Microbial Interactions Associated with Biofilms Attached to Trichodesmium spp. and Detrital Particles in the Ocean

Quorum sensing (QS) via acylated homoserine lactones (AHLs) was discovered in the ocean, yet little is known about its role in the ocean. The objectives of this thesis were to constrain the chemical stability of AHLs, their occurrence in marine particulate environments and the behaviors they might regulate in the ocean. In this dissertation I established that AHLs are more stable in seawater than expected and are likely to accumulate within biofilms. Using culture dependent and independent-techniques, I established that Trichodesmium colonies host biofilm communities distinct from seawater. Using HPLC-MS I determined that bacteria isolated from biofilms attached to Trichodesmium synthesize AHLs and that AHLs are also present in sinking POC collected near Vancouver Island, Canada. This was the first time AHLs have been detected in POC and their presence indicated that AHL-QS was occurring in the POC sample. We also showed that AHLs enhanced the activity of hydrolytic enzymes in a non-axenic Trichodesmium culture and in sinking POC. My results suggest AHL-QS is a factor regulating biogeochemically relevant enzyme activities on sinking POC and within the biofilms attached to Trichodesmium colonies and thereby may impact the timing and magnitude of biogeochemical fluxes in the ocean. The original document contains color images.