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A pseudorandom genomic library of Bacteroides succinogenes DNA, cloned into pUC8 in Escherichia coli, was screened for beta-glucanase activity on 0.1% lichenan plates. Six high-activity clones, containing identical 5.2-kilobase inserts of B. succinogenes DNA, were obtained. The clones exhibited activity solely on beta-glucan substrates containing beta-(1----3)(1----4) linkages, thus manifesting a specific fibrolytic enzyme previously unrecognized in B. succinogenes. A subclone (pJI10) of the original insert (1.35 kilobases in size) expressed full beta-glucanase activity under control of its own promoter. The expression of beta-glucanase in pJI10 appeared subject to catabolite regulation by glucose. Detailed analysis of enzyme activity in the parental and deleted derivatives, subcloned into pUC18 and pUC19, suggested that the apparent glucose repression was an artifact arising as a consequence of interactions with the lac transcriptional unit in the plasmid vector.

A 1,3-1,4-beta-D-glucanase (lichenase, 1,3-1,4-beta-D-glucan 4-glucanohydrolase, EC 3.2.1.73) from Bacteroides succinogenes cloned in Escherichia coli was purified 600-fold by chromatography on Q-Sepharose and hydroxyapatite. The cloned enzyme hydrolysed lichenin and oat beta-D-glucan but not starch, CM(carboxymethyl)-cellulose, CM-pachyman, laminarin or xylan. The enzyme had a broad pH optimum with maximum activity at approx. pH 6.0 and a temperature optimum of 50 degrees C. The pH of elution from a chromatofocusing column for the cloned enzyme was 4.7 (purified) and 4.9 (crude) compared with 4.8 for the mixed-linkage beta-D-glucanase activity in B. succinogenes. The Mr of the cloned enzyme was estimated to be 37,200 by gel filtration and 35,200 by electrophoresis. The Km values estimated for lichenin and oat beta-D-glucan were 0.35 and 0.71 mg/ml respectively. The major hydrolytic products with lichenin as substrate were a trisaccharide (82%) and a pentasaccharide (9.5%). Hydrolysis of oat beta-D-glucan yielded a trisaccharide (63.5%) and a tetrasaccharide (29.6%) as the major products. The chromatographic patterns of the products from the cloned enzyme appear to be similar to those reported for the mixed-linkage beta-D-glucanase isolated from Bacillus subtilis. The data presented illustrate the similarity in properties of the cloned mixed-linkage enzyme and the 1,3-1,4-beta-D-glucanase from B. subtilis and the similarity with the 1,4-beta-glucanase in B. succinogenes.