The Coxiella burnetii cryptic plasmid is enriched in genes encoding type IV secretion system substrates.
Voth DE, Beare PA, Howe D, Sharma UM, Samoilis G, Cockrell DC, Omsland A, Heinzen RA. The Coxiella burnetii cryptic plasmid is enriched in genes encoding type IV secretion system substrates. J Bacteriol. 2011 Apr; 193(7):1493-503.