With one-factor-at-a-time method and orthogonal experiment, the optimal fermentation condition of strain F-6 was determined. Besides, the decomposition effect by agarase on P. yezoensis cells was studied. Main procedures of experiment of decomposition effect were 1) centrifuged the fermentation broth at 6000g for 30min to obtain supernatant for culture; 2) ultrafiltrated the supernatant and then mixed with l mol/L permeabilization agents; 3) filtrated the mixture for removing bacteria by 0.22 μm separate film; 4) decomposed P. yezoensis tissue for producing protoplasts; 5) poured the collected protoplasts into hyperosmotic and sterilized in sea water with 1% PESI; 6) cultivated the protoplasts in 20°C in light scheme of 12 h/day at 1500 - 2000 lx until the salt concentration was gradually declined to normal sea water level. We also examined the healthy condition of the protoplasts, typical development of cells and their survival rate.

The optimal fermentation condition of strain F-6 was agar 0.7%; yeast powder 0.3%; peptone 0.5%; NaCl 2.0%; K₂HPO₄ 0.1%; MgSO₄?7H₂O 0.05%; FeSO₄?7H₂O 0.002%; CaCl₂ 0.02%; and initial pH 7.5. The optimal temperature and duration were 26°C and 36h, respectively, at which the highest agarase activity reached 631.6 U/ml. The experiments of decomposition effect of agarase on P. yezoensis cells and protoplast cultivation showed that the agarase could easily decompose P. yezoensis tissue into protoplasts at production rate of about 3×10⁶ protoplasts per gram of the tissue. The optimal duration of enzymatic hydrolysis to P. yezoensis was 3.5h. The permeabilization agent of glucose (1 mol/L) could obviously improve the production rate and survival rate of the protoplasts. The protoplasts could develop into callus at survival rate of approximately 60%.