The alien species Caulerpa cylindracea and its associated bacteria in the Mediterranean Sea

Although several studies have investigated bacterial-algal interactions, the bacterial component has often not been identified, and the ecological role of bacterial-algal associations is still unclear. In the present study two different approaches (molecular and culture) have been used to characterize the bacterial community associated with the invasive alga Caulerpa cylindracea (Sonder) over time, in a coastal area of the Mediterranean basin. C. cylindracea is an invasive macroalga in the Mediterranean Sea, able to colonize several types of substrates. Traditional culture-based and PCR-SSCP methods have been used to analyze the bacterial community. Molecular traces of Gammaproteobacteria belonging to the genera Shewanella and Vibrio have been found by both approaches on the surface of C. cylindracea consistently in time, along with those of an unknown species belonging to the Rhodobacteraceae family. Other taxa belonging to Bacillus, Pseudoalteromonas, Tropicibacter, Photobacterium, Exiguobacterium, Kocuria, Ruegeria, and Marinobacter genera have been discovered by culture-based approach. PCR-SSCP method has shown traces of an unknown species of the Bacteroidetes phylum and the Granulosicoccus genus. Our results suggest that C. cylindracea hosts a bacterial assemblage scarcely variable with time. Further studies are needed to clarify the nature of this alga-bacteria association and the potential role in the spreading of this alga using a holistic view considering the seaweed with associated bacteria as an essentially unique meta-organism.