Samples were examined by transmission
electron microscopy (TEM; Hitachi H-7650) by co-culturing T. thermophila BF1 with A. hydrophila J-1 in PBSS for 24 h, pelleting the cells and immediately fixing them with 2.5% glutaraldehyde. Tetrahymena thermophila BF1 not co-cultured with A. hydrophila were used as a negative control for observation under electron microscopies. A single selleck inhibitor colony of either A. hydrophila J-1 or NJ-4 was used to start an overnight LB culture at 28 °C and 50 μL of each was then used to inoculate in 5 mL LB, respectively. Once an OD600 nm of the cultures reached 0.8, the supernatants were, respectively, collected and passed through a 0.22-μm pore-size filter membrane. An equal volume of T. thermophila BF1 in PYG media was added selleck to the respective supernatants and cultured at 30 °C without shaking. Tetrahymena thermophila BF1 were counted using a hemacytometer at 0 and 6 h, respectively. Our previous studies suggested that two primary virulence genes, the aerolysin (aerA) and Ahe2 serine protease (ahe2) genes, were present in the strain of A. hydrophila J-1, but not in A. hydrophila NJ-4 (unpublished data). Therefore, the expression levels of the above two
genes were only assessed in A. hydrophila J-1 co-cultured with T. thermophila. After a 4-h co-culture with T. thermophila and A. hydrophila J-1 in PBSS, samples were passed through a 5-μm pore-size filter membrane to collect cells. In addition, the grown A. hydrophila J-1 in the absence of T. thermophila were also collected by centrifugation at 10 000 g for 1 min. Total RNA
was isolated from A. hydrophila J-1 without T. thermophila and from intracellular A. hydrophila J-1 at 4 h as described ROS1 (Hamilton & Orias, 2000). The RNA samples were reverse transcribed to cDNA using a PrimeScript ™ reagent Kit (Takara) according to the manufacturer’s instructions. Primers were designed to amplify aerA and ahe2 (Table 1). The cDNA samples were used for the quantitative real-time PCR analysis, performed using a 7300 Real-Time PCR System (ABI) with SYBR Premix Ex Taq™ (Takara) according to the manufacturer’s instructions. Each PCR reaction (20 μL total volume) contained 10 μL SYBR Green PCR Master Mix (Applied Biosystems, Foster City, CA), 1 μL of each primer (300 nM final concentrations), 3 μL of ddH2O and 0.4 μL of cDNA. The thermal cycling protocol was as follows: 94 °C for 2 min, followed by 40 cycles of 94 °C for 10 s and 60 °C for 30 s. Each sample was run in triplicate. The 16S rRNA gene as the internal control was also amplified under the same conditions to normalize reactions. Gene expression levels were calculated using the following formula: (Livak & Schmittgen, 2001). The population growth dynamics of two A. hydrophila strains in the presence of T. thermophila BF1 were examined. The growth of bacteria was followed by measuring the absorbance of the suspension at 450 nm every hour. Co-culture with T. thermophila BF1 did not affect A.