On the basis of microscopic studies it is established that an abundant and diverse protistan community occurs in the oxygen-depleted, sulfide-enriched deep-sea sediments of the Santa Barbara Basin (SBB). The majority of these eukaryotes, many of which belong to taxa that are new to science, harbor prokaryotes in a putative symbiotic association. At present, the identity and physiological role/metabolic activities of these associated prokaryotes are unknown. The goal of this project is to investigate four specific prokaryote-eukaryote associations (putative symbioses) that were observed in SBB during previous studies by elucidating the host-symbiont identities and functions of these associations using a combination of culture-based, molecular, cell biological, and geochemical methods. These approaches include analyses of rRNA and functional genes, fluorescent in situ hybridization studies targeting rRNA (FISH), a combination of molecular identification and microautoradiography (MAR-FISH), and microscopical analyses (SEM, TEM). Material will be collected on two 5-day oceanographic cruises. The specific associations to be analyzed involve the following hosts: Calkinsia aureus (flagellate with ectobionts), Euglenoid sp. (flagellate with ectobionts), Metopus verrucosus (ciliate with ectobionts), and Metopus halophila or Parablepharisma sp. (ciliates with endobionts or ectobionts). These putative endo- and ectosymbionts are hypothesized to have a variety of metabolic capabilities.
This project will significantly enhance our knowledge of prokaryote-eukaryote associations in a poorly studied marine habitat. The majority of the SBB eukaryotes, many of which are yet to be described, have associations with prokaryotes that appear to be putative symbionts. The physiology, systematics, and metabolism of these associated prokaryotes are unknown. Elucidating the symbiotic relationships between prokaryotes and eukaryotes within the microbial community in this sulfidic and micro-oxic/anoxic deep-sea environment will shed light on the role that symbioses play within microbial consortia in their adaptation to these environments, and their potential impact on the biogeochemistry of that environment. Further, symbioses are potential vehicles for evolutionary change through the introduction of new genetic material, and therefore represent possible mechanisms of speciation. Symbioses may also allow for niche and habitat expansion, possibly a major factor in the early evolution and diversification of eukaryotes. This project will include active involvement of undergraduate and graduate students, K-12 teachers, and the lay public, as well as broad dissemination of results via internet-based knowledge networks, publications in widely-circulated professional scientific journals, educational activities (e.g., workshops for both secondary school teachers and research scientists), and seminars.