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Applied and Environmental Microbiology, November 1999, p. 4926-4934, Vol. 65, No. 11
The Institute of Physical and Chemical Research (RIKEN) and
Japan Science and Technology Corporation (JST),
Received 12 July 1999/Accepted 27 August 1999
Nitrogen fixation by the microorganisms in the gut of termites is
one of the crucial aspects of symbiosis, since termites usually thrive
on a nitrogen-poor diet. The phylogenetic diversity of the
nitrogen-fixing organisms within the symbiotic community in the guts of
various termite species was investigated without culturing the resident
microorganisms. A portion of the dinitrogenase reductase gene
(nifH) was directly amplified from DNA extracted from the
mixed population in the termite gut. Analysis of deduced amino acid
sequences of the products of the clonally isolated nifH
genes revealed the presence of diverse nifH sequences in most of the individual termite species, and their constituents were
considerably different among termite species. A majority of the
nifH sequences from six lower termites, which showed
significant levels of nitrogen fixation activity, could be assigned to
either the anaerobic nif group (consisting of clostridia
and sulfur reducers) or the alternative nif methanogen
group among the nifH phylogenetic groups. In the case of
three higher termites, which showed only low levels of nitrogen
fixation activity, a large number of the sequences were assigned to the
most divergent nif group, probably functioning in some
process other than nitrogen fixation and being derived from
methanogenic archaea. The nifH groups detected were similar
within each termite family but different among the termite families,
suggesting an evolutionary trend reflecting the diazotrophic habitats
in the symbiotic community. Within these phylogenetic groups, the
sequences from the termites formed lineages distinct from those
previously recognized in studies using classical microbiological techniques, and several sequence clusters unique to termites were found. The results indicate the presence of diverse potentially nitrogen-fixing microbial assemblages in the guts of termites, and the
majority of them are as yet uncharacterized.
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Phylogenetic Diversity of Nitrogen Fixation Genes
in the Symbiotic Microbial Community in the Gut of Diverse
Termites
*
Corresponding author. Mailing address: Microbiology
Laboratory, RIKEN (The Institute of Physical and Chemical Research),
Hirosawa 2-1, Wako, Saitama 351-0198, Japan. Phone: 81-48-462-1111, ext. 5724. Fax: 81-48-462-4672. E-mail:
mohkuma{at}mailman.riken.go.jp.
Applied and Environmental Microbiology, November 1999, p. 4926-4934, Vol. 65, No. 11
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
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