In our earlier work, we demonstrated that the oxidases tyrosinase and laccase occur widely in lichens from the Peltigerales. Recently, we discovered the occurrence of another oxidoreductase, a heme peroxidase, in the Peltigeralean ‘jelly lichens’ Leptogium and Collema. Here we present the results of a survey of peroxidase activity in a range of lichens. In addition to the jelly lichens, strong peroxidase activity also occurs within the Peltigeralean genera Lobaria, Pseudocyphellaria and Sticta. Significant activity occurs in the cell wall, and, unlike laccase activity, peroxidase activity increases considerably following the rehydration of dry thalli. However, activity is absent from Peltigera and from the non-Peltigeralean species tested here. Electrophoretic investigation showed that lichen peroxidases are oligomeric. Possible roles for peroxidases in lichen biology are discussed.

Bedouin goats were fed on wheat straw as a single-component diet under two watering regimens, drinking once daily or once every 4 d, in order to clarify whether lignin-degradation products were absorbed, metabolized and excreted in urine. Acid-soluble lignin accounted for 220 g/kg total lignin, its digestibility was the highest (0.87) and was unaffected by water deprivation. Acid-insoluble lignin accounted for 780 g/kg total lignin and its digestibility increased during water deprivation from 0.21 to 0.41. Alkali-soluble lignin accounted for 320 g/kg total lignin and its digestibility increased during water deprivation from 0.44 to 0.53. Digestibility of structural carbohydrate was considerably higher than that observed in other domesticated ruminants fed on wheat straw. It responded positively to water deprivation, increasing from 0.63 to 0.73 with cellulose and from 0.61 to 0.68 with hemicellulose. The amount of urinary aromatic acids, mainly in the form of hippuric acid, considerably exceeded the potential contribution of any non-lignin component which might affect the excretion of aromatic acids. A considerable percentage (71−76) of the apparently digested lignin was not accounted for as soluble phenolic compounds in faeces or as aromatic acids in urine, and hence was apparently completely metabolized. Lignin is a key substrate which is extensively digested in goats fed on low-quality forage, with subsequent absorption of end-products. This enhanced the availability of structural carbohydrates for fermentation and was associated with excretion of high-energy metabolites in the form of benzoic and hippuric acids.