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Metabolic streamlining in an open-ocean nitrogen-fixing cyanobacterium
Tripp, H.J.; Bench, S.R.; Turk, K.A.; Foster, R.A.; Desany, B.A.; Niazi, F.; Affourtit, J.P.; Zehr, J.P. (2010). Metabolic streamlining in an open-ocean nitrogen-fixing cyanobacterium. Nature (Lond.) 464(7285): 90-94. https://hdl.handle.net/10.1038/nature08786
In: Nature: International Weekly Journal of Science. Nature Publishing Group: London. ISSN 0028-0836, more
Peer reviewed article  

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Keyword
    Marine

Authors  Top 
  • Tripp, H.J.
  • Bench, S.R.
  • Turk, K.A.
  • Foster, R.A.
  • Desany, B.A.
  • Niazi, F.
  • Affourtit, J.P.
  • Zehr, J.P.

Abstract
    Nitrogen (N(2))-fixing marine cyanobacteria are an important source of fixed inorganic nitrogen that supports oceanic primary productivity and carbon dioxide removal from the atmosphere(1). A globally distributed(2,3), periodically abundant(4) N(2)-fixing(5) marine cyanobacterium, UCYN-A, was recently found to lack the oxygen-producing photosystem II complex(6) of the photosynthetic apparatus, indicating a novel metabolism, but remains uncultivated. Here we show, from metabolic reconstructions inferred from the assembly of the complete UCYN-A genome using massively parallel pyro-sequencing of paired-end reads, that UCYN-A has a photofermentative metabolism and is dependent on other organisms for essential compounds. We found that UCYN-A lacks a number of major metabolic pathways including the tricarboxylic acid cycle, but retains sufficient electron transport capacity to generate energy and reducing power from light. Unexpectedly, UCYN-A has a reduced genome (1.44 megabases) that is structurally similar to many chloroplasts and some bacteria, in that it contains inverted repeats of ribosomal RNA operons(7). The lack of biosynthetic pathways for several amino acids and purines suggests that this organism depends on other organisms, either in close association or in symbiosis, for critical nutrients. However, size fractionation experiments using natural populations have so far not provided evidence of a symbiotic association with another microorganism. The UCYN-A cyanobacterium is a paradox in evolution and adaptation to the marine environment, and is an example of the tight metabolic coupling between microorganisms in oligotrophic oceanic microbial communities.

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