Formation physiology of xylanases by the grey series of Streptomyces

Abstract

Fifteen cultures belonging to the grey series of Streptomyces sp. were screened for their ability to utilize xylan as a sole carbon and energy source in a synthetic defined medium. Eleven cultures belonging to eleven species produced significant levels of extracellular xylanases in the medium under aerobic growth conditions. Physiological studies conducted on two cultures belonging to S. griseoflavus and S. violarus in a synthetic medium revealed that high level of xylanase activities are formed in the presence of different organic and inorganic nitrogen sources including lactose, galactose and mannose as well as xylan. The enzyme biosynthesis was favored in media with initial pH values around neutrality and reached its maximum levels after 3 to 4 days aerobic incubation at 30°C. Further studies have also revealed that both organisms could produce xylanase activities on lignocellulosic wastes including wheat bran, cane bagasse, wheat straw, rice husks and corn cubs. Using those agricultural byproducts at concentrations between 0.5–4% (w/v), both organisms could produce markedly higher levels of xylanase activities as compared with those formed purified xylan polymer. The results are discussed in the light of the production feasibility of this important group of enzymes from Streptomycetes.