ABSTRACT The transcriptional organization and heat inducibility of the major heat shock genes hrcA , dnaK , dnaJ , groEL , and htpG were analyzed on the transcriptional level in Helicobacter pylori strain 69A. The strongly heat-induced dnaK operon was found to be tricistronic, consisting of the genes hrcA , grpE , and dnaK . The dnaJ gene specified one monocistronic mRNA which was also heat inducible. The genes groES and groEL were transcribed as one strongly heat-inducible bicistronic mRNA which exhibited exactly the same induction kinetic as the dnaK operon. Surprisingly, transcription of the monocistronic htpG gene was switched off after heat shock. The data presented are discussed with regard to the different mechanisms regulating expression of heat shock genes in H. pylori

High ammonia levels in mammalian tissues, especially blood (as well as in urine), are toxic, causing severe metabolic disorders. The underlying pathogenic principles are for the most part poorly understood. In this review we discuss 1) possible mechanisms of ammonia toxicity, 2) general mechanisms of bacterial ammonia production and 3) Klebsiella virulence. Special reference is made to possible effects of nitrogen fixation, ureolysis, proteolysis and amino acid ammonification.

Physiological techniques were used to separate two related Dreissena species initially established by electrophoretic and morphological characteristics (May and Marsden. 1992. Can. J. Fish. Aquat. Sci. 49: 1501-1506). Samples of zebra mussels (Dreissena polymorpha) and "quagga" mussels (provisionally either Dreissena polymorpha andrusovi or Dreissena rostriformis bugensis) of the same size growing side by side were collected in Lake Erie, thereby ensuring that they had identical thermal histories. Upper lethal temperatures of zebra mussels were significantly higher than those of quagga mussels. The critical thermal maxima of zebra mussels acclimatized at 20-degrees-C were half a degree higher than those of quagga mussels. The average survival times of zebra mussels held at a constant lethal temperature were also significantly longer. These results indicate that in addition to differences in allozyme loci and shell morphology, these two dreissenids may be distinguished by important physiological differences in their thermal resistance; moreover, there may be important ecological differences associated with the different species of dreissenids in North America.