TABLE 3.

History of the research on the endosymbionts of free-living amoebae and other amoeba-resistant microorganisms^a

Yr	Hypothesis or discovery	Microorganisms(s)	Author(s)
1856	Presence of slender thread in Paramecium caudatum	Paramecium caudatum	Müller et al.
1879	Concept of symbiosis	Lichen	De Bary
1954	Lysis of a free-living amoeba due to bacterial infection	Free-living amoeba and bacteria	Drozanski et al.
1975	Presence of an endosymbiont within Acanthamoeba	Acanthamoeba and bacteria	Proca-Ciobanu et al.
1978	Role of free-living amoeba as a reservoir of pathogenic facultative intracellular bacteria	Acanthamoeba and mycobacteria	Krishnan-Prasad et al.
1979	Cryptococcus neoformans may survive within Acanthamoeba	Acanthamoeba and C. neoformans	Bunting
1980	Role of free-living amoebae in transmission (expelled vesicles)	Acanthamoeba and Legionella	Rowbotham
1981	Increased viability of enteroviruses adsorbed on Acanthamoeba: carrier role	Acanthamoeba and enteroviruses	Danes et al.
1986	Role of free-living amoebae in the selection of virulence traits (motility)	Acanthamoba and Legionella	Rowbotham
1988	Protection of internalized bacteria from chlorination	Enterobacteriaceae and Tetrahymena	King et al.
1992	Role of free-living amoeba in the susceptibility of the internalized bacteria to biocides	Acanthamoba and Legionella	Barker et al.
1995	Role of free-living amoeba on the antibiotic susceptibility of the internalized bacteria	Acanthamoba and Legionella	Barker et al.
1996	Role of free-living amoeba in the adaptation of the internalized bacteria to life within human macrophages	Acanthamoba and Legionella	Bozue et al.
1997	Environmental endosymbionts of free-living amoebae as emerging human pathogens	Parachlamydia acanthamoebae	Birtles et al.
1998	Horizontal transfer of clusters of genes contributing to symbiotic life: “symbiosis island”	Mesorhizobium loti	Sullivan
1998	Mitochondria originated by endosymbiosis: relationship between genomes of Rickettsia prowazekii and mitochondria	Rickettsia prowazekii	Andersson et al.
2000	First genome of a symbiont (of aphids)	Buchnera aphidicola	Tamas et al.
2003	Discovery of mimivirus, a giant virus naturally infecting free-living amoebae	Acanthamoba and mimivirus	La Scola et al.

^aDuring the last 5 years, the increased availability of molecular tools and data has led to a better understanding of the relationships between free-living amoebae and amoeba-resistant microorganisms.