The species comprising the fungal endophyte genus “Epichloë ”are symbionts of cool season grasses. About half the species in this genus are strictly vertically transmitted, and evolutionary theory suggests that these species must be mutualists. Nevertheless, Faeth and Sullivan (e.g., 2003) have argued that such vertically transmitted endophytes are ’usually parasitic,’ and Müller and Krauss (2005) have argued that such vertically transmitted endophytes fall along a mutualism-parasitism continuum. These papers (and others) have caused confusion in the field. We (...) used a systematic review to show that close to half of the published papers in this field incorrectly categorize the interaction. Here, we develop the argument that advantages and disadvantages are not the same things as mutualism and parasitism and that experimental evidence must be interpreted in the context of theory. We argue that, “contra ”Faeth and Sullivan, it is highly unlikely that such strictly vertically transmitted endophytes can be parasites, and that, “contra ”Müller and Krauss, it is inappropriate to apply the continuum concept to strictly vertically transmitted endophytes. We develop a mathematical model to support and illustrate our arguments. We use the model to clarify that parasitism “requires ”some degree of horizontal transmission, and that while it is appropriate to use the continuum concept when referring to the genus as a whole, or to species that possess horizontal transmission, we argue that it is inappropriate to use the concept when referring to species that are strictly vertically transmitted. (shrink)

Resistance to the drugs used in the treatment of many infectious diseases is increasing, while microbial infections are being found to be responsible for more life‐threatening diseases than previously thought. Despite a large investment in the invention and application of high‐throughput screening techniques involving miniaturization and automation, and a diverse array of strategies for designing and constructing various chemical libraries, relatively few new drugs have resulted. Natural products, however, have been a major source of drugs for centuries. Since some of (...) them are produced by organisms as a result of selection in favour of improved defense against competing deleterious microorganisms, in principle they would be less likely to incur resistance. Furthermore, the production of those defensive secondary metabolites is inducible because their original function is a response to environmental challenges. Moreover, symbioses, co‐habitation associations between two or more different species of organisms, are universal in nature, and the production of secondary metabolites by symbiotic microbes may be an important adaptation allowing microbes to affect their hosts. Therefore, co‐culture strategies, using combinations of plant cell–pathogenic microbes, plant cell–endophytes (or symbionts), and symbiont–pathogenic microbes, based on the principles of chemical defense and the known mechanisms of organism interactions, may be an efficient general approach in the search for new anti‐microbial drugs. BioEssays 26:808–813, 2004. © 2004 Wiley Periodicals, Inc. (shrink)