Research On The Biotransformation Of Selenium By Porphyridium Sp.

Porphyridium sp., a unicellar red algae, has a great commercial value and broad application for synthesizing many high-value bioactive substances such as phycobiliprotein, polyunsaturated fatty acids (PUFA), exopolysaccharide and so on. Selenium is one of human essential bio-trace elements, having many physiological and biological functions such as scavenging free radicals, antioxidation, antitumor activity, etc. Porphyridium sp. can enrich and bio-transform selenium when cultured in medium containing sodium, which is an easy and effective way to get organic sele-compounds. Using the strain Porphyridium sp. UTEX637 as a model organism, we investigated the effect of selenium on the algal growth, the major biochemical components and antioxidase activity, the dynamic process of selenium accumulation and its distribution characteristic in the major biochemical components. The results are as follows:(1) Selenium (0.5 mg·L-1) can promote the algal growth. The maximum cell dry weight (4.8 g·L-1) was 0.6g·L-1 more than that of the control, and the yield of extra-polysaccharide reached 180.7 mg·L-1, which was 1.69 times higher than that of the control. The contents of chlorophyll-a,phycobiliprotein are higher than the control.(2) Selenium can improve the antioxidation activity of Porphyridium sp. by increasing the activity of glutathione peroxide (GSH-Px), which can be heightened to 4.31 U and was 1.31 times higher than that of the control. The content of malonaldehyde (MDA) of experimental group was 15.21% less than the control. The activity of superoside dismutase (SOD) and catalase (CAT) did not response at the 0.5 mg·L-1 concentration of selenium.(3) The maximum intracelluar selenium content was 27.99μg·g-1, which was 14 times higher than that of the control; the selenium content of exopolysaccharide was 31.02μg·g-1. The total amount of selenium accumulated by Porphyridium sp. reached 140.16μg per liter culture and the rate of assimilation was 28.03%, and the selenium utilization efficiency of algal cell and exopolysaccharide are 21.91% and 1.12%, respectively.(4) The intracelluar selenium was mainly distributed in polysaccharide which has the selenium content of 7.08μg·g-1 (DW) and accounted for 25.3% of that total celluar selenium content. The selenium contents of water-soluble protein and crude lipids were 5.84μg·g-1 (DW) and 0.89μg·g-1 (DW) which accounted for 20.9% and 3.2%, respectively.