Date of Award

Fall 2001

Document Type


Degree Name

Master of Science (MS)


Biological Sciences



Committee Director

Wayne L. Hynes

Committee Member

Robert E. Ratzlaff

Committee Member

Christopher Osgood

Call Number for Print

Special Collections LD4331.B46 .H34 2001


Streptococcus iniae is a gram-positive organism responsible for causing disease in both freshwater as well as saltwater fish. Every year fisheries lose fish by the tons due to diseases caused by this organism. In 1991, the first reported human case of disease associated with this organism was described. Since this initial case, there have been numerous other reported cases of S. iniae infections. This organism is a catalase negative, facultatively anaerobic organism that produces a capsule and when plated onto blood agar demonstrates β-hemolytic activity.

In this study, the relationship between the hemolysin produced by S. iniae and the lactate oxidase gene (lctO) encoded by this organism was examined. Lactate oxidase is responsible for catalyzing the oxidation of L-lactate with molecular oxygen. Based on cloning studies, it had been suggested that this gene has a role in the hemolysis caused by S. iniae (unpublished observations). Two methods were chosen to determine whether the gene encoding lactate oxidase is associated with this hemolytic activity. The first method was a direct approach involving the inactivation of the lctO gene through homologous recombination with an inactive form of the gene. The second method entailed a more indirect approach using transposon mutagenesis. Electransformation experiments resulted in a protocol to transform S. iniae cells (not reported at start of these studies), however, the functional relationship between the hemolysin of S. iniae and the lctO gene could not be determined.

Also included in this study was a preliminary characterization of the hemolysin expressed by S. iniae. This hemolysin is found extracellularly and begins to be produced at the beginning of the exponential phase of growth (strain A TCC 291 78). It is believed to be a protein of greater than 12000 MW and demonstrates reduced activity when subjected to treatment with proteinase K suggestive of a protein moiety. The hemolytic activity also showed stability at elevated temperatures and incubation with cholesterol resulted in reduced hemolytic activity.


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