2. Materials and methods
2.1. Recombinant S-layer protein production
Recombinant S-layer protein of A. hydrophila was produced in
order to have sufficient protein for a vaccination trial.
2.1.1. Extraction of DNA from A. hydrophila
A. hydrophila isolate T4 was grown overnight according to
Poobalane et al. [30] and centrifuged at 5000×g for 5min at 4 ◦C.
The pellets were resuspended in 567l Tris ethylenediaminetetraacetic
acid (EDTA) (TE) buffer (10mM Tris–Cl and 1mM EDTA,
pH 8), 30l of 10% (w/v) SDS and 3l of 20mgml−1 proteinase K.
The bacteria were thoroughly mixed and incubated for 1 h at 37 ◦C
before adding 100l of 5M NaCl. The pellets were mixed again
and incubated for 10 min at 65 ◦C after adding 80l cetyltrimethylammonium
bromide (CTAB) in NaCl solution (10%, v/v, CTAB in
0.7MNaCl). The DNA was extracted from the sample with an equal
volume of chloroform: isoamyl alcohol (24:1 ratio) (780l). The
tube was inverted a couple of times and centrifuged at 5000×g for
5min at 4 ◦C. The aqueous phase was transferred to a new tube and
extracted with phenol: chloroform: isoamyl alcohol (25:24:1 ratio).
The contents of the tube was thoroughly mixed and centrifuged at 5000×g for 10 min at 20–22 ◦C before transferring the aqueous
phase to a new tube. The DNA was precipitated with an equal volume
of isopropanol. The contents of the tube were then thoroughly
mixed by inverting the tube a couple of times and centrifuged at
5000×g for 10 min at 4 ◦C. The precipitate was washed with 70%
ethanol by centrifuging at 5000×g for 10 min at 4 ◦C. The supernatant
was removed and the pellets were briefly dried at 20–22 ◦C
for 10 min. The pellets were resuspended in 100l TE buffer and
stored at −20 ◦C until used.