Dual sources of antimicrobial activity of Anemopsis californica : Plant and endophytic fungi (2014)

Anemopsis californica is a plant native to the southwestern United States and northern Mexico that has been used by many Native American tribes to alleviate pain and inflammation and to treat infection. Limited research has examined the chemical composition of A. californica responsible for its purported therapeutic properties. Goal 1 of this study was to identify pathogenic bacteria against which the plant extract was active, and isolate the compounds responsible for this activity. Goal 2 was to identify bioactive compounds from endophytic fungi isolated from the plant. The A. californica root extract was tested against a panel of bacteria and exhibited the most activity against several Mycobacterium spp. Bioassay-guided fractionation was conducted on a sample of A. californica roots was undertaken to isolate the bioactive compounds. These compounds were identified as the furofuran lignans sesamin (1) and asarinin (2), which were shown to have minimum inhibitory concentrations (MICs) ranging from 23 to 395 µM against five different species of environmental nontuberculous mycobacteria. These findings are significant given that these bacteria can cause skin, pulmonary, and lymphatic infections. With the use of liquid chromatography - mass spectrometry (LC-MS), it was determined that sesamin and asarinin were extracted at relatively high levels from A. californica roots (1.7-3.1g/kg and 1.1-1.7 g/kg, respectively), but lower levels from leaves (0.13 g/kg for both compounds). Our findings suggest that the majority of activity of crude A. californica root extracts against nontuberculous mycobacteria can be attributed to the presence of sesamin and asarinin. This is the first reported isolation of these compounds from a member of the Saururaceae family, and the first description of their activity against nontuberculous mycobacteria. Goal 2 of this project was to identify bioactive compounds from the fungal endophytes of A. californica (fungi living asymptomatically within the plant tissues). The fungal endophytes were extracted from the plant and cultured on a solid media. Twelve different fungi were identified. Crude extracts of these fungi were prepared and partitioned with liquid-liquid chromatography. Several antimicrobial compounds were isolated or identified from these fungi, including a new antimicrobial compound chaetocuprum A from the fungus Chaetomium cupreum. An additional nineteen compounds were also identified, of which six have been shown in literature or with our investigations to possess antimicrobial activity. In addition, a crude extract of the A. californica root was prepared from the same batch of roots from which fungi were isolated, to ascertain whether any of these antimicrobial compounds were present in the plant. None of the antimicrobial compounds isolated from the endophytes were detected in the extract, but a series of other fungal compounds were present. Finally, at least eighteen ions were detected as being present in both the botanical and fungal extracts. The structures of these "overlapping compounds" have not yet been solved, but their presence does suggest a potential role for fungi in the chemical composition of botanical extracts.