Abstract: This work is to isolate,screen and identify the effective agarase-producing strain from Gracilaria lemaneiformis collected from Nan'ao Island,Guangdong province,for building a foundation for the utilization of agarase. Four different screening culture-mediums were used to screen the agarase-producing bacterium,the morphology,physiological and biochemical properties were employed to identify the isolated strain,and phylogenetic tree was constructed. DNS was adapted to determine the enzyme activity of the agarase,to study the type of the agarase from the strain,and to draw its growth curve and fermentation curve. As results,an effective agarase-producing strain ZQM2017 was isolated from the samples of G. lemaneiformis,which was a gram-negative bacterium,its 16S rRNA sequence was 99% homologous to 52 strains of Vibrio species in the database of NCBI. Combining with the morphological and physiological-biochemical characteristics,it was identified the strain ZQM2017 as Vibrio alginolyticus. The type of agarase by V. alginolyticus ZQM2017 was both α-agarase and β-agarase. Under the condition of 180 r/min and 28℃,the logarithmic phase of the strain was between 3 h to 9 h and the enzyme obviously produced at 5 h,and the enzyme activity of agarase from V. alginolyticus ZQM2017 reached 109.87 U/mL after fermenting for 46 h. In conclusion,the marine bacterium ZQM2017 isolated and screened independently from Nan'ao Island was identified as V. alginolyticus ZQM2017,and can secret α-agarase as well as β-agarase with the initial enzyme activity of 109.87 U/mL.

Key words: agarase, Vibrio alginolyticus, screening and identification, 16S rRNA