Abstract
Mangrove sediments from New Caledonia were screened for xylanase sequences. One enzyme was selected and characterized both biochemically and for its industrial potential. Using a specific cDNA amplification method coupled with a MiSeq sequencing approach, the diversity of expressed genes encoding GH11 xylanases was investigated beneath Avicenia marina and Rhizophora stylosa trees during the wet and dry seasons and at two different sediment depths. GH11 xylanase diversity varied more according to tree species and season, than with respect to depth. One complete cDNA was selected (OFU29) and expressed in Pichia pastoris. The corresponding enzyme (called Xyn11-29) was biochemically characterized, revealing an optimal activity at 40–50 °C and at a pH of 5.5. Xyn11-29 was stable for 48 h at 35 °C, with a half-life of 1 h at 40 °C and in the pH range of 5.5–6. Xyn11-29 exhibited a high hydrolysis capacity on destarched wheat bran, with 40% and 16% of xylose and arabinose released after 24 h hydrolysis. Its activity on wheat straw was lower, with a release of 2.8% and 6.9% of xylose and arabinose, respectively. As the protein was isolated from mangrove sediments, the effect of sea salt on its activity was studied and discussed.
Highlights
This study revealed that the composition of secreted lignocellulolytic enzymes was strongly modified in the presence of sea salt, with increased secretion of xylanases and cellulases and lower production of oxidoreductases [8]
The diversity of expressed genes encoding fungal GH11 xylanases was investigated in surface and deeper mangrove sediments beneath A. marina (A) and R. stylosa (R) trees during the wet (March) and dry (November) seasons in three independent plots
The normalized GH11 xylanase dataset consisted of 247,464 sequences distributed among only 15 different operational functional units (OFUs) corresponding to 15 putative GH11 xylanase encoding cDNAs (Figure 1, Supplementary Table S2)
Summary
The mangrove is a unique ecosystem located at an interface between terrestrial, estuarine, and near-shore marine ecosystems. It is exposed to tides and has to live with high concentrations of salts due to the evaporation of saline water. Mangrove trees have developed unique adaptations to survive high levels of salinity either by excreting salts through their leaves or by excluding them at the root surface with a filtration system. One of the main environmental factors controlling the distribution of vegetation appears to be sediment salinity, which is partly controlled by the position of the stand in the intertidal
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