The number of reported Vibrio-related wound infections associated with recreational bathing in Northern Europe has increased within the last decades. In order to study the health risk from potentially pathogenic Vibrio spp. in the central Wadden Sea, the seasonal and spatial distribution of Vibrio vulnificus, Vibrio parahaemolyticus, Vibrio alginolyticus and Vibrio cholerae were investigated at ten recreational beaches in this area over a 2-year period. V. alginolyticus and V. parahaemolyticus were found to be omnipresent all year round in the study area, while V. vulnificus occurrence was restricted to summer months in the estuaries of the rivers Ems and Weser. Multiple linear regression models revealed that water temperature is the most important determinant of Vibrio spp. occurrence in the area. Differentiated regression models showed a species-specific response to water temperature and revealed a particularly strong effect of even minor temperature increases on the probability of detecting V. vulnificus in summer. In sediments, Vibrio spp. concentrations were up to three orders of magnitude higher than in water. Also, V. alginolyticus and V. parahaemolyticus were found to be less susceptible towards winter temperatures in the benthic environment than in the water, indicating an important role of sediments for Vibrio ecology. While only a very small percentage of tested V. parahaemolyticus proved to be potentially pathogenic, the presence of V. vulnificus during the summer months should be regarded with care.

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Guanosine 3'-diphosphate 5'-diphosphate (ppGpp) is rapidly degraded to guanosine 5'-diphosphate (ppG) and probably pyrophosphate by an enzyme present in the ribosomal fraction prepared from spoT' strains of Escherichia coli. The ppGpp-degrading enzyme was released from the ribosomes during dissociation at low ionic strength. Ribosomes are not essential for degradation of ppGpp, and decay of ppGpp is strictly dependent on manganese ions. The reaction is sensitive to inhibition by tetracycline, which can be reversed by MnC12, indicating that the inhibitory effect is due to the previously described chelating properties of the antibiotic. When the ppGpp-degrading enzyme was complemented with adenosine 5'-triphosphate (pppA) and a nucleoside diphosphate kinase, decay of ppGpp was accelerated yielding pppG and ppG as major products. In the absence of pppA we have been unable to detect the ppGpp-degrading enzyme in various SPOT-mutant strains indicating that this enzyme is the spoT gene product.

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Degradation of guanosine tetraphosphate (ppGpp) involves an enzyme associated with the ribosomal fraction from spoT'strains of Escheric4ia coli. Double Auxotrophic strains of Escherichia coli are known to accumulate rapidly the unusual nucleotides guanosine 5'-diphosphate 3'-diphosphate (ppGpp) and guanosine 5'-triphosphate 3'-diphosphate (pppGpp) when deprived of an essential amino acid (for reviews, see refs. 1 and 2). It has been proposed that (p)ppGpp functions as a pluripotent regulator molecule that controls a number of biosynthetic and catabolic pathways; it restricts synthesis of stable RNA (3), of purine nucleotides (4), of glycolytic esters (5), and of phospholipids (6).In order to elucidate the function of (p)ppGpp as a major regulator molecule in bacterial cells, it is essential to understand the precise mechanism of its synthesis and degradation as well. The mode of synthesis of (p)ppGpp has been discovered by Haseltine et al. (7) who showed that these compounds are synthesized on ribosomes by an enzyme named "stringent factor." Despite attempts by a number of groups, the mechanism of ppGpp breakdown has remained unresolved until recently (8, 9). Although, in vivo, ppGpp is rapidly degraded when E. coli cells are resupplemented with the lacking amino acid (10), attempts to demonstrate degradation in vitro have failed (11)(12)(13)(14)(15). Genetic studies have shown that in vivo breakdown of ppGpp is associated with the spoT+ allele; in spoTmutants, ppGpp breakdown is significantly slower than in wild-type strains (16,17). This may indicate that spoT-mutants either have a similar but less active degradation device or utilize an alternative pathway. The enzyme involved and the mechanism of ppGpp breakdown are the subject of this communication. MATERIALS AND METHODSThe ppGpp degrading enzyme was prepared from the stringent E. coli strains CGSC 2834/a (relA +) and CP78 (relA +, CCA+, his-, leu-, arg-, thr-, B1-) or from the relaxed strain CP79 (relA-, CCA-, his-, leu-, arg-, thr-, BR -); CP78 and CP79 were kindly provided by M. Deutscher (Farmington, CT); K10 (spoT-, relA-, tonA22) were from A. Bock (Regensburg, Germany). [8-3H]GTP (New England Nuclear, Boston, MA) was used for preparation of pp[3H]Gpp (specific activity, 2

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Salmonella contamination of North Sea water was detected for the first time in 1988 in Germany during routine examinations of bathing areas. Since then, subsequent isolations along the coast have been reported regularly. To define the source of contamination, strains isolated from seawater and rivers were studied by molecular marker methods. Their properties were compared with those of strains originating from possible sources of contamination such as humans, cattle, and sewage treatment plant water. Plasmid profile analysis of whole bacterial populations and the determination of antibiotic resistance patterns demonstrated, that contamination through the surrounding cattle industry could be excluded. Cattle isolates belonged to a widespread clone of phage type 204c which was multiresistant and exhibited an unique plasmid pattern which was never found in sea water isolates. Outer membrane protein and lipopolysaccharide analysis failed to demonstrate differences among the Salmonella populations and proved in this case insufficient for molecular marker discrimination.

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