Fig. 4: Evolutionary transition from a free-living to a host-associated lifestyle in Rickettsiales ancestors.
From: The evolutionary origin of host association in the Rickettsiales
Proposed lifestyle of LRCA and LhRCA in blue boxes at the bottom indicating marine environments. Rickettsiales cells are depicted as ellipsoid cell models in brown and blue for LRCA and LhRCA, respectively. Reconstructions of key genomic features of ancestors are depicted in cell models in the respective boxes. Arrow in the centre indicates evolutionary transition from LRCA to LhRCA and grey boxes above and below show gains and losses of genomic traits, respectively. Orange and blue arrows indicate metabolic pathways related to sulfate assimilation or central carbon metabolism, respectively. Abbreviations in the figure refer to genes encoding for the tight adherence (Tad) pili; type 4 pili (T4P); type I (T1SS) or rvh type IV (T4SS) secretion systems; Pel-like exopolysaccharide (EPS) synthesis; tricarboxylic acid (TCA) cycle; electron transport chain complexes (C) I-V; Sec-, Tat- and TolC-mediated protein secretion pathways (Sec, Tat and TolC, respectively).
