The solvent-tolerant strain Pseudomonas putida DOT-T1E was grown in batch fermentations in a 5-liter bioreactor in the presence and absence of 10% (vol/vol) of the organic solvent 1-decanol. The growth behavior and cellular energetics, such as the cellular ATP content and the energy charge, as well as the cell surface hydrophobicity and charge, were measured in cells growing in the presence and absence of 1-decanol. Although the cells growing in the presence of 1-decanol showed an about 10% reduced growth rate and a 48% reduced growth yield, no significant differences were measured either in the ATP and potassium contents or in the energy charge, indicating that the cells adapted completely at the levels of membrane permeability and energetics. Although the bacteria needed additional energy for adaptation to the presence of the solvent, they were able to maintain or activate electron transport phosphorylation, allowing homeostasis of the ATP level and energy charge in the presence of the solvent, at the price of a reduced growth yield. On the other hand, significantly enhanced cell hydrophobicities and more negative cell surface charges were observed in cells grown in the presence of 1-decanol. Both reactions occurred within about 10 min after the addition of the solvent and were significantly different after killing of the cells with toxic concentrations of HgCl 2 . This adaptation of the surface properties of the bacterium to the presence of solvents seems to be very similar to previously observed reactions on the level of lipopolysaccharides, with which bacteria adapt to environmental stresses, such as heat shock, antibiotics, or low oxygen content. The results give clear physiological indications that the process with P. putida DOT-T1E as the biocatalyst and 1-decanol as the solvent is a stable system for two-phase biotransformations that will allow the production of fine chemicals in economically sound amounts.
The reactor systems used for microbial electrosynthesis, i.e. bioelectrochemical systems for achieving bioproduction so far reported in literature are relatively small in scale and highly diverse in their architecture and modes of operation. The often diverging requirements of the electrochemical and the biological processes and the interdisciplinarity of the field make the engineering of these systems a special challenge. This has led to multiple, differently optimized approaches of reactor vessels, designs and operating conditions making standardization and normalization or even a systematic engineering almost impossible. Overcoming this lack of standardization, scalability and knowledge‐driven engineering is the driving force for this work introducing an upgrade kit for bioreactors transforming these reversibly to bioelectroreactors. The prototypes of the bioreactor upgrade kit were integrated with commercial bioreactor (fermentor) systems and performances compared to a classic, small‐scale bioelectrochemical glass cell system. The use of the upgrade kit allowed interfacing with the existing infrastructure of the conventional bioreactors for growing electroactive microorganisms in pure culture conditions, with the added electrochemical control and further process monitoring. The results of growing Shewanella oneidensis MR‐1 clearly show that these systems can be used to control, monitor, and scale microbial bioelectrochemical processes, providing better resolution of the data for the tested experimental conditions.
Microbial electrosynthesis (MES) is an exciting and dynamic research area at the nexus of microbiology and electrochemistry. To pave the way of MES to application, reactor infrastructure is needed that meets the requirements of both biological, and electrochemical engineering. Recently we presented an upgrade kit facilitating turning commercial bioreactors based on batch stirred tank reactors (BSTR) into electrobioreactors that can be scaled and benchmarked. The upgrade kit comprises electrodes and an inlay with membrane, separating the BSTR chamber into anode and cathode compartments. The obtained electrobioreactors enable seizing the existing infrastructure for monitoring and controlling the bioprocess while being complemented by electrochemical control and measurement. Here the effect of the upgrade kit on mass transfer was investigated in a 1 L electrobioreactor using experimental approaches and modeling of fluid dynamics. It is shown that the fluid dynamics in the BSTR are changed dramatically, impacting the integral parameters volumetric mass transfer coefficient, k L a, and mixing time, θ. The influences of the inlay chamber and electrodes as well as stirrer position and geometry are described. Additionally, the sterilizability of the inlay, housing the polymer-based membrane of the electrobioreactor, which is needed for operating two-chamber MES based on microbial pure cultures, are demonstrated.
Primary microbial electrochemical technologies are utilizing the interfacing of microbial redox reactions and electrodes. Based on its exploitation as recognition element for bioelectrochemical glucose sensors and inspired by its biotechnological potential Gluconobacter oxydans was studied on its suitability for microbial electrosynthesis. It is demonstrated that in bioelectroreactors the conversion of glucose by G. oxydans based on mediated extracellular electron transfer is not related to electric current flow. Oxidation current can only be recorded after preceding aeration phase, but the response does strongly depend on the microbial activity status, pO2 and gas supply as well as the pH regime. It is proven that the electric current is derived from the microbial cells, but the mechanism still needs to be elucidated. The suitability of G. oxydans for microbial electrosynthesis but also for bioelectrochemical sensors is critically assessed.
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