harzanum, Ruminococcus albus.

Abstract: Pseudomonas fluorescens BF13 is especially capable of promoting the formation of vanillic acid during ferulic acid degradation. We studied the possibility of enhancing the formation of this intermediary metabolite by using suspensions of cells at high density. The bioconversion of ferulic into vanillic acid was affected by several parameters, such as the concentration of the biomass, the amount of ferulic acid that was treated, the carbon source on which the biomass was grown. The optimal yield of vanillic acid was obtained with 6 mg/ml cells pre-grown on p-coumaric acid and 2 mg/ml ferulic acid. Under these conditions the bioconversion rate was 95% in 5 h. Therefore BF13 strain represents a valid biocatalyst for the preparative synthesis of vanillic acid.

Abstract: Membrane technology is penetrating the corn refining industry in a variety of applications. The largest single use to date is probably clarification of corn starch hydrolysates where it can substantially reduce operating and waste disposal costs. Bioproducts produced from dextrose by fermentation and/or enzymatic reactions are being concentrated, fractionated or purified to varying extents by several membrane technologies. These bioconversion reaction steps could also benefit by coupling the appropriate membrane to the reaction vessel or fermenter as a continuous membrane reactor. This has been shown to improve enzyme utilization and reduce reaction time in saccharification and improve fermentation productivity and reduce downstream costs in fermentation.

Abstract: Solid food processing wastes and by-products are cofermented with cheese whey to produce ethanol. The experimental procedure involves the use of an enzymatic process to convert starch and lactose into fermentable sugars. These reducing sugars are then fermented to alcohol by distiller’s dried yeast and a high-ethanol tolerant yeast, Saccharomyces cerevisiae. Cheese whey is used as a wetting agent and provides macro- and micronutrients for the microorganisms. Cofermenting food processing wastes with cheese whey, in the presence of high- and low-temperature enzymes, induces a 33-36% increase in alcohol yield. This procedure also significantly reduces the fermentation time from 60 to 12 h.

Abstract: The needs and problems existing in the field of cultivation systems and waste management concerning elements and energy, as well as pollution, health, environment, and economy are described. The lack of reproducible biofertilisers of high quality calls for an efficient use of organic waste as a renewable raw material. Each 100 000 inhabitants in Sweden generate organic waste with considerable economic values in terms of nitrogen, phosphorus, and potassium; US$ 600 000 from the organic fraction of municipal solid waste and US$ 900 000 from human excreta as liquid organic waste, meanwhile only US$ 160 000 is recovered from the sewage sludge after the wastewater has passed the wastewater treatment plants. Most of the existing systems for handling solid and liquid waste are of old-fashioned design and cause large losses of nutrient elements. Therefore, pollution of air, water, soil, and vegetation, mainly by emissions from organic uaste, continues. Bioconversion is microbial transformation and upgrading of various organic wastes to products of high value. The elements can be efficiently recycled in completely closed local bioconversion systems with subsystems for collection, pre-processing, processing, and application of end-products. Solid and liquid organic waste from the municipality can provide renewable raw material for manufacturing of reproducible biofertilisers and of biogas. Suggestions are made on how to improve the present situation by the re-orientation of technology. A scenario for bioconversion by the year 2010 is presented.

Abstract: The potential market for lactic acid as the feedstock for biodegradable polymers, oxygenated chemicals, and specialty chemicals is significant. L-lactic acid is often the desired enantiomer for such applications. However, stereospecific lactobacilli do not metabolize starch efficiently. In this work, Argonne researchers have developed a process to convert starchy feedstocks into L-lactic acid. The processing steps include starch recovery, continuous liquefaction, and simultaneous saccharification and fermentation. Over 100 g/L of lactic acid was produced in less than 48 h. The optical purity of the product was greater than 95%. This process has potential economical advantages over the conventional process.

Abstract: Leptomycin B (LMB), a secondary metabolite produced by Streptomyces sp. strain ATS 1287, with known antifungal and antitumor effects, inhibits the nucleo-cytoplasmic translocation of the human immunodeficiency virus type 1 regulatory protein Rev and exhibits significant antiproliferative activity. Since LMB itself turned out to be distinctly cytotoxic, a bioconversion screening with a selected set of 29 bacterial and 72 fungal strains was performed in order to obtain metabolites of LMB with reduced antiproliferative effects. Several derivatives of LMB, more polar than the parent compound and produced in yields of >5%, were detected. Liquid chromatography-mass spectroscopy analysis indicated the type of bioconversion. Fermentations (1-liter scale) of those strains with high rates of transformation were suitable for isolation and characterization of the most prominent metabolites. Thus, bioconversion of LMB with Aspergillus flavus ATCC 9170 and Emericella unguis ATCC 13431 served for isolation of the novel derivatives 26-hydroxy-LMB (30% was the concentration of the metabolite [with respect to LMB] used for bioconversion) and LMB-24-glutaminamide (90%), respectively. Streptomyces rimosus ATCC 28893 converted LMB into 4,11-dihydroxy-LMB (13%) and 2,3-dihydro-LMB (55%). Although the antiproliferative effects of the LMB metabolites could be reduced through microbial conversion, none of these metabolites inhibited the nuclear export of Rev better than LMB itself.

