Gene content enrichment profiles of early and late colonizer strains. Enrichment analysis was carried out using criteria IV (Table 2). Both early and late colonizers show significant enrichments (p = 0.02 and p = 0.05, respectively). The complete distributions of possible enrichment profiles are shown in Additional file 1: Figure S5. EDM1c is an early colonizer that is clonally related to the late colonizer EDM123c. EDM123c maintains the early colonizer genomic profile but has lost genes found in the early colonizer profile.