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Molecular Ecological and Stable Isotopic Studies of Nitrogen Fixation in Modern Microbial MatsNitrogen is usually the element limiting biological productivity in the marine environment. Microbial mats, laminated microbial communities analogous to some of the oldest forms of life on Earth, are often the sites of high rates of N fixation (the energetically expensive conversion of atmospheric dinitrogen into a biologically useful form). The N fixing enzyme nitrogenase is generally considered to be of ancient origin, and is widely distributed throughout the Bacterial and Archaeal domains of life, indicating an important role for this process over evolutionary time. The stable isotopic signature of N fixation is purportedly recognizable in organic matter (ancient kerogens as well as present-day microbial mats) as a delta (15)N(sub organic) near zero. We studied two microbial mats exhibiting different rates of N fixation in order to better understand the impact of N fixation on the delta (15)N (sub organic) of the mats, as well as what organisms are important in this process. Mats dominated by the cyanobacterium Microcoleus chthonoplastes grow in permanently submerged hypersaline salterns, and exhibit low rates of N fixation, whereas mats dominated by the cyanobacterium Lyngbya spp grow in an intertidal area, and exhibit rates of N fixation an order of magnitude higher. To examine successional stages in mat growth, both developing and established mats at each location were sampled. PCR and RT-PCR based approaches were used to identify, respectively, the organisms containing nifH (one of the genes that encode nitrogenase) as well as those expressing nifH in these mats. Both mats exhibited a distinct diel cycle of N fixation, with highest rates occurring at night. The delta (15)N(sub organic) of the subtidal Microcoleus mats is near zero whereas the delta (15)N(sub organic) is slightly more positive (+ 2-3%), in the intertidal Lyngbya mats, an interesting difference in view of the fact that overall rates of activity in the intertidal mats are much higher that those in the submerged hypersaline mats. Developing mats in both the subtidal and intertidal locations had delta (15)N(sub organic) values very near those of the established mats. Further work is necessary in order to determine the importance of other transformations of nitrogen on the delta (15)N(sub organic) signature of the mats.
Document ID
20040081229
Acquisition Source
Ames Research Center
Document Type
Conference Paper
Authors
Bebout, B. M.
(NASA Ames Research Center Moffett Field, CA, United States)
Crumbliss, L. L.
(California Univ. Santa Cruz, CA, United States)
DesMarais, D. J.
(NASA Ames Research Center Moffett Field, CA, United States)
Hogan, M. E.
(NASA Ames Research Center Moffett Field, CA, United States)
Omoregie, E.
(California Univ. Santa Cruz, CA, United States)
Turk, K. A.
(NASA Ames Research Center Moffett Field, CA, United States)
Zehr, J. P.
(California Univ. Santa Cruz, CA, United States)
Date Acquired
August 21, 2013
Publication Date
August 6, 2003
Subject Category
Life Sciences (General)
Meeting Information
Meeting: Presentation: Exobiology P.I. Symposium
Location: Moffett Field, CA
Country: United States
Start Date: August 25, 2003
End Date: August 29, 2003
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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