Diversity of culturable alginate lyase-excreting bacteria associated with Sargassum

Large numbers of bacteria live on the surface of various brown algae and can produce alginate lyases to consume alginate,an important component of the cell wall of brown algae.Sargassum is a genus of the largest canopyforming brown algae of more than 150 species,which are widely distributed in tropical and subtropical environments.However,our knowledge about the epiphytic bacteria and the alginate lyase-excreting bacteria from Sargassum is still primitive.Here,we investigated the diversity of the culturable epiphytic bacteria and alginate-degrading bacteria from Sargassum samples collected from the coastal seawaters of Shandong Province,China.In total,37 strains belonging to 21 genera in 3 phyla were isolated,including 15 previously unreported genera,of which Vibrio(6/37)and Pseudoalteromonas(5/37)are the dominant genera.Eight strains,mainly Vibrio and Pseudoalteromonas species,were further identified as alginate lyase-excreting strains that can utilize alginate for growth.The extracellular alginolytic activity of the 8 strains was determined,and strains Vibrio sp.C42and Pseudoalteromonas sp.M9 showed the highest activity.These results provide a better understanding of brown algae epiphytes and alginate-degrading bacteria,and are fundamental for further studies on the interactions between brown algae and their epiphytes.