APPENDIX VIII

MOLECULAR CHARACTERIZATION AND REGULATION OF AMMONIA ASSIMILATION IN CHEMOAUTOTROPHIC PROKARYOTE-EUKARYOTE SYMBIOSES

ONR NOOOI 4-91 -J-1 489
NSF OCE - 9504257

Principal Investigator: Colleen M. Cavanaugh
Postdoctoral Fellow: Raymond Lee

Objectives

• Determine pathways and mechanisms of organic nitrogen synthesis by deep-sea hydrothermal vent communities
• Assess the influence of geochemical processes on the capacity for organic nitrogen synthesis.

Approach

• Characterize nitrogen assimilation pathways in vent symbioses by enzyme activity measurements and DNA and immunoblot analyses.

Results

• Activities of key enzymes (glutamine synthetase (GS), glutamate dehydrogenase (GDH), and nitrate reductase (NR)) involved in ammonia and nitrate assimilation by free-living bacteria and other autotrophic organisms are present in vent symbioses.
• Differences between species in capacity for symbiont-based sulfur-oxidation and
• carbon fixation correlate with activities of GS, GDH, and NR.
• Based on Southern hybridizations and immunological detection, symbiont GS of all vent symbioses tested is a dodecameric type I form found in many species of freeliving bacteria.
• The capacity for nitrogen assimilation in the vent tubeworm, Riftia pachyptila, is affected strongly by proximity to active venting. Worms collected at a low temperature site exhibited a drastic reduction in NR activity, GS activity in host tissue, and symbiont GS protein.