Activity Regeneration in Continuous Clostridium acetobutylicum Bioconversions of Glucose

Abstract

The regeneration of product‐forming activity by periodic nutrient feeding was studied in a continuous immobilized Clostridium acetobutylicum reactor system. Activity levels were increased by feeding ammonia and vitamins during selected intervals of the experiments; these compounds were not otherwise present in the medium. In contrast with experiments utilizing rich, complex media, regeneration with a defined medium resulted in increased rates of product formation far in excess of rates of concomitant cell growth. During one nutrient feeding phase, the increase in the butyric acid production rate was five times that of the cell growth‐rate increase, while the analogous ratio for butanol was 18. A hypothesis explaining the patterns of substrate consumption and product formation during the regeneration and deactivation periods has been developed: decreasing levels of exogenous ammonia induce the high‐affinity ammonia uptake system, causing the adenylate energy charge of the cells to increase; this in turn leads to the repression of glucose carbon flow through the EMP pathway and to the use of the acid‐forming catabolic reactions for more efficient production of ATP. Pulsewise addition of three different vitamins during one regeneration phase yielded interesting results, including a 50 % increase in butyric acid production rate that appeared to be connected with the addition of biotin. Finally, enumeration of the different morphological types of immobilized cells provided the first measurements of population dynamics in an immobilized cell system. Changes in the numbers of each cell type are consistent with the sporulation and germination processes of C. acetobutylicum observed with suspended cells.

Northern, Morphological, and Fermentation Analysis of spo0A Inactivation and Overexpression in Clostridium acetobutylicum ATCC 824

“…3). In contrast, strains 824(pMSPOA) and 824(pIMP1) produced solvents at lower rates but for a prolonged time, even after 70 h. It has been documented that the swollen clostridial forms of the cells are the active producers of solvents (spores and forespore-forming cells do not produce solvents) (16,29). Thus, these fermentation data should be interpreted as mean values from a mixed population of solvent-producing and nonsolvent-producing cells, with the fraction of these two types of cells varying substantially (as revealed by the morphological studies described above) among strains 824, 824(pMSPOA), and 824(pIMP1).…”

“…5C). However, these results should be reinterpreted on the basis of the actual fraction of cells producing solvents, i.e., cells in the clostridial form versus nonproducing forespore-forming cells and spores (16,29). In view of the fact that 824(pMSPOA) [and, to a lesser extent, 824(pIMP1)] contain a much larger fraction [by at least 50% for strain 824(pM-SPOA)] of forespore-forming cells and spores than does the parental strain, the fermentation data suggest that the ability of clostridial-form cells of strain 824(pMSPOA) to produce solvents is as great as and likely greater than that of those of the parental strain.…”

Predictor–Response Analysis of Fiber Optic Enzymatic Biosensors Constructed with Nonmodified E. coli BL21 (DE3) pGELAF+ Sensing 1,2-Dichloroethane

“…Reardon et al [16,18] have reviewed photoluminescence-based biosensor technology specific to environmental applications, and early research by Reardon et al [17] and Reardon and Bailey [15] reinforced the importance of identifying the metabolic state of cells during immobilization. Building on methods to support concerted and sustained biocatalysis immobilization has been a focus [11].…”