AUTHOR=Ventorino Valeria , Ionata Elena , Birolo Leila , Montella Salvatore , Marcolongo Loredana , de Chiaro Addolorata , Espresso Francesco , Faraco Vincenza , Pepe Olimpia 

TITLE=Lignocellulose-Adapted Endo-Cellulase Producing Streptomyces Strains for Bioconversion of Cellulose-Based Materials

JOURNAL=Frontiers in Microbiology

VOLUME=7

YEAR=2016

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2016.02061

DOI=10.3389/fmicb.2016.02061

ISSN=1664-302X

ABSTRACT=<p>Twenty-four <italic>Actinobacteria</italic> strains, isolated from <italic>Arundo donax, Eucalyptus camaldulensis</italic> and <italic>Populus nigra</italic> biomass during natural biodegradation and with potential enzymatic activities specific for the degradation of lignocellulosic materials, were identified by a polyphasic approach. All strains belonged to the genus <italic>Streptomyces</italic> (<italic>S</italic>.) and in particular, the most highly represented species was <italic>Streptomyces argenteolus</italic> representing 50% of strains, while 8 strains were identified as <italic>Streptomyces flavogriseus</italic> (synonym <italic>S. flavovirens</italic>) and <italic>Streptomyces fimicarius</italic> (synonyms <italic>Streptomyces acrimycini, Streptomyces baarnensis, Streptomyces caviscabies</italic>, and <italic>Streptomyces flavofuscus</italic>), and the other four strains belonged to the species <italic>Streptomyces drozdowiczii, Streptomyces rubrogriseus, Streptomyces albolongus</italic>, and <italic>Streptomyces ambofaciens</italic>. Moreover, all <italic>Streptomyces</italic> strains, tested for endo and exo-cellulase, cellobiase, xylanase, pectinase, ligninase, peroxidase, and laccase activities using qualitative and semi-quantitative methods on solid growth medium, exhibited multiple enzymatic activities (from three to six). The 24 strains were further screened for endo-cellulase activity in liquid growth medium and the four best endo-cellulase producers (<italic>S. argenteolus</italic> AE58P, <italic>S. argenteolus</italic> AE710A, <italic>S. argenteolus</italic> AE82P, and <italic>S. argenteolus</italic> AP51A) were subjected to partial characterization and their enzymatic crude extracts adopted to perform saccharification experiments on <italic>A. donax</italic> pretreated biomass. The degree of cellulose and xylan hydrolysis was evaluated by determining the kinetics of glucose and xylose release during 72 h incubation at 50°C from the pretreated biomass in the presence of cellulose degrading enzymes (cellulase and β-glucosidase) and xylan related activities (xylanase and β-xylosidase). The experiments were carried out utilizing the endo-cellulase activities from the selected <italic>S. argenteolus</italic> strains supplemented with commercial β-gucosidase and xylanase preparations from Genencore (Accellerase BG and Accellerase XY). Cellulose and xylan conversion, when conducted using commercial (hemi)cellulases, gave glucose and xylose yields of 30.17 and 68.9%, respectively. The replacement of the cellulolytic preparation from Genencor (Accellerase 1500), with the endo-cellulase from <italic>S. argenteolus</italic> AE58P resulted in almost 76% of the glucose yield obtained in the presence of the commercial counterpart. Due to the promising results obtained by using the enzymatic crude extracts from <italic>S. argenteolus</italic> AE58P in the pretreated <italic>A. donax</italic> saccharification experiments, the proteins putatively responsible for endo-cellulase activity in this strain were identified by proteomics. Several proteins were confidently identified in different <italic>Streptomyces</italic> spp., eight of which belong to the class of Carbohydrate active enzymes. Overall results highlighted the biotechnological potential of <italic>S. argenteolus</italic> AE58P being an interesting candidate biocatalyst-producing bacterium for lignocellulose conversion and production of biochemicals and bioenergy.</p>