hide
Free keywords:
-
Abstract:
The detailed investigation of microbial communities, e.g. of soil or hydrothermal vent
ecosystems, greatly improved our understanding of the diversity, habitat preferences and
functions of microorganisms and their impact on global element cycles. The aim of this
thesis was a detailed analysis of the diversity, abundance and distribution of
micoorganisms at marine methane seeps and the mechanisms that govern community
assembly at these sites. The seep ecosystems were investigated using geochemical
analyses, gene libraries, pyrosequencing, community fingerprinting and fluorescence in
situ hybridization. Cold seep ecosystems hosted distinct microbial communities that
differed from those of the surrounding seabed and were unique microbial habitat patches
in the deep sea. The communities also greatly differed between seeps, covered broad
ranges of richness and evenness and showed high degrees of endemism. However,
despite the differences all seeps were inhabited by certain organisms – the cold seep
microbiome - including key functional clades of anaerobic methane oxidizing archaea
(ANME) and sulfate-reducing bacteria. Additionally, aerobic methanotrophs and thiotrophs
were found at all seeps where oxygen was present. These key functional clades seemed
to be influenced by environmental parameters, such as temperature, fluid flux, sediment
depth and faunal activity. Bioirrigation by ampharetid tubeworms, for instance, created a
habitat for aerobic Methylococcales, whereas vesicomyid clams seemed to favor the
establishment of the clade ANME-2c. Thus, niche-based processes played an important
role for the community assembly at seep ecosystems. However, most of the seeps
seemed to be clearly dominated by a few, globally distributed operational taxonomic units
at 97% 16S rRNA gene identity (OTU0.03) of each key functional clade. Some of these
OTU0.03 were rare at some seep ecosystems and abundant at others. Moreover, some
findings suggested that rare organisms became abundant because the environmental
conditions at the seep changed supporting the importance of species sorting at seep
communities. Finally, the succession of microbial communities and the emergence of
ecosystem function at a cold seep were monitored showing that it may take years to
develop fully functioning communities that efficiently remove the potential greenhouse gas
methane. Overall this work may help to resolve the mysteries of microbial community
ecology at cold seep ecosystems.
