and

Chryseobacterium spp. isolates were used as positive see more and negative controls. rpoC qPCR design and test of primers DNA was extracted using InstaGene kit [Bio-Rad, Hercules (CA), USA]. Partial DNA dependent β’ subunit RNA polymerase (rpoC) gene sequences were amplified based on the RNA polymerase β’ subunit primers sequences described by Griffiths et al. [49] with the addition of sequence tags UP1s and UP2sr (rpoC_F 5’- GAAGTCATCATGACCGTTCTGCAATHGGNGARCCNGGNACNCA-3’ and rpoC_R 5’- AGCAGGGTACGGATGTGCGAGCCGGNARNCCNCCNGTDATRTC-3’; synthesized by Microsynth, Switzerland) to increase sequencing performance [50]. The PCR reaction was carried out in a total volume of 50 μl using 2.5 U HotStarTaq DNA Polymerase (QIAGEN-Switzerland), Alpelisib manufacturer 7 mM MgCl2, PCR Buffer 1X (QIAGEN-Switzerland), 0.2 mM dNTP (Roche, Switzerland), 0.2 μM of each forward and reverse primer, and 5 μl of InstaGene DNA extract. The thermal cycle started with 15 min HotStarTaq activation at 95°C followed by 36 cycles of 1 min at 94°C, 90 s at 55°C, 1 min at 72°C and eventually an elongation cycle of 7 min at 72°C. Sequences (GenBank access numbers JX657163-

JX657284) obtained from the rpoC gene general PCR were aligned using MEGA4 [51] and screened for a conserved species-specific fragment that would be used to design a set of primers and a TaqMan probe targeting specifically F. psychrophilum. Primers F.psychro_P1F 5’-GAAGATGGAGAAGGTAATTTAGTTGATATT-3’, F. psychro_P1R 5’- CAAATAACATCTCCTTTTTCTACAACTTGA-3’ and a minor groove binder (MGB), and probe F. psychrophilum_probe Glutathione peroxidase 5’- AAACGGGTATTC TTCTTGCTACA -3’ (Applied Biosystems) labeled with FAM were tested in silico[52] and with BLAST (Basic local alignment

search tool [53]). The primers amplified a fragment of 164 bp. PCR was carried out in a final volume of 25 μl containing 1X Taq PCR Master Mix Kit (QIAGEN, Switzerland), 0.3 μM primers F. psychro_P1F and F. psychro_P1R, and 2.5 μl of genomic DNA. Conditions for amplification were 94°C for 1 min followed by 35 cycles of 94°C for 30 s, 56°C for 35 s and 72°C for 30 s, with a final elongation cycle of 7 min at 72°C. DNA of F. psychrophilum, Flavobacterium spp. and other bacterial species isolated from soil, water and fish were used to test sensitivity and specificity of the primers. All tested bacteria and their origin are listed in Table 1. qPCR cycling parameters The qPCR was carried out in a final volume of 20 μl containing 1× TaqMan Environmental Master Mix v.2.0 (Applied Biosystems), 0.9 μM of each primer, 0.2 μM of F. psychrophilum probe, 1X of internal control Exo IPC Mix, 1× of IC DNA (TaqMan Univ. MMix w Exog IntPostC, Applied Biosystems), and 2 μl of template DNA. An internal control was added to each reaction to check for PCR inhibitors. The run consisted of two cycles at 50°C for 2 min and 95°C for 10 min, followed by 40 cycles at 95°C for 15 s and 60°C for 1 min. All assays were carried out in triplicates.