Visualizing Bacterial DNA in Nematode Guts

The undigested bacteria DNA in the gut lumen was stained by vital DNA-binding dye SYTO11 (Molecular Probe, Invitrogen) as previously described [21 (link)]. The L3 and L4 stage worms were collected and washed twice with M9 buffer then transferred into a 1.5 ml of tube containing SYTO11 dye (10 μM in M9) at RT for 2 h in the dark. The stained worms were washed twice with M9 and recovered on Escherichia coli OP50 seeded NGM (nematode growth medium) plates at RT for 1 h in the dark. After recovery, the worms were washed twice with M9 and anaesthetized by lavamisole (200 μM), then mounted on to 2% agar pads and observed under a fluorescence microscope (Leica DM2500) with a FITC filter.