Abstract: Trapping by adsorption on hydrophobic porous polymers was used to selectively remove γ-decalactone from the complex bioconversion medium. Several sorbents were tested : activated carbon, and three porous polystyrene-type polymers (Porapak Q, Chromosorb 105, and Resin SM4). The sorption isotherms were determined in water and in a model bioconversion medium without microorganisms. In the last part of the study, the application to the production of γ-decalactone by Sporidiobolus salmonicolor was carried out. Hydrophobic porous adsorbents are compatible with the bioconversion and protect the yeast from the toxic effect of γ-decalactone.

Abstract: Mycobacterium sp. NRRL B-3805 cells immobilized on Celite were used to selectively cleave β -sitosterol to 4-androstene-3,17-dione (AD), with bis(2-ethylhexyl)phthalate as the bioconversion medium. The amount of water retained in the immobilization matrix proved to be a key parameter for biological activity retention, 0.5 to 0.8 g water/g dry support giving the best results. Mechanically stirred batch reactors were effectively used for sterol biotransformation, no increase in bioconversion rates being obtained for stirring speeds above 100 rpm. Kinetic studies were performed with β -sitosterol concentrations up to 30 mM, with different support particle sizes. Kinetic control of the biotransformation process becomes apparent for support particle sizes below 0.12–0.2 mm.

Abstract: Saccharomyces cerevisiae lacks most of the depolymerising enzymes required for efficient hydrolysis and utilisation of polysaccharide-rich biomass. To allow extracellular degradation of polysaccharides, genes encoding amylopullulanase (LKA1), pectate lyase (PEL5), polygalacturonase (PEH1), endo-β-1,4-D-glucanase (END1), cellobiohydrolase (CBH1), exo-β-1,3-D-glucanase (EXG1), cellobiase (β-glucosidase; BGL1) and endo-β-D-xylanase (XYN4) were introduced jointly into a laboratory strain of S. cerevisiae. These transformants were able to grow on starch, pectate, cellobiose and to some extent on cellulose (solka-floc and lichenan). These results pave the way for the development of one-step bioconversion processing of plant biomass in the fuel, animal feed, baking and beverage industries. © Rapid Science Ltd. 1998

Abstract: Hydroxamic acids (HA), with the general formula R–CO–NHOH, are chelating agents which may be used in a number of interesting applications, such as medicine and waste water treatment. In this paper, we describe the enzymatic synthesis of HA with various chain lengths (from C2 to C18), using three microbial enzymes. For short- and middle-chain HA synthesis, using amidases from Rhodococcus sp. R312, the optimal working pH was found to be pH 7 or 8, depending on the amide substrate used. Different Michaelis–Menten constants were also determined. For fatty HA synthesis, using lipase from Candida parapsilosis, the optimal working conditions were determined to be pH 6, 1 M hydroxylamine and 40°C. Because of the favorable bioconversion yields achieved, the enzymatic synthesis of HA with the appropriate biocatalysts appears to be an interesting alternative to chemical synthesis.

Abstract: The yeast Saccharomyces cerevisiae has been used to efficiently produce l-malic acid from fumaric acid. Fumarase is responsible for the reversible conversion of fumaric and l-malic acids in the TCA cycle. To investigate the function of mitochondrial and cytoplasmic fumarase iso-enzymes in l-malic acid bioconversion, a wild-type strain and a cytoplasmic respiratory-deficient mutant devoid of functional mitochondria were employed. The mutant strain, which only contained the cytoplasmic fumarase, was still functional in fumaric acid to l-malic acid bioconversion. However, its specific conversion rate was much lower (0.20 g/g·h) than that of the wild-type strain (0.55 g/g·h).

Abstract: Hairy roots of Brugmansia candida were used to bioconvert hydroquinone into arbutin. The highest bioconversion, with the lowest damage to the cells, was attained when concentrations of 20-40 mg/L hydroquinone were used. Sugars (sucrose, glucose, mannitol, and sorbitol) at concentrations of 30-120 g/L enhanced bioconversion, and, of these, sucrose was the most effective. Two different free-radical scavengers were also tested: sodium benzoate and gallic acid. The first one diminished biotransformation efficiency; gallic acid did not affect biotransformation at all. Preliminary permeabilization treatments tested failed to liberate arbutin into the medium, and provoked a total loss in cell viability.