Monoxenic (gray) or axenic (black) cultures are denoted by colored boxes. The gradients indicate uncertainty in when the culture type was switched. The dates show the year of isolation or when the strain was moved to another laboratory. Underscored dates mark the dates of cryogenic preservation. In 1951, Bristol was isolated by L.N. Staniland and Warwick Nicholas. The strain was kept in Liverpool first as a monoxenic culture and later as an axenic culture []. In 1957, it was shipped to the Kaiser Foundation Research Institute in Richmond, California. During early laboratory propagation, both axenic and monoxenic cultures were maintained. Later, the monoxenic culture was discontinued and the axenic culture continued []. The LSJ1/LSJ2 strains originate from this axenic culture [, ], as does N2. It is unclear when exactly the LSJ1/LSJ2 lineage split from N2 []. In 1963, Brenner received an axenic culture containing C. elegans [], which was cryogenically preserved by John Sulston in 1969 []. The LSJ1 strain was cryogenically preserved in 1995 [, ] and the LSJ2 strain in 2009 [].

Natural C. elegans strains aggregate at the edges of the bacterial lawn (orange) when propagated in laboratory conditions on monoxenic agar plates (left diagram). The edges of the bacterial lawn have lower than ambient oxygen concentrations (approximately 13%, center diagram). Wild C. elegans strains respond to this oxygen gradient and prefer lower oxygen concentrations in the presence of bacterial food []. The abnormal N2 strain is less sensitive to oxygen concentrations and does not aggregate at the edges of the bacterial lawn (right diagram). This difference in aerotaxis or oxygen preference leads to different aggregation and lawn leaving behaviors [, , , , ]. Because of these behavioral changes, strains also differ in exposure to pathogens [, , ]. Additionally, the aggregation behavior might cause a chronic mild starvation state, which results in a reduced growth rate [], reduced fecundity [], altered gene expression [, ], increased crawling speed [], and reduced quiescence during lethargus [].