HR: 1340h
AN: B43E-1650    [Abstracts]
TI: Evolutionary implications of endosymbiont diversity within lucinid bivalves
AU: * Garcia, A M
EM: agree15@lsu.edu
AF: Department of Geology & Geophysics, Louisiana State University, Baton Rouge, LA 70803,
AU: Thiessen, M
EM: mthies1@lsu.edu
AF: Department of Geology & Geophysics, Louisiana State University, Baton Rouge, LA 70803,
AU: Aronowsky, A
EM: aaronows@hotmail.com
AF: Department of Geology & Geophysics, Louisiana State University, Baton Rouge, LA 70803,
AU: Anderson, L
EM: glande@lsu.edu
AF: Department of Geology & Geophysics, Louisiana State University, Baton Rouge, LA 70803,
AU: Bao, H
EM: bao@lsu.edu
AF: Department of Geology & Geophysics, Louisiana State University, Baton Rouge, LA 70803,
AU: Engel, A
EM: aengel@lsu.edu
AF: Department of Geology & Geophysics, Louisiana State University, Baton Rouge, LA 70803,
AB: Bacterial endosymbiosis is widespread among Bivalvia. Symbiosis between lucinid bivalves and sulfur-oxidizing (thiotrophic) bacteria has received recent attention, as lucinids are one of the geologically oldest extant bivalve clades to possess endosymbionts. However, the ecological and evolutionary relationships between host and symbiont are poorly understood, and reconstructing the evolutionary history and geological significance of lucinid endosymbiosis requires additional knowledge and characterization of endosymbiont ecology and taxonomic diversity. Our goal was to characterize the bacterial diversity of a modern lucinid habitat in order to evaluate possible lucinid endosymbiont diversity. Host organisms ( Lucinisca nassula and Phacoides pectinatus) and sediment cores were collected from geochemically reducing and sulfide-rich sea grass beds. PCR amplification and sequencing of bacterial 16S rRNA genes from the sediment cores retrieved 13 major taxonomic groups, including equally dominant Chloroflexi, Delta-, and Gammaproteobacteria, and rare Bacteroides, Acidobacteria, Spirochaetes, and Firmicutes. Less than 2% of the sequences were affiliated with uncultured gammaproteobacterial symbiont groups, but were not closely related to the sequences retrieved from the lucinid gills. Moreover, our analyses uncovered multiple gene sequence populations within an individual, as well as across individuals within the same sampling site. Additional habitat-host-symbiont diversity from three other lucinid taxa and from six geographically distinct habitat sites is also expanding the previously understood diversity of thiotrophic endosymbionts, and specifically that the lucinid symbionts are probably not a monophyletic species. These data suggest that thiotrophic bacteria are recruitable for endosymbiosis and are widely distributed in reducing marine environments. But, because of the diversity of bacteria in any one habitat, symbionts may be metabolically and physiologically diverse. An implication of this work is that the possible geochemical record of the lucinid-symbiont association may not yield systematic results.
DE: 0410 Biodiversity
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0448 Geomicrobiology
DE: 0460 Marine systems (4800)
DE: 0488 Sulfur cycling
SC: Biogeosciences [B]
MN: 2007 Fall Meeting