Theoretical and methodological studies of continuous microbial bioreactors

Abstract

This article reviews most of the author's studies on process development and reactor design for continuous microbial reactions. (1) Enzyme reactions of growing and non-growing microbial cells immobilized in agar gel beads were analyzed pertaining to the effects of external and internal diffusion of substrate on reaction kinetics. (2) Experimental correlations of production rates of beta-fructosidase and acid phosphatase with dilution rate of continuous culture were simulated based on an operon model for enzyme regulation. (3) Population dynamics of an amylase-producing bacteria and their mutant were discussed in relation to enzyme productivity in a continuous culture of spore-forming bacteria. (4) Plasmid mobilization in a mixed population of donor, recipient, and helper cells was investigated in a continuous culture as a model study of accidental release of a genetically modified plasmid into a natural environment. (5) A production rate increase of up to 100-fold was achieved by cell-recycle culturing of continuous acetic acid fermentation using a filter module with a hollow fiber membrane. (6) The feasibility of a continuous surface culture for the biooxidation of organic substances was ascribed to an enhanced oxygen absorption rate in the presence of a microbial film on a liquid surface. (7) Simultaneous separation of inhibitory products using an electrodialysis module during some organic acid fermentations was effective for increasing production in a continuous culture.

A Small-Volume, Low-Cost, and Versatile Continuous Culture Device

“…Continuous culture conditions result in a stable and controllable set of physico-chemical conditions in which growth rate, pH, biomass, as well as the concentrations of dissolved oxygen, proteins, and metabolites reach a dynamic equilibrium and remain approximately constant over an extended period of time [ 3 , 9 , 14 , 15 ]. These highly-reproducible parameters contribute to the establishment of a physiological steady state in cell populations, which decreases variability in quantitative experiments such as RNA sequencing and mass spectrometry [ 14 – 17 ]. Systems biology that aims at analyzing and integrating large amounts of data to understand complex interactions between components of biological systems would thus particularly benefit from controlled and highly-reproducible growth parameters provided by continuous culture devices [ 14 , 18 ].…”

“…This is not surprising since commercially available continuous culture instruments are expensive, not designed to handle small volumes, rarely customizable, and can lack the flexibility required to accommodate a large diversity of experimental conditions. As a consequence, most studies are thus conducted using batch cultures, a simple, easy to implement, low cost, and highly scalable cultivation procedure that however results in a continuously fluctuating chemical environment [ 17 , 19 ]. Some laboratories have developed continuous culture instruments for their specific needs.…”

Continuous cultivation of photosynthetic bacteria for fatty acids production

“…However, there are many difficulties in maintaining a continuous culture for long periods without mutation and microbial 4 contamination. Population changes due to mutation or microbial contamination in the pure culture of a microbial strain have frequently been reported in continuous culture systems (Toda, 2003).…”

Cultivo contínuo de Streptococcus pneumoniae sorotipo 14: metabolismo e cinética de produção de polissacarídeo capsular.

“…Isto frequentemente resulta em dados complexos difíceis e até impossíveis de interpretar(HOSKISSON e HOBBS, 2005).A manutenção das células em um mesmo estado fisiológico torna o processo contínuo uma excelente ferramenta para estudos de mecanismos de regulação metabólica ou ainda, para estudos de melhoramento da composição de meio de cultura. Isto porque é possível observar a atividade do micro-organismo em diferentes ambientes controlados pelo investigador, mudando simplesmente a vazão específica de alimentação ou a composição do meio de alimentação(HOSKISSON e HOBBS, 2005;TODA, 2003).…”