Page 45 - Read Online

Kreuze et al. Microbiome Res Rep 2025;4:7 https://dx.doi.org/10.20517/mrr.2024.51 Page 3 of 14

Figure 1. A schematic illustration of the colonization bottleneck and its effect on the diversity and abundance of bacteria and MGEs
inherited from mother to infant. Only a subset of bacteria and associated MGEs might be able to pass the colonization bottleneck due to
selection and stochastic chance events. The different bacterial taxa and MGEs are represented by different colors and symbols. MGEs:
Mobile genetic elements.

Figure 2. Two alternative routes of MGE inheritance enable them to cross the colonization bottleneck. In the vertical transmission
scenario, MGEs are inherited together with their bacterial host during the cell division and this relationship could be beneficial for both
(mutualism). In the horizontal transmission scenario, MGEs could move to any successfully colonizing bacterial host, breaking
taxonomic associations between the bacterial hosts and their MGEs. This relationship could be considered parasitic as the fitness
interests of MGEs are not aligned with those of their host. Most MGEs are capable of both modes of transmission and could hence be
[25,26]
considered as facultative mutualists (or parasites) . MGE: Mobile genetic element.