Bacterial communities associated with the sea squirts of the genus Ecteinascidia from the Red Sea and Florida

Ecteinascidin 743 (Et 743) is a potent anticancer compound originally isolated from the ascidian Ecteinascidia turbinata and related species. Its structural similarity to bacterial secondary metabolites suggests that symbiotic bacteria may be the true source of this compound. This study used multiple genetic markers to identify Ecteinascidia species and characterize their associated microbial communities. While 18S rRNA and coxI genes were highly conserved and insufficient for resolving tunicate phylogeny, analyses revealed persistent, species‑specific bacterial associates across samples from the Mediterranean and Atlantic. Notably, “Candidatus Endoecteinascidia frumentensis,” previously known only from E. turbinata, was also found in E. thurstoni and other Ecteinascidia spp. Although its role in Et 743 biosynthesis remains unconfirmed, these findings expand our understanding of ascidian–microbe symbioses and provide a foundation for future studies in culturing, metagenomics, and identification of candidate biosynthetic genes.