PETR: A novel peristaltic mixed tubular bioreactor simulating human colonic conditions.

A novel bioreactor simulating human colonic conditions for in vitro cultivation of intestinal microbiota is presented. The PEristaltic mixed Tubular bioReactor (PETR) is modular designed and periodically kneaded to simulate intestinal peristalsis. The reactor is introduced, characterized from a bioprocess engineer's perspective and discussed in its ability to mimic colon conditions. PETR provides physiological temperature and appropriate anaerobic conditions, simulates intestinal peristalsis, and has a mean residence time of 32.8 ± 0.8 h comparable to the adult human colon. The single-tube design enables a time-constant and longitudinally progressive pH gradient from 5.5 to 7.0. Using a dialysis liquid containing high molecular weight polyethylene glycol, the integrated dialysis system efficiently absorbs short chain fatty acids (up to 60%) and water (on average 850 mL d-1 ). Cultivation of a typical gut bacterium (Bifidobacterium animalis) was performed to demonstrate the applicability for controlled microbiota cultivation. PETR is unique in combining simulation of the entire colon, peristaltic mixing, dialytic water and metabolite absorption, and a progressive pH gradient in a single-tube design. PETR is a further step to precise replication of colonic conditions in vitro for reliable and reproducible microbiota research, such as studying the effect of food compounds, prebiotics or probiotics, or the development and treatment of infections with enteric pathogens, but also for further medical applications such as drug delivery studies or to study the effect of drugs on and their degradation by the microbiota.

3D-printed micro bubble column reactor with integrated microsensors for biotechnological applications: From design to evaluation.

With the technological advances in 3D printing technology, which are associated with ever-increasing printing resolution, additive manufacturing is now increasingly being used for rapid manufacturing of complex devices including microsystems development for laboratory applications. Personalized experimental devices or entire bioreactors of high complexity can be manufactured within few hours from start to finish. This study presents a customized 3D-printed micro bubble column reactor (3D-µBCR), which can be used for the cultivation of microorganisms (e.g., Saccharomyces cerevisiae) and allows online-monitoring of process parameters through integrated microsensor technology. The modular 3D-µBCR achieves rapid homogenization in less than 1 s and high oxygen transfer with kLa values up to 788 h-1 and is able to monitor biomass, pH, and DOT in the fluid phase, as well as CO2 and O2 in the gas phase. By extensive comparison of different reactor designs, the influence of the geometry on the resulting hydrodynamics was investigated. In order to quantify local flow patterns in the fluid, a three-dimensional and transient multiphase Computational Fluid Dynamics model was successfully developed and applied. The presented 3D-µBCR shows enormous potential for experimental parallelization and enables a high level of flexibility in reactor design, which can support versatile process development.

Quantification of microaerobic growth of Geobacter sulfurreducens.

Geobacter sulfurreducens was originally considered a strict anaerobe. However, this bacterium was later shown to not only tolerate exposure to oxygen but also to use it as terminal electron acceptor. Research performed has so far only revealed the general ability of G. sulfurreducens to reduce oxygen, but the oxygen uptake rate has not been quantified yet, nor has evidence been provided as to how the bacterium achieves oxygen reduction. Therefore, microaerobic growth of G. sulfurreducens was investigated here with better defined operating conditions as previously performed and a transcriptome analysis was performed to elucidate possible metabolic mechanisms important for oxygen reduction in G. sulfurreducens. The investigations revealed that cell growth with oxygen is possible to the same extent as with fumarate if the maximum specific oxygen uptake rate (sOUR) of 95 mgO2 gCDW-1 h-1 is not surpassed. Hereby, the entire amount of introduced oxygen is reduced. When oxygen concentrations are too high, cell growth is completely inhibited and there is no partial oxygen consumption. Transcriptome analysis suggests a menaquinol oxidase to be the enzyme responsible for oxygen reduction. Transcriptome analysis has further revealed three different survival strategies, depending on the oxygen concentration present. When prompted with small amounts of oxygen, G. sulfurreducens will try to escape the microaerobic area; if oxygen concentrations are higher, cells will focus on rapid and complete oxygen reduction coupled to cell growth; and ultimately cells will form protective layers if a complete reduction becomes impossible. The results presented here have important implications for understanding how G. sulfurreducens survives exposure to oxygen.

Novel electrodynamic oscillation technique enables enhanced mass transfer and mixing for cultivation in micro-bioreactor.

Micro-bioreactors (MBRs) have become an indispensable part for modern bioprocess development enabling automated experiments in parallel while reducing material cost. Novel developments aim to further intensify the advantages as dimensions are being reduced. However, one factor hindering the scale-down of cultivation systems is to provide adequate mixing and mass transfer. Here, vertical oscillation is demonstrated as an effective method for mixing of MBRs with a reaction volume of 20 µL providing adequate mass transfer. Electrodynamic exciters are used to transduce kinetic energy onto the cultivation broth avoiding additional moving parts inside the applied model MBR. The induced vertical vibration leads to oscillation of the liquid surface corresponding to the frequency and displacement. On this basis, the resonance frequency of the fluid was identified as the most decisive factor for mixing performance. Applying this vertical oscillation method outstanding mixing times below 1 s and exceptionally high oxygen transport with volumetric mass transfer coefficients (kL a) above 1,000/hr can be successfully achieved and controlled. To evaluate the applicability of this vertical oscillation mixing for low volume MBR systems, cultivations of Escherichia coli BL21 as proof-of-concept were performed. The dissolved oxygen was successfully online monitored to assure any avoidance of oxygen limitations during the cultivation. The here presented data illustrate the high potential of the vertical oscillation technique as a flexible measure to adapt mixing times and oxygen transfer according to experimental demands. Thus, the mixing technique is a promising tool for various biological and chemical micro-scale applications still enabling adequate mass transfer.