Eco-Efficiency Analysis of biotechnological processes

For almost 50 years now, biotechnological production processes have been used for industrial production of amino acids. Market development has been particularly dynamic for the flavor-enhancer glutamate and the animal feed amino acids l-lysine, l-threonine, and l-tryptophan, which are produced by fermentation processes using high-performance strains of Corynebacterium glutamicum and Escherichia coli from sugar sources such as molasses, sucrose, or glucose. But the market for amino acids in synthesis is also becoming increasingly important, with annual growth rates of 5–7%. The use of enzymes and whole cell biocatalysts has proven particularly valuable in production of both proteinogenic and nonproteinogenic l-amino acids, d-amino acids, and enantiomerically pure amino acid derivatives, which are of great interest as building blocks for active ingredients that are applied as pharmaceuticals, cosmetics, and agricultural products. Nutrition and health will continue to be the driving forces for exploiting the potential of microorganisms, and possibly also of suitable plants, to arrive at even more efficient processes for amino acid production.     

Microbial biofilms in biotechnological processes

This review summarizes the information concerning the following applications of microbial biofilms in biotechnology: the biodegradation of organic substances and other contaminants during wastewater treatment, biosynthesis, and biocatalysis. The main types of reactors for implementing biotechnical processes based on microbial biofilms are discussed. The advantages and drawbacks of biocatalysts in the form of microbial biofilms for the biotransformation of organic substances are examined.     

Optimization of nonlinear biotechnological processes with linear programming: Application to citric acid production by Aspergillus niger

The metabolic pathway and the properties of many of the enzymes involved in the citric acid biosynthesis in the mold Aspergillus niger are well known. This fact, together with the availability of new theoretical frameworks aimed at quantitative analyses of control and dynamics in metabolic systems, has allowed us to construct a mathematical model of the carbohydrate metabolism in Aspergillus niger under conditions of citric acid accumulation. The model makes use of the S-system representation of biochemical systems, which renders it possible to use linear programming to optimize the process. It was found that maintaining the metabolite pools within narrow physiological limits (20% around the basal steady-state level) and allowing the enzyme concentrations to vary within a range of 0.1 to 50 times their basal values it is possible to triple the glycolytic flux while maintaining 100% yield of substrate transformation. To achieve these improvements it is necessary to modulate seven or more enzymes simultaneously. Although this seems difficult to implement at present, the results are useful because they indicate what the theoretical limits are and because they suggest several alternative strategies. (c) 1996 John Wiley & Sons, Inc.     

LFT models of continuous biotechnological processes

The aim of the paper is to obtain suitable state-space models of continuous biotechnological processes (CBTP) in the framework of Linear Fractional Transformation (LFT). The LFT models are starting point in most of the advanced robust control design and analysis methods. Therefore, a linearized process model in the state-space is used whose elements are supposed to vary within certain bounds to represent the nonlinear behaviour of the real plant. The performance specifications are defined in the frequency domain through weighting functions. Two LFT models of CBTP are obtained ready for controller design aimed to optimize robust stability margins and robust performance, respectively.     

Microbial, enzymatic, and immune biosensors for ecological monitoring and control of biotechnological processes

Results of the research performed at the Institute of Biochemistry and Physiology of Microorganisms, Russian Academy of Sciences, on designing immunobiosensors for detection of toxic compounds and microbial cells enzyme-based biosensors for detection of hydrocarbons and alcohols, and microbial biosensors for aromatic compounds, surfactants, and biological oxygen consumption are briefed. Parameters of the mediator electrodes involving microbial cells and data on the properties of microbial biofuel cells--devices based on biosensor principle and representing alternative sources of electric energy--are given.     

Tubular membrane bioreactors for biotechnological processes

This article is an overview of bioreactors using tubular membranes such as hollow fibers or ceramic capillaries for cultivation processes. This diverse group of bioreactor is described here in regard to the membrane materials used, operational modes, and configurations. The typical advantages of this kind of system such as environments with low shear stress together with high cell densities and also disadvantages like poor oxygen supply are summed up. As the usage of tubular membrane bioreactors is not restricted to a certain organism, a brief overview of various applications covering nearly all types of cells from prokaryotic to eukaryotic cells is also given here.     

