Increase in soil organic matter content enhances bacterial endophyte-dependent in vitro macrophage activity exhibited by Echinacea purpurea root material

Previous studies from our laboratory indicate that LPS and Braun type lipoproteins derived from endophytic bacteria within Echinacea are responsible for 97% of in vitro monocyte/macrophage activation by extracts of this botanical. Furthermore, we have found that changes in the levels of these two components are responsible for the variation (˜100-fold) observed in the activity of Echinacea material obtained from different commercial sources. In the current study we investigated whether agronomic factors known to influence endophyte community composition could be responsible for the wide variation in the activity that we observed in the commercially obtained plant material. Our results showed that cultivation of E. purpurea in soils containing increasing amounts of organic matter significantly enhanced the level of in vitro macrophage activation exhibited by extracts of the root material. Increasing soil organic matter content 2.5 times resulted in a 4-fold increase in macrophage activation potential exhibited by root material (p< 0.0001). Cultivation of plants in soil with different levels of moisture content did not significantly alter the level of macrophage activation exhibited by either E. purpurea root or aerial material. These results indicate that soil organic matter content is one agronomic factor that alters the amount and type of bacterial endophytes present and thereby contributes to the difference in macrophage activation potential exhibited by E. purpurea plant material.