DISCERNING THE MECHANISMS OF COEXISTENCE BETWEEN MARINE CREN/THAUMARCHAEA AND MARINE BACTERIA VIA STABLE ISOTOPE PROBING DISCERNING THE MECHANISMS OF COEXISTENCE BETWEEN MARINE CREN/THAUMARCHAEA AND MARINE BACTERIA VIA STABLE ISOTOPE PROBING

Lauren Seyler, Lauren Seyler, Lee Kerkhof
unpublished
Marine mesophilic archaea were discovered two decades ago. However, the role of these culture-resistant organisms in marine nutrient cycling and the nature of their relationship with bacteria have yet to be elucidated. Current thinking is that thaumarchaea may dominate ammonia oxidation in sediments and oxygen minimum zones, based on the ubiquity of archaeal ammmonium monooxygenase genes. Yet, ammonia-oxidation (or other forms of autotrophy/mixotrophy) may only represent a subset of the full
more » ... bset of the full metabolic capability of the phylum. The purpose of this Ph.D. research was to assess whether estuary and marine archaea are autotrophic or heterotrophic and if they compete with bacteria for the same electron donors and acceptors. Salt marsh sediments from a New Jersey state park were screened for heterotrophy using stable isotope probing, by amending with a single 13 C-labeled compound (acetate, glycine, or urea), a complex 13 C-biopolymer (lipids, proteins, or growth medium), or autotrophy using 13 C-bicarbonate. ii 13 C-labeled DNA was analyzed by TRFLP analysis of 16S rRNA genes. SIP analyses indicated salt marsh thaumarchaea and crenarchaea are heterotrophic, double within 2-3 days and often compete with heterotrophic bacteria for the same organic substrates. A clone library of 13 C-amplicons was screened to find matches to the 13 C-TRFLP peaks. Some of these archaea displayed a preference for particular carbon sources, whereas others incorporated nearly every 13 C-substrate provided. Resource partitioning of proteins, and urea at low concentrations, was also observed. SIP was also performed in the open waters of the Sargasso Sea at multiple depths and latitudes, using 13 C-labeled acetate, urea, and bicarbonate. In this environment, mixotrophy appeared to be the dominant metabolic strategy, though some heterotrophic OTUs (operational taxonomic units) were observed. No exclusively autotrophic OTUs were detected. Urea was also a competitive substrate in deep waters, with archaea outcompeting bacteria for its uptake in the majority of microcosms. Archaea-specific and bacteria-specific predators were detected via incorporation of 13 C into eukaryotic OTUs. This research demonstrates the significance of organic carbon uptake and selective predation on the structuring of marine archaeal communities. iii ACKNOWLEDGEMENTS
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