Published in Abstracts of American Society of Microbiology Annual General Meeting
2008
Ecology of Nitrogen Fixing Bacteria Associated with the coral Montipora capitata
Nathan Olson University of Hawaii at Hilo, Hilo, HI
Tracy Ainsworth University of Queensland, Queensland AUS
Ruth D. Gates Hawaiian Institute of Marine Biology, Kaneohe, HI
Misaki Takabayashi University of Hawaii at Hilo, Hilo, HI
Coral reef productivity, including that of endosymbiotic dinoflagellates in reef
invertebrates, has traditionally been viewed as nitrogen limited. However, the recent
discovery of nitrogen fixing bacteria associated with these corals directly contradicts this
view. The goal of this research project was to determine if nitrogen-fixing bacteria are
associated with Hawaiian corals and if found, to investigate the ecology of these bacteria.
Fragments of the coral Montipora capitata were collected from two sites; the east side of
the Island of Hawaii and from Kaneohe Bay on the Island of Oahu. The gene nifH was
isolated and sequenced from these samples. This gene codes for a subunit of nitrogenase,
the enzyme responsible for nitrogen fixation. nifH sequence analysis indicates these
sequences belong to bacteria that are closely related to Vibrio. Fluorescent in situ
hybridization using genetic probes specific to Vibrio revealed that these bacteria are
located within the coral’s epidermal tissue layer. Quantitative PCR was employed to
characterize the abundance of nitrogen-fixing bacteria within colonies of M. capitata in
correlation with mitotic index patterns of Symbiodinium, the symbiotic dinoflagellates.
Collectively, this research indicates the potential for a mutualistic endosymbiotic
relationship between the host coral M. capitata, Symbiodinium, and nitrogen-fixing
bacteria of the genus Vibrio.