Production of extracellular enzymes by Thermomonospora curvata during growth on protein‐extracted lucerne fibres

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Abstract
After extraction of food protein from lucerne, the residual fibre was used as a carbon and energy source by the thermophilic actinomycete, Thermomonospora curvata. Induction of catabolic exoenzymes during growth for 7 d on the fibre at 53°C in a mineral salts minimal medium was compared with that on a variety of other inductive substrates. A fibre concentration of 1.5% (w/v) was optimal for total protein secretion. The fibre was a poor substrate for amylase production due to lack of inducer rather than to catabolite repression by soluble sugars released during degradation. β‐Glucosidase release during growth on the fibre was about 10 times that observed in cultures grown on cellobiose or cellulose, but production of other cellulolytic enzymes was about one‐half that produced on cellulose. Pectinolytic activity (measured as polygalacturonate lyase) was equal to that produced on pectin. Cells grown on the fibre released about eight times as much proteinase as those grown on cellulose, but proteolytic activity was transient and decreased rapidly during later growth. Xylanase appeared to be co‐ordinately induced with cellulolytic enzymes; comparable maximal activities, observed during growth on either the fibre or cellulose, were three times that produced on xylan or xylose.