Introduction. Cellular Growth Reactions. Analysis of Reaction Rates. Modelling of Reaction Kinetics. Morphologically Structured Models. Population Balances Based on Cell Number. Mass Transfer. Ideal Bioreactors. Bioreactor Modelling. Index.

Bioreaction Engineering Principles

Transgenic hairy roots: recent trends and applications

Pharmaceutically significant secondary metabolites or phytopharmaceuticals include alkaloids, glycosides, flavonoids, volatile oils, tannins, resins etc. Currently, most of these secondary metabolites are isolated from wild or cultivated plants because their chemical synthesis is either extremely difficult or economically infeasible. Biotechnological production in plant cell cultures is an attractive alternative, but to date this has had only limited commercial success because of a lack of understanding of how these metabolites are synthesized. Plants and/or plant cells in vitro, show physiological and morphological responses to microbial, physical or chemical factors which are known as ‘elicitors’. Elicitation is a process of induced or enhanced synthesis of secondary metabolites by the plants to ensure their survival, persistence and competitiveness. Here, we discuss the classification of elicitors, their mechanism of action, and applications for the production of phyto-pharmaceuticals from medicinal plants.

Plant cell elicitation for production of secondary metabolites: A review

A large number of studies have presented empirical arguments for the existence of alternative stable states (ASS) in a wide range of ecological systems. However, most of these studies have used non-manipulative, indirect methods, which findings remain open for alternative explanations. Here, we review the direct evidence for ASS resulting from manipulation experiments. We distinguish four conclusive experimental approaches which test for predictions made by the hysteresis effect: (1) discontinuity in the response to an environmental driving parameter, (2) lack of recovery potential after a perturbation, (3) divergence due to different initial conditions and (4) random divergence. Based on an extensive literature search we found 35 corresponding experiments. We assessed the ecological stability of the reported contrasting states using the minimum turnover of individuals in terms of life span and classified the studies according to 4 categories: (1) experimental system, (2) habitat type, (3) involved organisms and (4) theoretical framework. 13 experiments have directly demonstrated the existence of alternative stable states while 8 showed the absence of ASS in other cases. 14 experiments did not fulfil the requirements of a conclusive test, mostly because they applied a too short time scale. We found a bias towards laboratory experiments compared to field experiments in demonstrating bistability. There was no clear pattern of the distribution of ASS over categories. The absence of ASS in 38% of the tested systems indicates that ASS are just one possibility of how ecological systems can behave. The relevance of the concept of ASS for natural systems is discussed, in particular under consideration of the observed laboratory bias, perturbation frequency and variable environments. It is argued, that even for a permanently transient system, alternative attractors may still be of relevance.

Direct experimental evidence for alternative stable states: a review

Plant cell and organ cultures have emerged as potential sources of secondary metabolites, which are used as pharmaceuticals, agrochemicals, flavors, fragrances, coloring agents, biopesticides, and food additives. In recent years, various strategies have been developed to assess biomass accumulation and synthesis of secondary compounds in cultures. Biomass accumulation and metabolite biosynthesis are two-stage events, and the parameters that control the growth and multiplication of cultured cells/organs and biomass accumulation are controlled in the first stage. Parameters that assist with the biosynthesis of metabolites are controlled in the second stage. The selection of high-producing cells or organ clones; optimization of medium parameters such as suitable medium, salt, sugar, nitrogen, phosphate, and plant growth regulator levels; and physical factors such as temperature, illumination, light quality, medium pH, agitation, aeration, and environmental gas (e.g., oxygen, carbon dioxide, and ethylene) are controlled in the first stage of the culture process. Elicitation, replenishment of nutrient and precursor feeding, permeabilization, and immobilization strategies assist with the accumulation of metabolites and can be applied in the second stage of the culture process. By following stage-specific strategies, it is possible to produce large amounts of biomass with an increase in the accumulation of secondary compounds.

Production of secondary metabolites from cell and organ cultures: strategies and approaches for biomass improvement and metabolite accumulation

http://www.ecs.umass.edu/che/henson_group/research/bioreactor/ces00z.pdf

Martin A. Hjortso

Papers

Model predictive control of continuous yeast bioreactors using cell population balance models

Coupling pore-scale networks to continuum-scale models of porous media

A conceptual model of autonomous oscillations in microbial cultures

Population balance models of autonomous microbial oscillations

Statistical analysis of elicitation strategies for thiarubrine A production in hairy root cultures of Ambrosia artemisiifolia