Vibrio spp. in the German Bight

  • Pathogenic Vibrio strains represent an increasing health issue in European waters, but profound investigations on Vibrio spp. are lacking, especially in northern European waters. This thesis represents a pilot study for the German Bight, investigating the Vibrio community extensively, with special emphasis on V. parahaemolyticus. Insights into abundance, community composition and response to environmental parameters of Vibrio spp. at Helgoland Roads (North Sea, Germany) were obtained. Using a cultivation-independent approach, Vibrio numbers up to 3.37 x 104 cells x mL 1 were detected at Helgoland Roads. Targeting solely potentially pathogenic Vibrio spp., numbers up to 4.3 x 103 N x L-1 (water, plankton) and 240 MPN x g 1 (shellfish) were quantified using a selective cultivation approach. In the course of this thesis, a broad range of microbiological and molecular biological methods have been evaluated regarding the usefulness for the investigation of Vibrio spp. and the potentially pathogenic species V. parahaemolyticus. A reliable, cost- and labor-effective approach was defined including (i) the sequencing of the rpoB gene (encoding the RNA polymerase β-subunit) to differentiate even closely related Vibrio species, (ii) the use of the toxR gene as specific marker for V. parahaemolyticus, (iii) the screening for the virulence-associated genes tdh and trh, and (iv) the performance of genomic fingerprinting using ERIC-PCR to identify the intraspecies variability of V. parahaemolyticus and its close relative V. alginolyticus at Helgoland Roads. Applying this polyphasic approach, we gathered insights into the Vibrio community at Helgoland Roads. Vibrio strains were isolated from seawater, plankton and shellfish and the species V. parahaemolyticus appeared to be the second most abundant species at Helgoland Roads, behind its close relative V. alginolyticus. None of the V. parahaemolyticus strains carried the virulence-associated genes tdh or trh, but several strains were proven positive for hemolytic activity. Based on genomic fingerprinting of V parahaemolyticus and V. alginolyticus strains, three distinct groups became evident. One group represented V. parahaemolyticus, the second one V. alginolyticus. The third group was located in between the two species, displaying the high genomic plasticity and intraspecific variability of Vibrio spp.. To be able to estimate the distribution and dynamics of Vibrio spp. in response to environmental conditions, we assessed the effects of environmental parameters on the Vibrio community. High temperature in combination with events of low salinity and high abundance of phytoplankton led to increased Vibrio numbers at Helgoland Roads. The influence of the parameters, however, varied between the seasons. The population of the potentially pathogenic species V. parahaemolyticus at Helgoland Roads appeared to be structured by a complex combination of parameters, including temperature, NO3 , salinity, dinoflagellates, SiO2, secchi depth and NO2. Changing environmental conditions might not only lead to increasing numbers of Vibrio spp. in the German Bight, but also to a community shift towards potentially pathogenic species such as V. parahaemolyticus. Being the first profound study on Vibrio spp. in the German Bight, this thesis represents an invaluable first step towards the understanding of this important microbial group, harboring the potential pathogen V. parahaemolyticus, in northern European waters.

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Publishing Institution:IRC-Library, Information Resource Center der Jacobs University Bremen
Granting Institution:Jacobs Univ.
Author:Sonja Oberbeckmann
Referee:Karen Wiltshire, Gunnar Gerdts, Antje Wichels, Matthias Ullrich
Advisor:Karen Wiltshire
Persistent Identifier (URN):urn:nbn:de:101:1-2013052812405
Document Type:PhD Thesis
Date of Successful Oral Defense:2011/03/07
Date of First Publication:2011/04/15
PhD Degree:Marine Microbiology
School:SES School of Engineering and Science
Library of Congress Classification:Q Science / QR Microbiology / QR100-131 Microbial ecology / QR106 Seawater. Marine microbiology
Call No:Thesis 2011/10

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