ABSTRACT
The bryozoans
Bugula neritina
and
Bugula simplex
harbor bacteria in the pallial sinuses of their larvae as seen by electron microscopy. In
B. neritina
, the bacterial symbiont has been characterized as a gamma-proteobacterium, “
Candidatus
Endobugula sertula.” “
Candidatus
E. sertula” has been implicated as the source of the bryostatins, polyketides that provide chemical defense to the host and are also being tested for use in human cancer treatments. In this study, the bacterial symbiont in
B. simplex
larvae was identified by 16S rRNA-targeted PCR and sequencing as a gamma-proteobacterium closely related to and forming a monophyletic group with “
Candidatus
E. sertula.” In a fluorescence in situ hybridization, a 16S ribosomal DNA probe specific to the
B. simplex
symbiont hybridized to long rod-shaped bacteria in the pallial sinus of a
B. simplex
larva. The taxonomic status “
Candidatus
Endobugula glebosa” is proposed for the
B. simplex
larval symbiont. Degenerate polyketide synthase (PKS) primers amplified a gene fragment from
B. simplex
that closely matched a PKS gene fragment from the bryostatin PKS cluster. PCR surveys show that the symbiont and this PKS gene fragment are consistently and uniquely associated with
B. simplex
. Bryostatin activity assays and chemical analyses of
B. simplex
extracts reveal the presence of compounds similar to bryostatins. Taken together, these findings demonstrate a symbiosis in
B. simplex
that is similar and evolutionarily related to that in
B. neritina
.