Antimicrobial properties of three liverworts in axenic culture: Blasia pusilla, Pallavicinia lyellii and Radula obconica

Many liverworts have been reported to deter the growth of pathogenic agents such as fungi and bacteria. It has been generally assumed that the chemicals liverworts produce in their oil bodies are responsible for this activity. However, most of these studies have used plants from nature, and only a few of them have isolated and identified the specific compounds that are biologically active. This study aims to expand existing knowledge of biological activity of liverworts as follows: 1) testing whether plants raised in axenic culture display antimicrobial activity, 2) determining if antimicrobial activity can occur in taxa that lack oil bodies, and 3) isolating and structurally characterizing the compounds responsible for any activity observed. To this end, extracts from axenic cultures of Blasia pusilla L., Pallavicinia lyellii (Hook.) Carruth. and Radula obconica Sull. were tested for antimicrobial activity against Bacillus subtilis, Escherichia coli, and Aspergillus niger. Blasia retarded fungal sporulation, but displayed no inhibition of bacterial growth and Pallavicinia displayed only slight bacteriostatic activity against B. subtilis. Radula displayed the most pronounced antibacterial activity, especially against B. subtilis. These findings suggest that antimicrobial activity is more pronounced in taxa with oil bodies and confirm that bioactive compounds are still synthesized in axenic culture. The most active compounds in the fractions extracted from Radula are bibenzyls, compounds that are widespread in liverworts but of only sporadic occurrence in other plants.