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Applied and Environmental Microbiology, June 2006, p. 4184-4191, Vol. 72, No. 6
0099-2240/06/$08.00+0     doi:10.1128/AEM.02882-05
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Dynamics and Characterization of Refractory Dissolved Organic Matter Produced by a Pure Bacterial Culture in an Experimental Predator-Prey System

David F. Gruber,1,{dagger} Jean-Paul Simjouw,1,{dagger}* Sybil P. Seitzinger,1,2 and Gary L. Taghon1

Institute of Marine and Coastal Sciences,1 CMER Program, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 089012

Received 7 December 2005/ Accepted 4 April 2006

We studied the effects of a bacterium (Pseudomonas chlororaphis) and a bactivorous protozoan (Uronema sp.) on transformations of labile dissolved organic carbon (DOC). In 36-day time series experiments, bacteria were grown on glucose both with and without protozoa. We measured bulk organic carbon pools and used electrospray ionization mass spectrometry to characterize dissolved organic matter on a molecular level. Bacteria rapidly utilized glucose, depleting it to nondetectable levels and producing new DOC compounds of higher molecular weight within 2 days. Some of these new compounds, representing 3 to 5% of the initial glucose-C, were refractory and persisted for over a month. Other new compounds were produced and subsequently used by bacteria during the lag and exponential growth phases, pointing to a dynamic cycling of organic compounds. Grazers caused a temporary spike in the DOC concentration consisting of labile compounds subsequently utilized by the bacteria. Grazing did not increase the complexity of the DOC pool already established by the bacteria but did continually decrease the particulate organic carbon pool and expedited the conversion of glucose-C to CO2. After 36 days, 29% of initial glucose-C remained in pure bacteria cultures, while only 6% remained in cultures where a grazer was present. In this study the bacteria were the primary shapers of the complex DOC continuum, suggesting higher trophic levels possibly have less of an impact on the qualitative composition of DOC than previously assumed.

* Corresponding author. Mailing address: Institute of Marine and Coastal Sciences, Rutgers, The State University of New Jersey, 71 Dudley Rd., New Brunswick, NJ 08901. Phone: (732) 932-6555. Fax: (732) 932-1792. E-mail: simjouw{at}marine.rutgers.edu.

{dagger} D.F. Gruber and J.-P. Simjouw contributed equally to this work.

Applied and Environmental Microbiology, June 2006, p. 4184-4191, Vol. 72, No. 6
0099-2240/06/$08.00+0     doi:10.1128/AEM.02882-05
Copyright © 2006, American Society for Microbiology. All Rights Reserved.





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