Fig. 2

Validation of nematode axenicity status. a To estimate the presence of Xenorhabdus nematophila bacterial cells in Steinernema carpocapsae nematodes, a nematode pellet is homogenized and the homogenate is spread onto agar plates. The absence of X. nematophila colonies on the plates denotes that the nematodes are free of bacterial cells. Bacterial colony forming units (CFU, log scale) are shown in Round 1 and Round 2 of the axenicity assay. SS surface sterilized nematodes. b Diagnostic PCR for detecting the presence or absence of X. nematophila bacteria in surface-sterilized or non-surface-sterilized S. carpocapsae nematodes that were subjected to a single round of the axenicity assay (Round 1 and Round 1: SS) or two rounds of the procedure (Round 2 and Round 2: SS). Symbiotic nematodes served as control. The size of the PCR amplified X. nematophila XptA2 gene is indicated