Colon, microorganisms

The use of microbial siderophores by dicotyledonous plants appears to involve uptake of the entire metallated chelate (42-44), or an indirect process in which the siderophore undergoes degradation to release iron (45). As demonstrated in initial studies examining this question, there was concern that iron uptake from microbial siderophores may be an artifact of microbial iron uptake in which radiolabeled iron is accumulated by root-colonizing microorganisms (46). Consequently, evidence for direct uptake of iron from microbial siderophores has required the use of axenic plants. In experiments with cucumber, it was shown that the microbial siderophore ferrioxamine B could be used as an iron source at concentrations as low as 5 pM and that the siderophore itself entered the plant (42). 

These data strongly suggest that siderophore production by root-colonizing microorganisms is induced only at a level neeessary to supplement that which is not provided by phytosiderophores and organic acids released during the plant iron stress response. Thus, the plant iron stress response may control iron availability to microorganisms in the rhizosphere. 

Bragger JL, Lloyd AW, Soozandehfar SH, Bloomfield SF, Marriott C, Martin GP (1997) Investigations into the azo reducing activity of a common colonic microorganisms. Int J Pharmaceut 157 61-71... 

Creation of a suitable environment for the growth of colonic microorganisms, such as Bacteroids, Eubacterium, and Enterobacteriaceae, among others ... 

The colon serves four major functions. They are 1) creation of a suitable environment for the growth of colonic microorganisms such as Bacteroids, Eubac-terium, and Enterobacteriaceae 2) storage reservoir of fecal contents 3) expulsion of the contents of the colon at a suitable time and 4) absorption of water and Na from the lumen, concentrating the fecal content, and secretion of K+ and HCOs . The active secretion of K+ is stimulated by mineralocorticoids. 

The colon seems to be the essential site for the release of free hydroxycinnamic acids and ftieir absorption. In a study of the uptake of Relabeled hydroxycinnamates bound to spinach cell walls in rats, the foregut was localized as the site of absorption after the release of the labeled hydroxycinnamic acids form flie cell wall by colonic microorganisms, when 25% of flie ingested dose of label was found to be associated with body tissue after only 2 h [32]. On flie basis of flie results on absorption, metabolism, degradation, and elimination of chlorogenic acid in humans presented, its metabolic fate in... 

The tannins that reach the large intestine could be degraded by colonic microorganisms. The studies on metabolism of tannins by intestinal microbiota in ruminants are limited. Colonic microbiota of humans apparently metabolized the polymeric CT extensively after 48 h of incubation under in vitro anaerobic conditions (Deprez et al. 2000). Phenylacetic, phenylpropionic and phenylbutyric acids were the main metabolites detected, although, they represented only 2.7% of the initial radioactivity from the substrate (Deprez et al. 2000). 

It is accepted in regulatory circles that the mass of colon contents is agreed to be 220 g and the weight of a human is 60 kg. The fraction of oral dose available is described in the Guideline, The fraction of an oral dose available for colonic microorganisms should be based on in vivo measurements for the drug administered orally. Alternatively, if sufficient data are available, the fraction of the dose available for colonic microorganisms can be calculated as 1 minus the fraction (of an oral dose) excreted in urine. Human data are preferred, but in its absence, non-ruminant animal data are acceptable. In the absence of data to the contrary, it is assumed that metabolites have antimicrobial activity equal to the parent compound. The fraction may be lowered if the applicant provides... 

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