Date of Award

Winter 2011

Project Type


Program or Major


Degree Name

Master of Science

First Advisor

Louis S Tisa


Photorhabdus temperata is an invertebrate pathogen and nematode symbiont that is commonly used as a biological control agent in the management of commercial crop pests. The focus of this study was to investigate the poorly understood molecular elements involved in the expression of hemolysis and virulence in this bacterium. A 10,000 transposant library was screened using a blood agar plate assay to identify mutants altered in hemolytic activity. A total of 74 mutants displaying defective, delayed, or early hemolysis were identified and subsequently tested for altered virulence in the Greater Waxmoth, Galleria mellonella, using an in vitro mortality assay. Ten mutants delayed in pathogenesis were identified. Molecular analysis identified the sites of transposon insertion in 16 hemolysis mutants, eight of which also displayed delayed virulence. A critical finding of this study was the involvement of RNases in the regulation of hemolysis and pathogenesis.