The metagenomic
analysis of gut microbiomes has emerged as a powerful strategy to identify
biomass-degrading enzymes, which will be no doubt useful for the development of
advanced biorefining processes.
In the present study,
we have performed a functional metagenomic analysis on nest and gut microbiomes
associated with the fungus growing termite Pseudacanthotermes
militaris [1].
Using whole termite
abdomens and fungal-comb material, two fosmid-based metagenomic libraries were
created and screened for the presence of xylan-degrading enzymes. We obtained
101 positive clones, corresponding to an extremely high global hit rate of
0.49%. Many clones displayed either β-D-xylosidase or α-L-arabinofuranosidase activity, while others displayed the ability to
degrade AZCL-xylan or AZCL-β-(1,3)-β-(1,4)-glucan. Using secondary screening, it was possible to pinpoint interesting
clones that were sequenced. Bioinformatics analysis of the resultant 1.46 Mbp DNA
revealed 63 sequences, encoding putative carbohydrate-active enzymes, with many
of these forming parts of sequence clusters, probably having carbohydrate
degradation functions.
Taxonomic assignment
revealed the dominant phyla in the abdomen and the comb samples. These results show
that not only the gut microbiome of P. militaris possesses the potential
to degrade biomass components, but that the prokaryotic microbal community in
the nest could also play a part in the degradation of biomass within the
termite mound.
From an enzyme
discovery point of view, this study has provided a collection of interesting
biocatalysts for further study. Recombinant expression in E. coli of selected
gene candidates has provided access to individual enzyme activities, which have
all proved to be coherent with the primary and secondary functional screens.
Acknowledgement : Funding for this project was supplied by grants from Midi-Pyrénées regional authorities and OSEO.
[1] Bastien G, Arnal
G, Bozonnet S, Laguerre S, Ferreira F, Fauré R, Henrissat B , Lefèvre F, Robe
P, Bouchez O, Noirot C, Dumon C, O’Donohue M.
Biotechnol. Biofuels, in press.
