Document Type

Honors Project

First Advisor

Dr. Stephen Baron

Degree Award Date

Spring 2012


Extracellular Complementation, PHB Depolymerase Synthesis, Bald Mutants, Streptomyces sp. 5A


Bacteriology | Biology | Cell Biology | Microbiology


The soil bacterium, Streptomyces sp. SA, secretes a PHB depolymerase that degrades polyhydroxybutyrate (PHB), a biodegradable plastic-like polymer. Bald (bld) mutants of this bacterium are incapable of forming aerial mycelium. In a previous study, two bld mutants were isolated and found to be deficient in PHB depolymerase synthesis as well. Extracellular complementation is a phenomenon in which certain bald mutants can restore aerial mycelium formation in other bld mutants when grown in close proximity (22). The goals of the present study were to determine the pattern of extracellular complementation and PHB depolymerase synthesis among these Streptomyces sp. 5A bld mutants. We observed four complementation classes among the bld mutants, which may be attributed to cross-feeding of extracellular signaling molecules produced in a hierarchical cascade, similar to that seen in Streptomyces coelicolor (23). When certain mutants were plated 3 days prior to their complementation partner, the latter initially inhibited aerial mycelium formation in the early strain, presumably due to a diffusible, extracellular inhibitor molecule. Aerial mycelium formation in the two PHB-depolymerase-deficient mutants could be restored by extracellular complementation, but not PHB depolymerase synthesis, suggesting that morphological differentiation and PHB depolymerase synthesis may not be linked. PHB depolymerase synthesis in the other mutants was stimulated by growth next to another mutant or wild type plated 3 days earlier, implying a diffusible inducer or autoinducer was secreted by the initial strain.