ABSTRACT
Symbiotic bacteria occur in the intestine of Echinocardium cordatum and other spatangoid species (deposit feeding echinoids). In E. cordatum, these bacteria form spherical bodies called nodules. Nodule formation results from the growth of mat-structured communities around large detrital particles from the gut content. Do the nodules from different host species share common features? The present work aims to answer this question by comparing first, the bacterial symbionts collected in 3 distinct populations (Mediterranean, East Atlantic, and North Sea) of E. cordatum and secondly, the bacterial symbionts collected in a phylogenetically distinct host, Meoma ventricosa. Results indicated that the basic morphological structure of the nodule is similar in all investigated hosts. The bacterial consortia also reveal some consistency in its composition. Interestingly, preliminary molecular analyses (DGGE, 16S rRNA sequencing and FISH) indicate that filamentous delta Proteobacteria predominate in all nodules. The significance of these observations will be discussed both in term of symbiosis functioning and specificity.
