Struktur und räumliche Verteilung mikrobieller Gemeinschaften im Verdauungstrakt ausgewählter Boden-Invertebraten
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Abstract
Soil macroinvertebrates play an important role in
the transformation of soil organic matter, which is responsible
for many key soil functions. During gut passage of ingested
soil organic matter, intestinal microorganisms participate in
the transformation processes, which are also of great
importance for the nutrition of their hosts. However, little is
known about the structure of microbial communities in the
intestinal tract of most soil macroinvertebrates and their
spatial distribution within different gut sections. In fact,
particularly the topology of microbial communities is regarded
as a prerequisite for a deeper understanding of the
functionality of invertebrate intestinal tracts, which are
characterized by pronounced axial and radial gradients of
important physicochemical parameters.
Therefore, in the course
of this thesis structure and topology of microbial communities
in the intestinal tract of the larva of two scarabaeid beetles
(Pachnoda ephippiata and Melolontha melolontha) and in the
midgut of the earthworm Lumbricus terrestris were analyzed
applying techniques of molecular microbial ecology. Moreover, a
novel PCR-artifact, so called pseudo-T-RFs, was detected during
this thesis, markedly affecting T-RFLP analysis of microbial
communities. Protocols allowing the identification and
prevention of pseudo-T-RFs formation were developed and
applied. In a T-RFLP-based study with earthworms it could be
shown, that the intestinal microbiota of these animals is
largely soil-derived, i.e. that they lack a gut-specific flora
typical for many other soil invertebrates. It could be shown
that the ingested microbial community undergoes significant
changes during gut passage and that the differences in
microbial community composition between food soil, gut and
casts strongly depend on the diet of the earthworms.
The
studies conducted with scarabaeid beetle larvae were the first
comprehensive molecular studies about the gut microbiota of
beetle larvae and among the first studies about the gut
microbiota of other soil arthropods than termites. It could be
shown that the pronounced differences in physicochemical
parameters existing between the two major gut sections (midgut
and hindgut) of scarabaeid beetle larvae are paralleled by
marked differences in the colonization with microorganisms. In
contrast to the investigated earthworms, the gut microbiota of
the scarabaeid beetle larvae could be regarded as a special gut
flora, because its composition was considerably different to
the microbial community of the ingested food. In both larval
species the midgut section was less densely colonized than the
hindgut, which possibly functions as a fermentation chamber.
Methanogenesis was always restricted to the hindgut section; in
the larva of M. melolontha, Methanobrevibacter-species were
identified to account for methane production, in P. ephippiata
larvae additionally Methanomicrococcus-species occurred.
However, in comparison to Bacteria, diversity and relative
abundance of Archaea was low. Phylogenetic analysis of the
intestinal bacterial communities revealed a high diversity,
obviously comprising many so far uncultivated species. The
majority of sequences was affiliated with Actinobacteria,
Bacillales, Bacteroidetes, Clostridiales, Lactobacillales, and
Proteobacteria; many clones were grouping with clones and
isolates from other intestinal systems, which underlined the
gut specificity of the intestinal microbiota of the scarabaeid
beetle larvae. The affiliation of many clones with hydrolytic,
cellulolytic and fermenting isolates corroborated the
intestinal fatty acid spectra (dominated by acetate and
lactate) and suggests the existence of an anaerobic food chain,
at least for the hindgut sections. It is not clear if this also
holds true for the midgut, since in case of the Melolontha
larvae no stable bacterial community could be proven for this
gut section.
The Melolontha larvae investigated during this
thesis were the first arthropods with which a comprehensive
analysis of the microbial community structure of different
subcompartmental fractions of major gut sections was performed.
The gut wall and lumen fractions of the Melolontha hindgut were
found to be differentially colonized by microorganisms, which
may reflect adaptations to morphological (occurrence of chitin
trees at the hindgut wall) and/or physicochemical (penetration
of oxygen into the hindgut periphery) features of the
investigated subcompartments. The most noticeable difference
between the microbial communities of hindgut wall and lumen was
a high abundance (10 - 15% of all bacteria) of
Desulfovibrio-related bacteria at the hindgut wall, proven with
both PCR-dependent and ?independent methods. Regarding
its clearness, this finding is so far unique for
arthropods.
Review
Metadata
Contributors
Supervisor:
Dates
Created: 2003Issued: 2004-01-14Updated: 2011-08-10
Faculty
Fachbereich Biologie
Publisher
Philipps-Universität Marburg
Language
ger
Data types
DoctoralThesis
Keywords
16S rRNA-GenBacteriabeetle larvae , digestiongut , earthwormArchaea , Scarabaeidaemicrobial ecologyMikrobielle Ökologie
DFG-subjects
RegenwurmDarm , ProkaryontenMaikäferVerdauungRosenkäferTopologieÖkologie
DDC-Numbers
570
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Egert, Markus (128691964): Struktur und räumliche Verteilung mikrobieller Gemeinschaften im Verdauungstrakt ausgewählter Boden-Invertebraten. : Philipps-Universität Marburg 2004-01-14. DOI: https://doi.org/10.17192/z2004.0064.
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This item has been published with the following license: In Copyright