Laccase SilA from Streptomyces ipomoeae CECT 3341, a key enzyme for the degradation of lignin from agricultural residues?

Alba Blánquez,José Antonio González-Pérez,Francisco González-Vila,Manuel Hernández,Nicasio T Jiménez-Morillo,M Enriqueta Arias,Andrew S Ball,Marie-Joelle Virolle

doi:10.1371/journal.pone.0187649

Alba Blánquez, José Antonio González-Pérez + Show 6 more

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https://doi.org/10.1371/journal.pone.0187649

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Abstract

The role of laccase SilA produced by Streptomyces ipomoeae CECT 3341 in lignocellulose degradation was investigated. A comparison of the properties and activities of a laccase-negative mutant strain (SilA−) with that of the wild-type was studied in terms of their ability to degrade lignin from grass lignocellulose. The yields of solubilized lignin (acid precipitable polymeric lignin, APPL) obtained from wheat straw by both strains in Solid State Fermentation (SSF) conditions demonstrated the importance of SilA laccase in lignin degradation with the wild-type showing 5-fold more APPL produced compared with the mutant strain (SilA−). Analytical pyrolysis and FT-IR (Fourier Transform Infrared Spectroscopy) confirmed that the APPL obtained from the substrate fermented by wild-type strain was dominated by lignin derived methoxyphenols whereas those from SilA− and control APPLs were composed mainly of polysaccharides. This is the first report highlighting the role of this laccase in lignin degradation.

Highlights

Laccases are a group of multi-copper enzymes widely distributed in nature
The results showed the presence of a green halo around the colonies of the wild strain as a result of the oxidation of the ABTS by the studies a thermostable laccase (SilA) laccase but not in the mutant strain (Fig 1A-3)
It seems clear that bacterial laccases have a variety of functions, suggesting that these enzymes are functionally diverse and worthy of further research

Summary

Introduction

Laccases (benzenediol:oxygen oxidoreductase, EC 1.10.3.2) are a group of multi-copper enzymes widely distributed in nature. They have low specificity, and can oxidize a variety of phenolic and non-phenolic substrates, usually via mediators by coupling the oxidation of a substrate to the reduction of molecular oxygen to water [1]. The number of laccases already described is more limited than in fungi but some of them are of great interest because of their ability to retain their function under extreme conditions which are often required by the biotechnology industry. Bacteria exhibit higher growth rates than fungi and are more amenable to improvements in activity, selectivity and expression levels through protein engineering [2].

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