RELEVANCE OF THE EXOPOLYSACCHARIDE OF MARINE PSEUDOMONAS SP STRAIN S9 FOR THE ATTACHMENT OF CIONA-INTESTINALIS LARVAE

Effects of bacterial exopolymers on the attachment of larvae of the ascidian Ciona intestinalis were examined in the laboratory. A marine Pseudomonas sp. (strain S9) which forms and excretes a peripheral exopolysaccharide during energy and nutrient starvation was used as a test organism. The experiments also focused on inhibition of exopolymer excretion and the use of a transposon-generated mutant that was deficient in the release of peripheral exopolymer. Two modes of larval attachment to surfaces coated with bacteria could be distinguished, depending on the amount of peripheral exopolysaccharide present: active attachment by use of the adhesive organs, and passive attachment due to trapping of the larvae in the exopolymer material. All larvae underwent metamorphosis and could therefore contribute to population recruitment. A similar increase in the extent of attachment in the presence of peripheral exopolysaccharide could be observed for both fertilized and non-fertilized eggs. Our findings show that exopolymers produced by bacteria may increase the extent of attachment of C. intestinalis larvae.