The frozen samples were kept and stored in a 2-ml tube containing liquid nitrogen before cryosubstitution was carried out. The frozen sample was transferred to a microfuge tube containing 2% (wt/vol) osmium tetroxide in acetone and cryosubstituted in a Leica AFS. The sample was warmed from -160°C to -85°C over 1.9 h (rate 40°C/h), check details held at -85°C for 36 h, then warmed from -85°C to

20°C over 11 h (4°C/h). The high-pressure frozen and cryosubstituted samples were then processed into EPON resin and ultrathin-sectioned using a Leica Ultracut Ultramicrotome UC61. The cut sections were placed onto a formvar-coated copper grid and stained with 5% (wt/vol) uranyl acetate in 50% ethanol and with lead citrate. Freeze fracture Verrucomicrobium spinosum cells were LY3039478 concentration swabbed off a plate and resuspended in 20% (vol/vol) glycerol for 1 hr. After rapid freezing, cells were freeze-fractured using a Balzers BAF 300 Unit. Fracturing was performed at -120°C, and

3 nm of platinum/carbon was shadowed onto the samples at an angle of Blasticidin S concentration 45°. A 25 nm layer of carbon was then evaporated on top of this. Samples were taken from the freeze fracture unit and thawed. The replicas were cleaned in 25% chromic acid for 3 days, rinsed 3 times in distilled water and picked up onto 200 mesh copper grids. Immunolabelling of double-stranded DNA Ultrathin-sections of high-pressure frozen and cryosubstituted V. spinosum and P. dejongeii cells on carbon-coated

copper grids were floated onto drops of Block solution containing 0.2% (wt/vol) fish skin gelatin, 0.2% (wt/vol) BSA, 200 mM glycine and 1 × PBS on a sheet of Parafilm, and treated for 1 min at 150 W in a Biowave microwave oven. The grids were then transferred onto 8 μl of primary antibody, (mouse monoclonal IgG anti-double-stranded DNA (abcam) diluted 1:500 in Block solution), and treated in the microwave at 150 W, for 2 min with microwave on, 2 min off, and 2 min on. The grids Glutamate dehydrogenase were then washed on drops of Block solution 3 times, and treated each time for 1 min in the microwave at 150 W, before being placed on 8 μl of goat anti-mouse IgG 10 nm-colloidal gold antibody (ProSciTech) diluted 1:50 in Block solution and treated in the microwave at 150 W, for 2 min with microwave on, 2 min off, and 2 min on. Grids were washed 3 times in 1 × PBS, each time being treated for 1 min each in the microwave at 150 W, and 4 times in water for 1 min each in the microwave at 150 W. The grids were dried and stained with 1% (wt/vol) aqueous uranyl acetate. Three negative controls were carried out for this experiment. Firstly, anti-GFP antibody, an antibody which targeted an antigen not expected to occur in Verrucomicrobia, was used as the primary antibody. Secondly, the block solution with no antibody of any type was used in place of the primary antibody.