2 μm GTBP) (Millipore, USA), dehydrated see more in a graded ethanol series (50%, 70%, 90% and 100%), critical-point dried in CO2 in an EMS 850 (Electron Microscopy Science, USA) and coated with gold palladium alloy in an EMS 550X (Electron Microscopy Science). The coated samples were examined using a Zeiss EVO 50 (Zeiss, Germany). Ten microscope fields, at 3000X magnification, were randomly taken of each isolate on each sampling day. The percentage of coiled forms and bacillus were determined by counting all the cells present in each field. In addition, the average length of 10 randomly selected cells per field was measured. For TEM, 250 μl of culture were fixed

in 0.1 M PBS, pH 7.2 containing 2.5% glutaraldehyde, and 2% formaldehyde. After 90 min at room temperature, cells were washed in PBS and fixed in 1% OsO4 for another 90 min prior to dehydration in a graded ethanol series (30-100%), washed in propylene oxide (PO) and infiltrated in epoxy resin (EMbed 812, Electron Microscopy Sciences, Pennsylvania, USA) following manufacturer’s instructions for soft block GSK2126458 hardness replacing 3:1 PO:Resin mix, 1:3 PO:Resin mix, 1:3 PO:Resin mix, resin washes and polymerized. After microtoming, samples were observed using a Zeiss EM

10C 10CR Transmission Electron Microscope (Zeiss, Germany). Viability of coiled cells To prove that the coiled forms were viable and not degenerative forms, a ‘dilution to extinction’ strategy was used. Cultures from the 14 day microcosm experiment were 10-fold diluted in MS broth until 10-13 and incubated for 48 h at 28±2°C. If tubes showed turbidity

then, 100 μl was inoculated onto MS agar in triplicate and typical F. columnare Vistusertib price colonies were annotated. To further evaluate the survival potential of starved cells, strain ALG-00-530 was selected to determine the membrane integrity of starved versus non-starved cells. Fresh (24 h) and starved (1-month, 3-month, and 5-month) cultures of ALG-00-530 were used for this experiment. Starved cultures were prepared as described before. Membrane potential was estimated with LIVE/DEAD BacLight Bacterial Viability Kit (Invitrogen, USA) following manufacturer’s instructions Leukocyte receptor tyrosine kinase (SYTO 9 and propidium iodine were mixed 1:1 before adding to the cultures). Stained cells were observed under a Zeiss epifluorescent microscope (Zeiss, Germany) using appropriate filters. Green (live) and red (dead) cells from 10 microscope fields were photographed and counted at 400X. Virulence of the coiled forms To test the virulence potential of the starved cells in channel catfish, we challenged channel catfish with fresh ALG-00-530 and 2 week-old starved cultures. Challenge protocols have been described previously in detail [19]. Briefly, challenge experiment consisted of three treatments: fresh (24 h) ALG-00-530, 2 week-old ALG-530, and unchallenged control. Each treatment consisted of three randomized replicates (tanks) containing 10 channel catfish per tank (mean weight: 0.8±0.1 g; mean leght 4.5±0.5 cm).