Figure 2.

Schematic of the human gut, indicating unknown inputs to the gut phageome from diet and the environment, highlighting the largely unknown phage composition of the ileum and colon and indicating the relative proportions of phages in the best understood samples: faeces. Circle size provides a rough guide to the relative abundance of phage particles observed in different gut compartments (Zoetendal et al., 2012; Hoyles et al., 2014; Shkoporov and Hill, 2019), but current understanding is still lacking. Most research activity has focused on faecal samples, represented in the lowest pie chart, depicting the relative proportions of different phage groups identified through metagenome analysis, based on Shkoporov and Hill (2019).