Date of Award

Spring 1983

Project Type


Program or Major


Degree Name

Doctor of Philosophy


The recycling fermentor has been shown to be a good tool for studying microorganisms at very slow growth rates. Previous studies have determined that there are three distinct phases of growth based on biomass. Phase 3 has been shown to be initiated by the induction of the stringent response and to be regulated by the levels of guanosine 5'-diphosphate 3'-diphosphate (ppGpp) within the cell. By comparing the growth patterns of three enterotoxigenic Escherichia coli strains to that of E. coli strains of known rel genotypes, the Rel phenotypes of the enterotoxigenic strains were determined.

Both enterotoxin production and secretion in E. coli H10407 grown at pH 8.5 were shown to be positively controlled by ppGpp during phases 2 and 3, while tryptophanase and (beta)-galactosidase were more negatively affected by ppGpp. An enhancing effect by glucose was found on the production of enterotoxin and (beta)-galactosidase. The nicking process of enterotoxin activation appears to be regulated by ppGpp and may be an energy-dependent process.

A comparison of the growth patterns of enterotoxigenic E. coli 711 P307 and 711 P307 crp, a mutant lacking the cAMP receptor protein (CRP), in the recycling fermentor showed no change in the length of phase 2. However, the growth yield of 711 P307 crp was lower, particularly during a glucose upshift, than that of 711 P307. Tryptophanase and (beta)-galactosidase were produced by 711 P307, but were not produced by 711 P307 crp. A ten-fold higher concentration of enterotoxin was seen in 711 P307 than in the crp mutant. Both enterotoxin production and secretion and tryptophanase production were stimulated by the presence of ppGpp in 711 P307. Enterotoxin in 711 P307 crp showed only slight stimulation by ppGpp. The nicking process in both strains appears to be under negative control by ppGpp and may be an energy-dependent process. The patterns of enterotoxin production and secretion are similar in H10407 and 711 P307, but not in 711 P307 crp. This suggests that enterotoxin production as well as tryptophanase and (beta)-galactosidase production are regulated by both ppGpp and cAMP.