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There is considerable interest in exploiting the novel physical and biological properties of microbial exopolysaccharides in industry and medicine. For economic and scientific reasons, large scale production under carefully monitored and controlled conditions is required. Producing exopolysaccharides in industrial fermenters poses several complex bioengineering and microbiological challenges relating primarily to the very high viscosities of such culture media, which are often exacerbated by the producing organism's morphology. What these problems are, and the strategies for dealing with them are discussed critically in this review, using pullulan, curdlan, xanthan, and fungal β-glucans as examples of industrially produced microbial exopolysaccharides. The role of fermenter configuration in their production is also examined.

Many of the foods we eat are of microbial origin or contain constituents produced by microbial fermentation. This chapter considers the biotechnological problems associated with growing these producing strains, most of which are aerobic organisms, in large scale fermenters. It discusses how rational fermenter design is a crucial component in providing them with the physical environment for optimal desirable metabolite production, which with the filamentous fungi is often related to their morphological form. It also discusses how some of the problems in achieving this can be ameliorated by innovative fermenter configuration. Carefully selected examples are used to illustrate the practical application on an industrial scale of these philosophies and suggestions are made about how fermentation technology is likely to change in the future to satisfy the increasing demands for highly nutritious and safe foods for human consumption.

Publisher Summary This chapter evaluates recent advances in submerged liquid cultivation of the vegetative or mycelial forms of those members of the “higher fungi” that produce macroscopic spore-bearing structures, namely the macrofungi. The chapter focuses on those producing potentially useful natural products and novel compounds with interesting biological activities by means of submerged culture fermentation processes. The taxonomy of the fungi is in a state of rapid flux arising from the widespread use of molecular genetics to characterize and classify the organisms, and many of earlier ideas on their phylogenetic relationships must be revised. Fungi can be defined as being eukaryotic, characteristically mycelial organisms, with chitin-based cell walls, an absorptive nutrition, and which reproduce by production of spores. Some of the macrofungi are edible, and some also have biotechnological and environmental applications. Edible macrofungi have long been consumed both as valuable protein and energy sources, and also for improving human health and longevity.

Background: Novel analytical tools, which shorten the long and costly development cycles of biopharmaceuticals are essential. Metabolic flux analysis (MFA) shows great promise in improving our understanding of the metabolism of cell factories in bioreactors, but currently only provides information post-process using conventional off-line methods. MFA combined with real time multianalyte process monitoring techniques provides a valuable platform technology allowing real time insights into metabolic responses of cell factories in bioreactors. This could have a major impact in the bioprocessing industry, ultimately improving product consistency, productivity and shortening development cycles. Results: This is the first investigation using Near Infrared Spectroscopy (NIRS) in situ combined with metabolic flux modelling which is both a significant challenge and considerable extension of these techniques. We investigated the feasibility of our approach using the industrial workhorse Pichia pastoris in a simplified model system. A parental P. pastoris strain (i.e. which does not synthesize recombinant protein) was used to allow definition of distinct metabolic states focusing solely upon the prediction of intracellular fluxes in central carbon metabolism. Extracellular fluxes were determined using off-line conventional reference methods and on-line NIR predictions (calculated by multivariate analysis using the partial least squares algorithm, PLS). The results showed that the PLS-NIRS models for biomass and glycerol were accurate: correlation coefficients, R 2 , above 0.90 and the root mean square error of prediction, RMSEP, of 1.17 and 2.90 g/L, respectively. The analytical quality of the NIR models was demonstrated by direct comparison with the standard error of the laboratory (SEL), which showed that performance of the NIR models was suitable for quantifying biomass and glycerol for calculating extracellular metabolite rates and used as independent inputs for the MFA (RMSEP lower than 1.5 × SEL). Furthermore, the results for the MFA from both datasets passed consistency tests performed for each steady state, showing that the precision of on-line NIRS is equivalent to that obtained by the off-line measurements. Conclusions: The findings of this study show for the first time the potential of NIRS as an input generating for MFA models, contributing to the optimization of cell factory metabolism in real-time.