The biotechnological production of sorbitol

Sorbitol, a polyol found in many fruits, is of increasing industrial interest as a sweetener, humectant, texturizer and softener. At present, it is produced chemically. The bacterium Zymomonas mobilis is able to produce sorbitol and gluconic acid from fructose and glucose, respectively. This is possible in a one-step reaction via a glucose-fructose oxidoreductase so far only known from Z. mobilis. The possibilities for the industrial production of sorbitol by Z. mobilis are discussed, and compared with the current chemical production method as well as other microbiological processes. Electronic Publication     

Catabolism of hydroxyacids and biotechnological production of lactones by Yarrowia lipolytica

The gamma- and delta-lactones of less than 12 carbons constitute a group of compounds of great interest to the flavour industry. It is possible to produce some of these lactones through biotechnology. For instance, gamma-decalactone can be obtained by biotransformation of methyl ricinoleate. Among the organisms used for this bioproduction, Yarrowia lipolytica is a yeast of choice. It is well adapted to growth on hydrophobic substrates, thanks to its efficient and numerous lipases, cytochrome P450, acyl-CoA oxidases and its ability to produce biosurfactants. Furthermore, genetic tools have been developed for its study. This review deals with the production of lactones by Y. lipolytica with special emphasis on the biotransformation of methyl ricinoleate to gamma-decalactone. When appropriate, information from the lipid metabolism of other yeast species is presented.     

Carbamoylases: characteristics and applications in biotechnological processes

Enzymatic kinetic resolution is a widely used biotechnological tool for the production of enantiomerically pure/enriched compounds. This technique takes advantage of the enantioselectivity or enantiospecificity of an enzyme for one of the enantiomers of a racemic substrate to isolate the desired isomer. N-Carbamoyl-d- and l-amino acid amidohydrolases (d- and l-carbamoylases) are model enzymes for this procedure due to their strict enantiospecificity. Carbamoylase-based kinetic resolution of amino acids has been applied for the last three decades, allowing the production of optically pure d- or l-amino acids. Furthermore, this enzyme has become crucial in the industrially used multienzymatic system known as “Hydantoinase Process,” where the kinetic resolution produced by coupling an enantioselective hydantoinase and the enantiospecific carbamoylase is enhanced by the enzymatic/chemical dynamic kinetic resolution of the low-rate hydrolyzed substrate. This review outlines the properties of d- and l-carbamoylases, emphasizing their biochemical/structural characteristics and their biotechnological applications. It also pinpoints new applications for the exploitation of carbamoylases over the forthcoming years.     

Applications of yeast flocculation in biotechnological processes

A review on the main aspects associated with yeast flocculation and its application in biotechnological processes is presented. This subject is addressed following three main aspects—the basics of yeast flocculation, the development of “new” flocculating yeast strains and bioreactor development. In what concerns the basics of yeast flocculation, the state of the art on the most relevant aspects of mechanism, physiology and genetics of yeast flocculation is reported. The construction of flocculating yeast strains includes not only the recombinant constitutive flocculent brewer's yeast, but also recombinant flocculent yeast for lactose metabolisation and ethanol production. Furthermore, recent work on the heterologous β-galactosidase production using a recombinant flocculentSaccharomyces cerevisiae is considered. As bioreactors using flocculating yeast cells have particular properties, mainly associated with a high solid phase hold-up, a section dedicated to its operation is presented. Aspects such as bioreactor productivity and culture stability as well as bioreactor hydrodynamics and mass transfer properties of flocculating cell cultures are considered. Finally, the paper concludes describing some of the applications of high cell density flocculation bioreactors and discussing potential new uses of these systems.     

The main hygienic aspects of biotechnological processes

It was shown that the present technologies and implementation at the majority of biotechnological plants do not completely meet the hygienic requirements. Under such conditions, there is a complex of unfavourable factors which can have a negative effect on the production areas and environment and consequently on the workers and nearby population. The biological and, at some plants, chemical factors are the leading in the complex. The main aspects of the studies aimed at increasing the safety of biotechnological production, improving the labor conditions and decreasing the disease incidence in the personnel are described in general.     

