“A cyanobacterium akin to the free-living genus Microcystis living within cells of the apple snail Pomacea canaliculata”

VEGA IA; KOCH E.; GODOY MS.; CASTRO-VAZQUEZ A.

San Luis, Argentina

Congreso; XXIV Reunión Anual de la Sociedad de Biología de Cuyo.; 2006

Sociedad de Biología de Cuyo.

In previous studies we have explored the possible cyanobacterial and endocytobiotic nature of pigmented corpuscles (named C and K bodies) found in the midgut gland of Pomacea canaliculata. Morphological studies showed that C corpuscles are round bodies, 14 μm in diameter, of a brownish-greenish color, which are delimited by outer membrane and an electron-dense wall. On their part, K corpuscles are multilamellar, club-shaped bodies of a dark brown color (approx. 35 μm long and 14 μm wide). Numerous granules of varying sizes, as well as some irregular membranes are observed in C corpuscles. On their part, K corpuscles are formed by a center of coarse granules surrounded by numerous electron-dense lamellae. DNA was found in both C and K corpuscles, while DNA extracted from C corpuscles was purified and used as template for the PCR amplification of the bacterial gene encoding for the 16S rRNA. In the present work, this gene was cloned and sequenced, and was found akin to that of the free-living genus Microcystis (Cyanobacteria, Chroococcales). Also, in situ hybridization with probes recognizing conserved sequences of this gene (for both Bacteria and Cyanobacteria) allowed us to localize ribosomal RNA on both corpuscular types within midgut gland’s epithelial cells. It seems, therefore, that pigmented corpuscles contained within these cells of P. canaliculata are indeed morphs of a chroococcalean cyanobacterium. And it should be stressed that this association seems to be an obligate one for the snail, since we have found such corpuscles in all populations of P. canaliculata that we have sampled so far.