Conclusion
The discovery of new microbial sources of cellulases is a crucial
strategy to reduce costs of various industrial processes using such
enzymes. Cellulases are produced by various microorganisms including
bacteria, fungi and actinomycetes. Recently was reported that they are
also produced by some animals like termites and crayfish without
certainties about his role in vivo 45. The
search, isolation and identification of new cellulose degrading
microorganisms from different environments are of crucial importance to
get new cellulases with unique and distinctive characteristics.
Microalgae are considered a valuable source of new enzymes with
biotechnological potential. However, the presence of cellulolytic
enzymes is meagre studied form this photosynthetic microorganisms.
Different works published during the last decade report cellulolytic
activity (either by experimental evidence or by bioinformatic analysis)
in C. reinhardtii , V. carteri , G. pectorale andA. protothecoides but the genus Scenedesmus had not been analysed3,5,46.
This is the first bioinformatic analysis of Scenedesmaceae cellulases
reported. It comprises GH5 and GH9 β-1,4-endoglucanases, GH1
β-glucosidases and GH10 exoglucanases. Our results shows that GH9
endoglucanases analyzed are phylogenetically closer to invertebrates,
termites and bivalve rather than higher plant, bacteria or fungi. On the
other hand, most of GH1 β-glucosidases analyzed are evolutionarily
closer to enzymes of other microalgae, however, four of them are grouped
in a branch close to the bacteria enzymes, result that suggests the
probable gaining of their genes by horizontal transfer. In contrast, GH5
and GH10 studied enzymes are evolutionarily closer to enzymes of other
microalgae and higher plants.
Most of the analyzed enzymes present signal peptides for membrane
anchoring or extracellular secretion. This result suggests the presence
of extracellular cellulolytic machinery in Scenedesmaceae. Only some of
the analyzed enzymes were found to have additional modules and linkers
besides its GH domains, and particularly a few endoglucanases have CBM
modules, from CBM1 and CBM2 families.
The combination of GH catalytic domains together with CBMs and, in some
cases linkers, propose that these cellulases would present an enhanced
cellulolytic activity.
The presence of this battery of enzymes in the photoheterotrophic algaeScenedesmus suggest that these organisms are perfectly prepared
for use of cellulose as carbon source. This strategy would represent an
advantage that would have allowed Scenedesmaceae to occupy many
environments in nature.
The findings reported in this work explores just one family within the
Chlorophyta taxon, but it increases the evidence in favor of the
presence of conserved cellulolytic machinery in photoheterotrophic
organisms and encourages to continue with the search for cellulases in
other species of microalgae.