Heindl, Herwig (2011) Antimicrobially active microorganisms associated with marine bryozoans. (PhD/ Doctoral thesis), Christian-Albrechts-Universität, Kiel, Germany, 108 pp.

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Abstract

Bryozoans are sessile colonial animals that can be found in various aquatic and mainly in marine environments. Due to their sessile nature, bryozoans compete for surfaces they can colonize but, on the other hand, are confronted with microbial colonizers on their surfaces. Interactions of the bryozoan with its associates, as well as within the microbial community, are mediated chemically. Biofilm formation and composition is mainly influenced by the use of chemical compounds. Studies on the bryozoan-associated microbial diversity are scarce, and surveys on the antimicrobial potential of these associated bacteria are missing. The present study focused on isolating bryozoan-associated bacteria, assessing their antimicrobial properties and classifying them phylogenetically. Various bryozoan specimens were collected in the Baltic (10 specimens) and the Mediterranean Sea (11 specimens). Bacteria were isolated using a variety of nutrient media and tested for their antimicrobial abilities against Gram-positive and Gram-negative indicator strains, as well as against the yeast Candida glabrata. 30% of all isolates displayed activity and were phylogenetically classified on the basis of 16S rDNA gene sequences. Whereas all isolates were active against Gram-positive indicators, four isolates exhibited additional anti-Escherichia coli activity, the phylogenetic analysis revealed affiliation to Gram-negative phyla (Flavobacteria, Alpha- and Gammaproteobacteria). One isolate belonged to the Gram-positive Actinobacteria. Both species- and strain-specific activity patterns were revealed. Furthermore, site-specific distribution patterns of associated bacteria were found. Of these antibiotically active isolates, the strain B390 was described as type strain of the novel species Tenacibaculum adriaticum. Also, specimens of the bryozoan Membranipora membranacea were sampled in the Baltic Sea for the first more detailed analysis on antimicrobially active isolates. Low-nutrient media featuring “artificial” or “natural” ingredients were used for isolation of bacteria. Additionally, the antibiotic test panel was extended to six different production media. The impact of these media on the phylogenetic diversity, as well as on activity patterns was determined. Although bacteria were affiliated with same phyla (Alpha- and Gammaproteobacteria, Actinobacteria, additionally Bacilli), the isolates of this sampling were more diverse as far as genus or phylotype affiliation was concerned. Especially within the Alphaproteobacteria, several probably novel bacterial species were found. Furthermore, the use of six different media for activity testing resulted in a more than twofold higher hit rate of active isolates in comparison to only one single medium.

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