( ( The cells ) ( ( ( were then ) ( ( lysed ( by exposure ) ) ( to ( four ( freeze-thaw cycles ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NNS cells)) (VP (VBD were) (ADVP (RB then)) (VP (VBN lysed) (PP (IN by) (NP (NN exposure))) (PP (TO to) (NP (CD four) (JJ freeze-thaw) (NNS cycles))))) (. .)))
The cells were then lysed by exposure to four freeze-thaw cycles.
(ROOT (S (NP (NNS Cells)) (VP (VBP have) (NP (CD four) (NNS cycles))) (. .)))