Isolierung und Charakterisierung von Bakterien aus ...

II Abstract
Abstract
As microbial resistence against known antibiotics increases, the search for new
chemical structures becomes more important. Especially marine bacteria are of
particular research interest as natural product producer. To further asses the potential
marine bacteria from different sediments were isolated, cultivated and analyzed with
chemical and biomolecular methods. To bypass the limitations of existing methods for
natural product discovery the search for alternative strategies e.g. genome-based
strategies, is necessary. For example PCR-based screening with special primers is a fast
and efficient possibility to assess the potential of a species to produce natural products.
It can therefore be used to select isolates for further tests.
Over 50% of the investigated isolates (especially Actinobacteria and Firmicutes)
contained gene clusters for non-ribosomal peptidsynthetases (NRPS) or
polyketidsynthases (PKS) and/or show antimicrobial activity against some test
organisms. Of these isolates the representatives of Bacillus amyloliqufaciens were
chosen and their natural product production was compared to each other. The
investigation of equal taxa from different habitats is not common. Nine (out of ten)
Bacillus amyloliquefaciens isolates had secondary metabolite gene clusters and showed
differences in the production of natural products. A location-independent production of
different antimicrobial non-ribosomal lipopeptides (substance classes of surfactin, iturin
and fengycin) and twelve unknown substances could be shown. This demonstrates that
bacteria of the same taxon (16sRNA similarity ≥99,5 %) are a viable source for the
search of new substances.
Especially the taxa Bacillus and Streptomyces are known as good natural product
producer. Two isolates were chosen (gtP20b Bacillus sp. and C42 Streptomyces sp.) and
the metabolites and genomes were analyzed. The crude extract from isolate gtP20b
inhibited the test organisms Xanthomonas campestris and Candida glabrata and it could
detected gene clusters for NRPS with PCR. It produces non-ribosomal lipopeptides
(substance classes iturine, surfactine and fengycine) as well as six unknown substances
in culture. The genome sequencing revealed known NRPS gene clusters as well as
unknown gene clusters for PKS and NRPS/PKS hybrid. The detected lipopeptides of
isolate gtP20b were assigned to annotated NRPS gene clusters. The other putative gene
cluster of PKS and hybridsystems contain a potential for novel natural products. The
identification of these unknown gene cluster is still in progress.
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