2.2. Fluorescence in situ hybridisation (FISH)
Entire soil blocks of lichen material were fixed immediately
after sampling in 4% paraformaldehyde (PFA) for 8 h. Material was
washed three times with 1×
PBS in order to remove paraformaldehyde.
The fixed material was stored in 1×
PBS and 96% EtOH (1:1)
at
−20 ◦C prior to subsequential procession. Small fragments of the
soil block of about 1 cm2 (lichen thallus together with the underneath
soil) were embedded in water or in the O.C.T. Tissue Tek
embedding solution (Sakura, Finetech Europe BV, Zoeterwoude,
Netherlands) and cut with a cryotome (Leica CM 3000, Heidelberg,
Germany) into 30 m thick sections. The frozen sections were
transferred with a sterilized and cooled needle in 1×
PBS/96% EtOH
(1:1) solution. Up to 8 tubes were prepared for each lichen sample
and stored at
−20 ◦C. The amount of stored section is sufficient
to perform up to 10 replicates, corresponding to 10 hybridization
experiments with different sets of FISH probes.