Metabolic pathways and biotechnological production of l-cysteine

l-Cysteine is an important amino acid both biologically and commercially. Although most amino acids are commercially produced by fermentation, cysteine is mainly produced by protein hydrolysis. However, synthetic or biotechnological products have been preferred in the market. Biotechnological processes for cysteine production, both enzymatic and fermentative processes, are discussed. Enzymatic process, the asymmetric hydrolysis of dl-2-amino-Δ²-thiazoline-4-carboxylic acid to l-cysteine, has been developed and industrialized. The l-cysteine biosynthetic pathways of Escherichia coli and Corynebacterium glutamicum, which are used in many amino acid production processes, are also described. These two bacteria have basically same l-cysteine biosynthetic pathways. l-Cysteine-degrading enzymes and l-cysteine-exporting proteins both in E. coli and C. glutamicum are also described. In conclusion, for the effective fermentative production of l-cysteine directly from glucose, the combination of enhancing biosynthetic activity, weakening the degradation pathway, and exploiting the export system seems to be effective.     

Biosynthesis and biotechnological production of serotonin derivatives

Serotonin derivatives belong to a class of phenylpropanoid amides found at low levels in a wide range of plant species. Representative serotonin derivatives include feruloylserotonin (FS) and 4-coumaroylserotonin (CS). Since the first identification of serotonin derivatives in safflower seeds, their occurrence, biological significance, and pharmacological properties have been reported. Recently, serotonin N-hydroxycinnamoyl transferase (SHT), which is responsible for the synthesis of serotonin derivatives, was cloned from pepper (Capsicum annuum) and characterized in terms of its enzyme kinetics. Using the SHT gene, many attempts have been made to either increase the level of serotonin derivatives in transgenic plants or produce serotonin derivatives de novo in microbes by dual expression of key genes such as SHT and 4-coumarate-CoA ligase (4CL). Due to the strong antioxidant activity and other therapeutic properties of serotonin derivatives, these compounds may have high potential in treatment and prophylaxis, as cosmetic ingredients, and as major components of functional foods or feeds that have health-improving effects. This review examines the biosynthesis of serotonin derivatives, corresponding enzymes, heterologous production in plants or microbes, and their applications.     

A self-tuning vision system for monitoring biotechnological processes: I. Application to production of pullulan by Aureobasidium pullulans

A prototype of a self-tuning vision system (STVS) has been developed to monitor cell population in fermentations. The STVS combines classical image processing techniques, neural networks and fuzzy logic technologies. By combining these technologies the STVS is able to analyze sampled images of the culture. The proposed system can be "tailored" with minimum effort by an expert who can "teach" the system to recognize cells by showing examples of different morphologies. After adaptation, the STVS is able to capture images, isolate the different cells, classify them according to the expert's criteria, and provide the profile of the cell's population. The system was applied to the classification and analysis of Aureobasidium pullulans. The importance of understanding the changes of population distribution during the fermentation and its effect in the production of pullulan are emphasized. The STVS can be used for monitoring and control of the cell population in small research fermentors or in large-scale production.     

Metabolic effects of furaldehydes and impacts on biotechnological processes

There is a growing awareness that lignocellulose will be a major raw material for production of both fuel and chemicals in the coming decades—most likely through various fermentation routes. Considerable attention has been given to the problem of finding efficient means of separating the major constituents in lignocellulose (i.e., lignin, hemicellulose, and cellulose) and to efficiently hydrolyze the carbohydrate parts into sugars. In these processes, by-products will inevitably form to some extent, and these will have to be dealt with in the ensuing microbial processes. One group of compounds in this category is the furaldehydes. 2-Furaldehyde (furfural) and substituted 2-furaldehydes—most importantly 5-hydroxymethyl-2-furaldehyde—are the dominant inhibitory compounds found in lignocellulosic hydrolyzates. The furaldehydes are known to have biological effects and act as inhibitors in fermentation processes. The effects of these compounds will therefore have to be considered in the design of biotechnological processes using lignocellulose. In this short review, we take a look at known metabolic effects, as well as strategies to overcome problems in biotechnological applications caused by furaldehydes.