Removal of Epiphytic Diatom Licmophora ehrenbergii Attaching on Porphyra Thalli by Proteolytic Enzyme.

Epiphytic diatoms attaching on cultivated Porphyra foliose thalli deteriorate the luster and color of dried sheets of Porphyra. Epiphytic diatoms secrete mucus to attach to substrata such as Porphyra foliose thalli. Certain proteases potentially dissolve this mucus, so we studied the effects of proteolytic enzyme produced by Aspergillus melleus on the removal of epiphytic diatoms. When Porphyra foliose thalli attached with a large number of epiphytic diatoms such as Licmophora ehrenbergii were treated with the proteolytic preparation (TPN-1) at 25°C, epiphytic diatoms were removed from Porphyra foliose thalli depending on the concentration of TPN-1 and the duration of the treatment. When the cultivated Porphyra foliose thalli heavily attached with L. ehrenbergii was treated with the seawater containing 0.02% TPN-1 at about 8°C for 3.5h in a washing tank used for making dried sheets of Porphyra, the cell numbers of diatoms ataching to Porphyra foliose thalli obviously decreased. A scanning electromicroscopic study showed the process of dissolution of the mucus secreted from diatoms and the removal of these attaching diatoms from the Porphyra foliose thalli after the treatment with TPN-1. The treatment with TPN-1 improved the luster and color of dried sheets of Porphyra without influencing the composition of free amino acids.