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Abstract
The purpose of the present study was to analyze the composition of marine bacterial
communities around the world, and to investigate bacterial isolates regarding the production of
antibiotics. This included molecular analyses of marine bacterioplankton, as well as culture-based
studies of marine bacterial isolates with antagonistic activity. The work was based on samples
collected during the Galathea 3 and LOMROG-II marine research expeditions that have explored
many different oceanic regions worldwide.
A molecular survey of marine bacterioplankton at 24 worldwide stations investigated the
abundance of major bacterial groups, potential biogeographical patterns, and their relation to
environmental parameters. The original aim was to determine whether the composition of the total
microbiota correlates with the occurrence of culturable bioactive bacteria. No such correlation was
found. Quantitative community analyses showed latitudinal patterns in bacterial distribution,
revealing significantly different relative abundances of Bacteroidetes, unclassified Bacteria and
Vibrio between warmer and colder oceans. Absolute cell numbers of most bacterial groups were
positively correlated with nutrient concentrations in warmer oceans, and negatively with oxygen
saturation in colder oceans. The finding of differing communities in warmer and colder oceans
underlined the presence of biogeographical patterns among marine bacteria and the influence of
environmental parameters on bacterial distribution.
Studies of antagonistic isolates focused on six bioactive Vibrionaceae isolated during
Galathea 3. The six strains were identified as Vibrio coralliilyticus (two strains), V. neptunius (two
strains), V. nigripulchritudo (one strain), and Photobacterium halotolerans (one strain) by
sequencing of housekeeping genes. Chemical metabolite profiling underlined genetic relationships
by showing highly similar production of secondary metabolites for each species. Two known
antibiotics were purified; andrimid from V. coralliilyticus and holomycin from P. halotolerans. In
addition, two novel cyclic peptides from P. halotolerans and a novel siderophore-like compound
from V. nigripulchritudo were isolated. All three compounds interfere with quorum sensing in S.
aureus.
During LOMROG-II further seventeen strains with antagonistic activity were isolated,
affiliating with the Actinobacteria (8 strains), Pseudoalteromonas (4 strains), the Vibrionaceae (3
strains), and Psychrobacter (2 strains). Seven of the eight bioactive Actinobacteria, being isolated
from different sources throughout the Arctic Ocean, were related to Arthrobacter davidanieli. Its broad antibiotic spectrum was likely based on production of the known arthrobacilin antibiotics.
The eighth actinomycete, tentatively identified as Brevibacterium sp., produces a potentially novel
antimicrobial compound.
Most studies of antagonistic marine bacteria have been conducted with the aim of isolating
novel antimicrobials with potential clinical applications. However, little is known about production
and role of these compounds in the natural environment. This thesis took one step in this direction
and demonstrated that V. coralliilyticus S2052 produced its antibiotic andrimid when grown with
chitin as the sole carbon source. Whilst the strain produced an array of secondary metabolites in
laboratory media, it focused on andrimid production with chitin. This indicates that the antibiotic is
likely produced in the natural habitat and may serve an ecophysiological function. The finding that
two related strains from public culture collections do not produce andrimid and have different
biosynthetic temperature optima suggested that V. coralliilyticus may comprise different subspecies
with different niches.
In summary, the present study shows biogeographical patterns of marine bacterioplankton
on a global scale. In addition, the thesis work has demonstrated that marine Vibrionaceae and polar
Actinobacteria are a resource of antibacterial compounds and may have potential for future natural
product discovery.
Original language | English |
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Place of Publication | Kgs. Lyngby, Denmark |
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Publisher | Technical University of Denmark |
Number of pages | 168 |
ISBN (Print) | 978-87-92158-97-0 |
Publication status | Published - Apr 2011 |
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Dive into the research topics of 'Global patterns of marine bacterioplankton diversity and characterisation of bioactive Vibrionaceae isolates'. Together they form a unique fingerprint.Projects
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Global patterns of marine bacterioplankton diversity and characterisation of bioactive Vibrionaceae isolates
Wietz, M., Gram, L., Molin, S., Burgess, J. G. & Simon, M.
Technical University of Denmark
01/02/2008 → 14/04/2011
Project: PhD