Role of Intestinal Microbiota in Ulcerative Colitis
Role of Intestinal Microbiota in Ulcerative Colitis
Role of Intestinal Microbiota in Ulcerative Colitis
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Theoretical part<br />
12<br />
2. The colonic environment<br />
2.3. Difference <strong>in</strong> microbial community<br />
Even though several species <strong>of</strong> the colon are able to <strong>in</strong>habit both the mucosal and the lum<strong>in</strong>al<br />
environment, the mucosal microbial community has shown to differ from the lum<strong>in</strong>al community<br />
(Zoetendal et al., 2002;Macfarlane et al., 2005;Macfarlane, 2008;Van den Abbeele et al., 2011a).<br />
Additionally, literature have revealed that dom<strong>in</strong>ant phylogenetic groups <strong>of</strong> mucosal microbial<br />
communities are similar <strong>in</strong> the ascend<strong>in</strong>g colon, descend<strong>in</strong>g colon, and rectum, but with high <strong>in</strong>ter‐<br />
<strong>in</strong>dividual variations (Zoetendal et al., 2002;Lepage et al., 2005;Eckburg et al., 2005;Wang et al.,<br />
2005a). In contrast, it has been demonstrated that lum<strong>in</strong>al microbial communities differ<br />
depend<strong>in</strong>g on colonic region (Pochart et al., 1993;Marteau et al., 2001). This suggests that<br />
different environmental conditions found throughout the colonic lumen (described <strong>in</strong> section 1.2)<br />
may affect the composition <strong>of</strong> lum<strong>in</strong>al bacteria, whereas the composition <strong>of</strong> mucosal bacteria is<br />
more <strong>in</strong>fluenced by host factors (described section 2.1). It is also plausible that the niches <strong>of</strong> the<br />
lumen and the mucus select a microbial population that may display different roles <strong>in</strong> the host. A<br />
recent study by Derrien et al. (2011) has demonstrated that germ‐free mice mono‐cultured with<br />
Akkermansia muc<strong>in</strong>iphila (Gram‐negative, strictly anaerobic muc<strong>in</strong>‐degrad<strong>in</strong>g bacterium) or<br />
Lactobacillus plantanum (Gram‐ positive bacterium that utilize dietary carbohydrates but is<br />
<strong>in</strong>capable <strong>of</strong> utiliz<strong>in</strong>g muc<strong>in</strong>) led to different mucosal transcriptome changes depend<strong>in</strong>g on<br />
colonization <strong>of</strong> the different bacteria. L. plantarum was exclusively located <strong>in</strong> the colonic lumen<br />
and <strong>in</strong>duced expression <strong>of</strong> genes <strong>in</strong>volved <strong>in</strong> regulation <strong>of</strong> lipid and fatty acid metabolism, whereas<br />
A. muc<strong>in</strong>iphila colonized the colonic mucus <strong>of</strong> the mice and <strong>in</strong>duced expression <strong>of</strong> genes <strong>in</strong>volved<br />
<strong>in</strong> regulatory immune processes. These results could imply that the mucosal microbiota are more<br />
<strong>in</strong>volved <strong>in</strong> <strong>in</strong>teraction with epithelial and immune cells compared to the lum<strong>in</strong>al microbiota, s<strong>in</strong>ce<br />
they reside closer to the IECs. Hence, the difference <strong>in</strong> bacterial community structure is likely<br />
driven by factors such as differential substrate availability (e.g. mucus versus undigested dietary<br />
residues) and host‐microbe <strong>in</strong>teractions. Figure 3 illustrates the mucosa and lumen <strong>of</strong> the colon.