What do we really know about bacterial secondary metabolite production?

Although humans have utilized the secondary metabolites produced by microorganisms for decades, our understanding of the role of these metabolites in the ecology of the producing organism remains minimal.  For soil genera such as Bacillus and Streptomyces, secondary metabolite production is thought to increase prior to the organism undergoing life cycle changes, including the processes of sporulation and programmed cell death.  However, recent work with members of the Streptomyces, Bacillus, and Vibrio genera grown in pure culture in liquid broth indicated that metabolite production was variable and not just associated with later life cycle changes.  These findings suggest that bacteria likely have numerous mechanisms to regulate production of secondary metabolism or have evolved mechanisms of communication to promote upregulation of metabolite expression in cultures during exponential growth.  Further investigations into the metabolite expression patterns of the isolates as they grow in liquid culture will help identify when and how secondary metabolites are expressed.  Additionally, the utilization of competition flasks with two growth chambers separated by a 0.1 micron filter will allow the examination of secondary metabolite expression patterns of isolates grown in pure culture but exposed to small molecules released by the ‘competing’ organism.  These studies may help to provide much needed information regarding the ecology of bacterial secondary metabolism.