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 beyond its involvement in certain symbiotic interactions. The objectives of this thesis were to constrain the chemical stability of AHLs in seawater, explore the production of AHLs in marine particulate environments, and probe selected behaviors which might be controlled by AHL-QS. I established that AHLs are more stable in seawater than previously expected and are likely to accumulate within biofilms. Based on this result, I chose to study AHLQS in the bacterial communities inhabiting biofilms attached to Trichodesmium spp. and detrital (photosynthetically-derived sinking particulate organic carbon, POC) particles. These hot spots of microbial activity are primary sites of interaction between marine primary producers and heterotrophs and crucial components of the biological pump. Biofilm communities associated with Trichodesmium thiebautii colonies in the Sargasso Sea differed considerably from seawater microbial communities. In addition, there was no overlap between the communities associated with tuft and puff colonies. These results suggest that bacterial communities associated with Trichodesmium are not random; rather, Trichodesmium selects for specific microbial flora. Novel 16S rRNA gene sequences are present both in clone libraries constructed from DNA extracted from colonies of Trichodesmium spp. and in culture collections derived from wild and laboratory cultivated Trichodesmium spp., supporting the idea that the phycosphere of Trichodesmium is a unique microenvironment. Using high performance liquid chromatography-mass spectrometry, I demonstrated that bacteria isolated from Trichodesmium synthesize AHLs. In addition, I detected AHLs in sinking particles collected from a site off of Vancouver Island, Canada. AHLs were subsequently added to laboratory cultures of non-axenic Trichodesmium colonies and sinking POC samples. This is the first time AHLs have been detected in POC and indicates that AHL-QS was occurring in POC. Further, I showed that AHLs enhanced certain organic-matter degrading hydrolytic enzyme activities. My results suggest that 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.

Department dc:contributor.department

Joint Program in Oceanography/Applied Ocean Science and Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2010

Author dc:creator

• Hmelo, Laura Robin

Advisor dc:contributor.advisor

• Benjamin A.S. Van Mooy.

• Joint Program in Oceanography/Applied Ocean Science and Engineering.
• Earth, Atmospheric, and Planetary Sciences.
• Woods Hole Oceanographic Institution.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/59739

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/59739