Retention of bacteria

For sterile filtration, filterabUity and vahdation experiments are typically conducted at the laboratory scale to determine the size of the large-scale system and verify the absolute retention of bacteria with the actual process solution and operating conditions. 

Lukaszewicz et al14 has postulated an "adsorptive" mechanism to explain the excellent retention of bacteria by membranes with some pores larger than the microorganism. He contends that the adsorptive sequestrations of the membrane are more important than the geometric restraints of sieving. 

The earliest morphological change in the sebaceous follicle is an abnormal follicular epithelial differentiation, which results in ductal hypercornification. Cornified cells in the upper section of the follicular canal become abnormally adherent. Comedones represent the retention of hyperproliferating ductal keratinoc-ytes in the duct. Several factors have been implicated in the induction of hyperproliferation sebaceous lipid composition, androgens, local cytokine production (IL-i, EGF) and bacteria (P. acnes). 

Catechins Bacteria Tetracycline efflnx pinnp 8-lactams Increased intracellular retention of tetracycline [66]... 

A component of the ribotide reductase complex of enzymes, protein Ba, has been shown to contain two non-heme iron atoms per mole (77). This enzyme plays a vital, albeit indirect, role in the synthesis of DNA. Curiously, the lactic acid bacteria do not employ iron for the reduction of the 2 hydroxyl group of ribonucleotides. In these organisms this role has been assumed by the cobalt-containing vitamin Bi2 coenzyme (18). The mechanism of the reaction has been studied and has been shown to procede with retention of configuration (19). 

Retention of much of the cytoplasmic chemistry while novel chemistry was largely placed in the periplasm of bacteria or at least on the membrane surface facing it, e.g. the management of sulfate, ferric ion or oxidised nitrogen, often involving Mo, as a source of energy. 

Htc-552 when expressed in E. coll undergoes spontaneous cytoplasmatic maturation (covalent haem attachment), in contrast to the usual periplasmatic maturation route for bacteria. NMR spectroscopy together with other techniques were employed to characterize Htc-552 expressed in the cytoplasm and periplasm of E. coli. It was shown that the cytoplasmatic product exhibits lower thermostability (r i = 85°C compared to the periplasmatic Tm = 90°C) because of structural anomalies in the region of the N-terminal helix, due to the retention of the N-terminal methionine and not to haem attachment errors. 

Fischer, H., A. Sachse, C. E. W. Steinberg, and M. Pusch. 2002. Differential retention of dissolved organic carbon by bacteria in river sediments. Limnology and Oceanography, in press. 

The predilection of bacteria to associate with surfaces is the primary organizing principle of community structure. ZoBell (1943) presented a conceptual model of this organization surfaces concentrate nutrients bacterial attachment to surfaces maximizes concentration gradients and reduces diffusion distances packing cells on surfaces improves retention of extracellular enzymes. Over the next 40 years, the study of attached microbial communities became an integral part of several fields (see Chapter 12). The importance of periphyton, or aufwuchs, in stream metabolism was established (Hynes, 1970 Geesey et al., 1978 Stevenson et al., 1996). Comparative studies of community organization and activity in relation to substratum produced a taxonomy for attached communities epilithon, epiphyton,... 

Aside from actual incorporation of this substance into foods, benefits may be derived in other ways. For example, one such suggested use76 is for the formation of a coating on meats, fruits, and vegetables, in conjunction with antimold substances, for protecting the foodstuffs from bacteria and molds. It is also noteworthy that the addition of carboxymethylcellulose to foods, prior to dehydration, is said to improve the retention of natural flavors. 

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