<div>Lignocellulose is the most abundant natural biopolymer on earth and a
potential raw material for the production of fuels and chemicals.
However, only some organisms such as bacteria and fungi produce the
necessary enzymes to metabolize it. In this work we detected the
presence of extracellular cellulases in the genome of five species of
<i>Scenedesmus</i>. These microalgae grow in both, freshwater and
saltwater regions as well as in soils, displaying highly flexible
metabolic properties. The comparison of sequences of the different
cellulases with hydrolytic enzymes from other organisms by means of
multi-sequence alignments and phylogenetic trees showed that these
enzymes belong to the families of glycosyl hydrolases 1, 5, 9 and 10. In
addition, most of these presented a greater similarity of sequence with
enzymes from invertebrates, fungi, bacteria and other microalgae than
with cellulases from plants; and the 3D modeling data obtained showed
that both the main structures of the modeled proteins and the main amino
acid residues implicated in catalysis and substrate binding are well
conserved in <i>Scenedesmus</i> enzymes. We propose that these
cellulase-producing phototrophic microorganisms could act as catalysts
for the hydrolysis of cellulosic biomass fueled by sunlight.</div>