الفهرس 
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Abstract
The recent concerns in regard to global climate change and the need for renewable and sustainable source of liquid fuel has become one of the most challenging issues in the 21st century. Therefore the interest has been focused recently on the use of non-food plant products, mainly lignocellulose as industrial raw materials for the production of a second-generation biofuel, cellulosic ethanol.
Several fungi and bacteria are capable to degrade lignocellulose. Actinomycetes are characterized by their wide spread in different habitats in nature at moderate and high temperatures. Actinomycetes, particularly members of the genus Streptomyces, produce extracellular ligninolytic, cellulolytic and hemicellulolytic enzymes to degrade lignocellulosic materials
In this study, thermophilic actinomycetes were isolated from agricultural residues compost located at the Faculty of Agriculture, Minia University. The isolated actinomycetes were able to utilize xylan (avicel or breach wood xylan) as the sole carbon source
Five morphologically distinct, xylan degrading actinomycetes that grew on xylan were recorded, selected and qualitatively tested for their xylanolytic activity by using Congo red clearing zone assay. Their quantitative xylanase production was estimated by measuring the reducing sugars content in the culture filtrate. MN3 isolate exhibited the highest xylanolytic activity and was able to degrade agricultural waste (wheat straw, rice straw and bagasse) as a sole carbon source releasing reducing sugars, the highest activity was detected on rice straw.
The highest xylanase production was obtained in the thermophilic range at 45oC, pH 8.0, after 7 days of incubation. The highest xylanase activity was obtained at 65oC indicating the thermophilic nature of this enzyme at pH range from pH 6.0 to pH 8.0 after 50 minutes of incubation.
The isolated actinomycete was genomically identified by 16S rRNA gene sequence determination, its similarity to known sequences of the 16S ribosomal RNA for bacteria and archaea was determined through BLAST database at the National Centre for Biotechnology Information (NCBI - https://www.ncbi.nlm.nih.gov). 16S rDNA gene sequence analysis did not give an exact species level identification for the isolated Streptomyces sp. MN3 isolate.
Phenotypic classification of Streptomyces sp. MN3 isolate according to the International Streptomyces Project (ISP) indicated that it has a strong similarity to four Streptomyces species (S.eurythermus, S. griseosporeus, S. rishiriensis and S. aurantiogriseus). According the phenotypic characterization and other criteria, the isolated Streptomyces sp. MN3 was identified to be a strain of Streptomyces eurythermus.
Two endoxylanase encoding genes, SCO0674 and SCO2292, were identified in the genome of Streptomyces coelicolor (A3) (has a complete genome sequence). SCO0674 is 1260 bp long gene that encodes a GH10 endoxylanase, whereas SCO2292 is 1008 bp long gene that encodes a GH11 endoxylananse. They were cloned into the expression vector pET47b (+) using EcoRI and HindIII endonucleases. Induction to their expression in E. coli BL21 (DE3) was failed; mostly an expression in Streptomyces itself is needed, since many cloned Streptomyces genes were successfully induced in Streptomyces lividans as expression host.