Aquatic Sciences Meeting, Albuquerque 2001

PC04 Microbial Diversity

Date: Tuesday, February 13, 2001

Location: Southwest Hall

Hullar, M, A, Harvard University, Cambridge, USA, mhullar@oeb.harvard.edu

Cavanaugh, C, M, Harvard University, Cambridge, USA, cavanaug@fas.harvard.edu

Peterson, B, J, Marine Biological Laboratory, Woods Hole, USA, peterson@mbl.edu

NITROGEN AND CARBON ASSIMILATION BY ESTUARINE BACTERIA:MOLECULAR AND STABLE ISOTOPIC EVIDENCE FOR CHANGES IN BACTERIAL COMMUNITY STRUCTURE

To trace major pathways of nitrogen and carbon transformation in the microbial loop, stable isotope analyses of bacterial nucleic acids and bacterial community analysis, using PCR amplification of the 16S rRNA gene with Eubacteria primers and DGGE, were combined with a whole system 15N-nitrate isotope tracer addition in the oligohaline reach of the Parker River, MA estuary. Initial stable nitrogen isotope ratios of nucleic acids extracted from bacterial sized particles (BSP; <0.8µm->0.2µm) and particulate organic nitrogen (PON) averaged 7 ‰. After two weeks, nitrogen values in the BSP stabilized around 20 ‰. PO15N values continued to become heavier, reaching 60 ‰, reflecting nitrate incorporation by the diatom fraction. In contrast, natural abundance stable carbon isotope values of both the bacterioplankton and diatoms became similarly enriched suggesting bacterioplankton metabolize carbon derived from diatoms. This shift correlated with the appearance of two new ribotypes possibly associated with selection for physiological specialists within the bacterial community. Thus it appears bacteria in the oligohaline reach of the estuary consume carbon derived from phytoplankton but use other sources, in addition to nitrate, for nitrogen metabolism.

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Aquatic Sciences Meeting, Albuquerque 2001

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