Degree Type


Date of Award


Degree Name

Doctor of Philosophy




Bacteriocins are proteins released by bacteria that prevent the growth of other microorganisms. A bacteriocin produced by Propionibacterium thoenii P127 is a small, heat-labile protein that we have designated propionicin PLG-1. Propionicin PLG-1 is inactivated by heat (30 min at 85°C) and exhibits a bactericidal mode of action against sensitive indicator organisms. Propionicin PLG-1 is active against some but not all of the classical propionibacteria, some gram-positive organisms, some gram-negative organisms, and some yeasts and molds. Propionicin PLG-1 is inactivated by [alpha]-chymotrypsin, protease, papain, pepsin, and trypsin, but not by lipase and phospholipase C or catalase;Accumulation of propionicin PLG-1 in the culture supernatant during stationary growth phase is characteristic of a secondary metabolite. Optimal production occurs at pH 7.0. Propionicin PLG-1 (MW 10,000) was purified by applying a protein fraction precipitated with ammonium sulfate to a carboxymethyl sepharose column. An active fraction eluted from the column was evaluated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), and it was found to contain several contaminating proteins. When this protein fraction containing propionicin activity was isoelectrically focused, a single active fraction was obtained. A single band was detected in this fraction by SDS-PAGE;The producing strain harbors a single plasmid (pLG1) with approximate molecular weight 250 kb. Mutants deficient in propionicin PLG-1 activity were isolated after exposing strain P127 to N-methyl-N[superscript]'-nitro-N-nitrosoguanidine and acriflavin. Some of the isolates lost immunity to the bacteriocin, while others retained immunity. Some of these mutants contained plasmid pLG1 while others lost the plasmid. The presence of the plasmid in the strain could not be correlated with carbohydrate fermentation, pigment production, or growth rate. These data suggest that both propionicin PLG-1 and immunity to the bacteriocin are encoded on the chromosome. Plasmid pLG1 remains cryptic.



Digital Repository @ Iowa State University,

Copyright Owner

Wanda Jean Lyon



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132 pages

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Microbiology Commons