Cindy Boer

220 | Chapter 5.1 ences in the predicted functional pathways between children and adults, were observed in antibiotics synthesis pathways. The vancomycin biosynthesis pathways were signifi- cantly higher in the gut microbiome of children as compared to adults. Vancomycin is a glycopeptide with activity against gram-positive bacteria, while gram-negative bacteria are resistant to this drug because of their distinct cell-wall[59,60]. On the other hand, biosynthesis of ansamycin was higher in adults than in children. Ansamycin is anoth- er antibiotic with activity against gram-positive, as well as gram-negative bacteria[61]. These findings indicate potential differential anti-bacterial activities between the mi- crobiota of children as compared to adults, which appears to be in line with our obser- vation of higher relative abundances of gram-negative bacteria in the gut microbiota of children. However, the exact role of antibiotic production in modulating the microbiota profiles of children and adults remains to be shown. Another difference identified by predictive functional pathway analysis was the differential biosynthesis of vitamin B classes by the gut microbiota of children and adults. Children’s gut microbiomes are associated with pathways related to increased biosynthesis of vitamins B2, B6, and B9 (folate), while in adults vitamin B1 and B5 bio- synthesis pathways appear to be increased. This predictive finding could be linked to age-dependent differences in, for example, the requirement for folate, which is particu- larly important for cell division and growth during pregnancy and childhood. In children, the enrichment of putative colonization-related pathways involving biofilm formation, flagella assembly and LPS biosynthesis, may provide insights into the development of intra-microbiome and host-microbiome interactions, and also be linked to our observation of higher relative abundances of gram-negative bacteria in children - LPS is a major constituent of the cell wall of gram-negative bacteria. Finally, observing photosynthesis pathway (ko00195) in the functional data could be explained by the presence of Cyanobacteria in our datasets, as Cyanobacteria are photosynthet- ic bacteria. Likely, the photosynthesis pathways detected in the PICRUSt analysis were derived from these Cyanobacteria. The presence of Cyanobacteria in the gut may have a dietary origin[62]. As with all studies, the current study was not free of limitations. One of the main discussion points involves the fact that stool samples were not directly frozen and im- mediately stored at −80 °C. For logistical reasons relating to the large scale cohorts re- cruited, we depended on postal delivery of home-collected stool samples to the research laboratory. Several studies have addressed the effects on microbiota composition when sample collection is performed at room temperature[63-68], and observed that longer periods of storage at ambient temperature may affect microbiota profile composition