Production of several isoforms of β-1,4-glucanase by the cyanolichen Peltigera canina

Lichen cellulase may participate in the degradation of the external substrata and/or modification of the photobiont cell wall. To promote a better understanding of the roles of cellulases in lichens, a cyanolichen was chosen because of the absence of cellulose in its symbionts. Freshly-collected thalli of Peltigera canina (L.) Wild, produce β-1,4-glucanase (EC 3.2.1.4, β-1,4-D-glucanohydrolase). This enzyme's activity was detected in the soluble and cell wall fractions and it was found to be secreted to the incubation medium when thalli were floated on water or on cellobiose. Several forms of the enzyme were detected by isoelectrofocusing. In preparative isoelectrofocusing, a single peak was obtained in each fraction, characterized by pls of 5.05, 5.25 and 4.75 in the soluble, cell wall and medium fractions, respectively. These differences were in agreement with the different pattern of bands obtained in slab-isoelectrofocusing, where the most acidic band (pl of 4.45) was present only in the soluble fraction and the band with higher pl (6.17) was more intense in the cell wall fraction. Since both symbionts in a cyanolichen lack cellulose, cellulases cannot participate in the modification of their cell wall; the presence of cellulase in Peltigera canina must therefore be related to the degradation of the tissues of the moss substratum.