Honors Theses and Capstones

Date of Award

Spring 2015

Project Type

Senior Honors Thesis

College or School



Molecular, Cellular and Biomedical Sciences

Program or Major

Biomedical Science: Medical Microbiology

Degree Name

Bachelor of Science

First Advisor

Louis S. Tisa


A novel Serratia sp (termed SCBI) forms an association with nematodes (South African Caenorhabditis briggsae) that were isolated by bait trapping in the greater wax moth, Galleria mellonella. This association represents a new microbe-nematode relationship and potentially a nascent entomopathogenic lifestyle. Inactivation of the hemolysin in Serratia sp. SCBI resulted in loss of hemolysis, but did not attenuate insecticidal activity. Unexpectedly, inactivation of the hemolysin gene in Serratia sp. SCBI resulted in significantly increased motility and a dramatic increase in mRNA levels of a nonribosomal peptide synthetase gene, swrA, which produces the surfactant serrawettin W2. A series of mutations in the 17 Kb swrA gene gave variable results in antibiotic activity, motility, virulence and hemolysin activities. The locations of three of the four mutations were confirmed by PCR analysis. The regulation of the expression of the swrA and hemolysin genes in swrA and hemolysin mutants was investigated by RT-qPCR using primer sets for different regions of these two genes. Furthermore, the cDNA of the 17 Kb transcript of swrA was generated by reverse transcription and was analyzed by PCR with the primers used to confirm the swrA mutants. Results indicate that the swrA transcript is expressed differently at various points in its sequence. Mutations appear to affect expression differently depending on the location, suggesting complex regulatory mechanisms and the presence of multiple promoters within the transcript.