Microbial Cell Cultivations

R. I. Amann, W. Ludwig, and K. H. Schleifer, Phlogenetic identification and in situ detection of individual microbial-cells without cultivation, Microbiol Rev. 59 143 (1995). 

PHAs are usually accumulated within microbial cells when growth is limited by the depletion of nutrients such as nitrogen, oxygen, and other essential elements but have an excess of carbon source. Therefore, two-step cultivation is applied, whereby... 

Complex product mixtures In cases of cell cultivation (microbial, animal, or plant), multiple enzyme reactions are occurring in sequence or in parallel, the final product mixture contains cell mass, many metabolic by-products, and a remnant of the original nutrients. The cell mass also contains various cell components. 

You need to cultivate hypothetical microbial cells with the Monod kinetic parameter values of ymax = 5.0 hr-1 and Ks = 20 g/L. The cell yield (Yx/S) is 0.4 and the substrate concentration is 30 g/L. The required substrate conversion is 97%. Estimate the residence time required for the following fermenter configurations... 

H. Schleifer, Phylogenetic identification and in-situ detection of individual microbial cells without cultivation,... 

The different operation modes used in microbial fermentations are employed also in animal cell cultivation. Although many different classifications can be adopted, the most general is the one that considers the following operation modes batch, fed-batch, continuous, and perfusion, which is a continuous mode with cell recycle/retention (Castilho and Medronho, 2002). 

Although simple, the use of bubble aeration in animal cell cultivation requires the solution of certain technological challenges for its implementation, since one of the most characteristic features of animal cells is their low resistance to mechanical stresses. Cell membranes have a mechanical resistance that is much lower than that of microbial cell walls. According to Castilho and Anspach (2003), shear stresses in the order of 60 Pa are critical for cell death. 

Joshi JB, Elias CB, Patole MS (1996), Role of hydrodynamic shear in the cultivation of animal, plant and microbial cells, Chem. Eng. J. 62 121-141. 

In this review, it is described how the electronic noses are applied to on-line bioreactor monitoring for meeting the requirement of non-invasive real-time measurement and facilitating rapid and safe data generation from microbial and cell cultivations. 

Despite the enormous efforts in the biotechnological production of plant secondary metabolites, only three commercial processes have so far been implemented and no genetically modified plant is currently cultivated for the production of secondary metabolites. On the other hand, continuous and rapid advances in plant genomics, transcriptomics and proteomics could make the production of plant natural products by cell culture, transgenic plants or transfected microbial cells much more relevant in the future. 

Amann RI, Ludwig W, Schleifer KH (1995) Phylogenetic Identification and In Situ Detection of Individual Microbial Cells Without Cultivation. Microbiol Rev 59 143... 

The present review deals with the characterization of model protein foams and foams of various cultivation media. The suppression of foaming by antifoam agents and their effect on the oxygen transfer rate, microbial cell growth and product formation are discussed. The influence of process variables on the recovery of proteins by flotation without and with surfactants and mathematical models for protein flotation are presented. The effect of cultivation conditions, flotation equipment and operational parameters on foam flotation of microorganisms is reviewed. Floatable and non-floatable microorganisms are characterized by their surface envelope properties. A mathematical model for cell recovery by flotation is presented. Possible application areas of cell recovery by flotation are discussed. 

Centrifugal separators are applied in industry for the recovery of microbial cells from cultivation media. In waste water engineering a combination of flocculation and sedimentation is practiced. In the laboratory, cross-flow membrane separation is often used for retention of the cells. Some microorganisms and cells are enriched in the foam therefore, flotation is suited for the recovery of particular microbial cells from cultivation medium. 

Systematic investigations of microbial cell recovery by foam flotation were performed by Hansenula polymorpha [113-117] and Saccharomyces cerevisiae [ 118 -123] in continuous operation. The equipment used for flotation was often identical to that used for protein flotation. The microorganisms were cultivated in laboratory reactors on synthetic media in the absence of antifoam agents in continuous operation and the cell-containing cultivation medium was collected in a buffer storage and was fed into the middle of the colunm, at the top of the interface between the bubble and the foam layers. The height of the interface was controlled by an overflow. The foam left the colunm at the top. The cells were recovered from the foam liquid by a mechanical foam destroyer. The liquid residue left the column through an overflow [113] (Fig. 6). 

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