Microorganism immobilization

Enzyme electrodes belong to the family of biosensors. These also include systems with tissue sections or immobilized microorganism suspensions playing an analogous role as immobilized enzyme layers in enzyme electrodes. While the stability of enzyme electrode systems is the most difficult problem connected with their practical application, this is still more true with the bacteria and tissue electrodes. 

A collective anaerobic and aerobic treatment by immobilized microorganisms was first shown [66, 67] using calcium-alginate-immobilized co-cultures of a facultative anaerobic strain of Enterobacter cloacae. Reaction actually took place in the middle of the alginate beads. In these experiments, the reduced derivatives were oxidized in the outer parts of the alginate beads by a second aerobic strain (two different Alcaligenes species), which had the ability to oxidize 4-chloro-2-aminophenol. 

Chen KC, Chen JJ, Houng JY (2000) Improvement of nitrogen removal efficiency using immobilized microorganisms with oxidation-reduction potential monitoring. J Ind Microbiol Biotechnol 25 229-234... 

Chen K-C, Wu J-Y, Huang CC (2003) Decolorization of azo-dye using PVA-immobilized microorganism. J Biotechnol 101 241-252... 

P. C. Hallenbeck (1983) Immobilized microorganisms for hydrogen and ammonia production. Enzyme Microb. Technol., S 171-180... 

W. Muller, G. Wehnert, and T. Scheper, Fluorescence monitoring of immobilized microorganisms in cultures, Analytica Chim. Acta 213, 47-53 (1988). 

Microbial sensors usually possess long lifetimes, yet proper maintenance is mandatory. Thus, the overall activity of immobilized microorganisms should be kept as constant as possible. For this purpose, sensors should be stored in phosphate buffer containing no nutrients at 4°C in order to avoid microorganism growth in the membrane. If the sensor activity diminishes for some reason, then the sensor should be dipped into a nutrient medium... 

Analyte Immobilized microorganism Device type Response time (min) Range (mg/L)... 

Table 3.2 lists the most salient microbial sensors reported to date, together with the type of immobilized microorganism and measurement used, and the response time and dynamic range achieved in each instance. As can be seen, most of these biosensors rely on amperometric measurements. Some of them are described in detail below. 

Karube et al. have constructed several gas-sensing devices by using immobilized microorganisms and a potentiometric transducer. Two of them... 

The response to organic compounds depends on the assimilability by the immobilized microorganisms. Trichosporon brassicae, utilized propionic acid, n-butyric acid and ethanol. The measurement can be within 4 min using a flow cell (8). 

Biosensors have great advantages over spectrophotometric methods in the relatively little time consumed, ease of operation, and relatively low cost. Sensors using immobilized microorganisms instead of enzymes are being developed for environmental analysis. 

S. Takamatsu, I. Umemura, K. Yamamoto, T. Sato, T. Tosa, and 1. Chibata, Production of L-alanine from ammonium fumaiate using two immobilized microorganisms, Eur. /. Appl. Microbiol. Biotechnd., 15 147 (1982). 

Tubular fluidized and fixed bed fermenters are deviations from the simple bubble column fermenter. Often utilized in producing beer and ciders, these fermenters contain immobilized microorganisms or microbial films on support surfaces. Microbes lost with the product are continuously replenished by adding fresh microorganisms into the packed bed fermenters. In the fixed bed case, slow downward flow of the medium significantly reduces the shear removal (mobilization) of the microbes from the support materials and increases the residence time in the packed column. This is a typical characteristic of the trickle bed fermenter for continuous operation. Readers are referred to the packed bed reactor entry in this volume for a more... 

Laroche, C. and Gervais, R Unexpected thermal destruction of dried, glass bead-immobilized microorganisms as a function of water activity, Appl. Environ. 

Immobilized microorganisms and enzymes are becoming commercially available. One example is co-immobilized yeast and glucoamylase (Gist Brocades NV), which is used to simultaneously saccharify starch dextrins into glucose and ferment this to ethanol in fluidized bed reactors. 

Denitrification and Removal of Heavy Metals from Waste Water by Immobilized Microorganisms... 

For similar reasons as mentioned in denitrification, immobilized microorganisms would have advantages over suspended cultures in containing accumulated metals. In some cases, as it will be shown below, heavy metal uptake and some other microbiological functions, such as denitrification, can be performed in one operation, using the same fixed-bed bloreactor. 

As more and more sophisticated systems were studied the demands placed on the immobilized enzyme preparation constantly increased. The low stability of intracellular enzymes as well as the problems encountered in coenzyme regeneration accelerated the development of immobilized microorganisms or organelles ( ). 

The first examples of immobilized microorganisms are discussed above and it can be predicted that when the technique for immobilizing mammalian cells developed further, systems analogous to those discussed in this paper may be used for studying basic cell metabolic phenomena as well as in sensitive biospecific analytical systems. 

Ikebukuro K., Honda M., Nakanishi K., Nomura Y., Masuda Y., Yokoyama K., Yamauchi L, and Karube L, Plow-type cyanide sensor using an immobilized microorganism, Electroanalysis, 8, 876-879, 1996. 

Immobilized microorganisms, in particular ArrAroboc/er simplex and Nocardia rhodocrous, and fungal spores, in particular those from Septomyxa affinis, can also be used to effect dehydrogenations. Dehy-(togenadons may also be advantageously carried out in the presence of hydrocarbon solvents, for example the conversion of 6a-methylhy[Pg.68]

Researchers have also combined reactor types. Guo et al. (1997), for example, designed an external loop airlift reactor that incorporates a fluidized bed within the downcomer section, shown in Figure 10.1. The fluidized bed section is used to immobilize microorganisms on carrier particles in order to protect them from damage. The design is meant for the production of enzymes, biofluidization, and wastewater treatment. Although shear rates were minimized, bubbles were not entrained within the downcomer. Furthermore, the gas-liquid mass transfer coefficient was observed to increase with gas holdup. The result was that the gas-liquid mass transfer was limited due to the fact that global gas holdup for the reactor was strictly defined by the riser gas holdup without any addition by the downcomer. 

One of the main apphcations of polymer cryogels is their use in biotechnology as carriers of cells, bacteria, and enzymes [1, 2]. The advantages of immobilized microorganisms over cultures in suspension include the easier collection and purification of bioproducts, better stability and performance under storage and operational conditions, tolerance against toxic compounds, etc. 

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