@article{PieckHerlemannJuergensetal.2015,
  author    = {Pieck, Angelika and Herlemann, Daniel P. P. and Juergens, Klaus and Grossart, Hans-Peter},
  title     = {Particle-Associated Differ from Free-Living Bacteria in Surface Waters of the Baltic Sea},
  series = {Frontiers in microbiology},
  volume    = {6},
  journal   = {Frontiers in microbiology},
  publisher = {Frontiers Research Foundation},
  address   = {Lausanne},
  issn      = {1664-302X},
  doi       = {10.3389/fmicb.2015.01297},
  pages     = {13},
  year      = {2015},
  abstract  = {Many studies on bacterial community composition (BCC) do not distinguish between particle associated (PA) and free-living (FL) bacteria or neglect the PA fraction by pre-filtration removing most particles. Although temporal and spatial gradients in environmental variables are known to shape BCC, it remains unclear how and to what extent PA and FL bacterial diversity responds to such environmental changes. To elucidate the BCC of both bacterial fractions related to different environmental settings, we studied surface samples of three Baltic Sea stations (marine, mesohaline, and oligohaline) in two different seasons (summer and fall/winter). Amplicon sequencing of the 16S rRNA gene revealed significant differences in BCC of both bacterial fractions among stations and seasons, with a particularly high number of PA operational taxonomic units (OTUs at genus-level) at the marine station in both seasons. "Shannon and Simpson indices" showed a higher diversity of PA than FL bacteria at the marine station in both seasons and at the oligohaline station in fall/winter. In general, a high fraction of bacterial OTUs was found exclusively in the PA fraction (52\% of total OTUs). These findings indicate that PA bacteria significantly contribute to overall bacterial richness and that they differ from FL bacteria. Therefore, to gain a deeper understanding on diversity and dynamics of aquatic bacteria, PA and FL bacteria should be generally studied independently.},
  language  = {en}
}
@article{BizicIonescuIonescuGrossart2018,
  author    = {Bizic-Ionescu, Mina and Ionescu, Danny and Grossart, Hans-Peter},
  title     = {Organic Particles: Heterogeneous Hubs for Microbial Interactions in Aquatic Ecosystems},
  series = {Frontiers in microbiology},
  volume    = {9},
  journal   = {Frontiers in microbiology},
  publisher = {Frontiers Research Foundation},
  address   = {Lausanne},
  issn      = {1664-302X},
  doi       = {10.3389/fmicb.2018.02569},
  pages     = {15},
  year      = {2018},
  abstract  = {The dynamics and activities of microbes colonizing organic particles (hereafter particles) greatly determine the efficiency of the aquatic carbon pump. Current understanding is that particle composition, structure and surface properties, determined mostly by the forming organisms and organic matter, dictate initial microbial colonization and the subsequent rapid succession events taking place as organic matter lability and nutrient content change with microbial degradation. We applied a transcriptomic approach to assess the role of stochastic events on initial microbial colonization of particles. Furthermore, we asked whether gene expression corroborates rapid changes in carbon-quality. Commonly used size fractionated filtration averages thousands of particles of different sizes, sources, and ages. To overcome this drawback, we used replicate samples consisting each of 3-4 particles of identical source and age and further evaluated the consequences of averaging 10-1000s of particles. Using flow-through rolling tanks we conducted long-term experiments at near in situ conditions minimizing the biasing effects of closed incubation approaches often referred to as "the bottle-effect." In our open flow-through rolling tank system, however, active microbial communities were highly heterogeneous despite an identical particle source, suggesting random initial colonization. Contrasting previous reports using closed incubation systems, expression of carbon utilization genes didn't change after 1 week of incubation. Consequently, we suggest that in nature, changes in particle-associated community related to carbon availability are much slower (days to weeks) due to constant supply of labile, easily degradable organic matter. Initial, random particle colonization seems to be subsequently altered by multiple organismic interactions shaping microbial community interactions and functional dynamics. Comparative analysis of thousands particles pooled togethers as well as pooled samples suggests that mechanistic studies of microbial dynamics should be done on single particles. The observed microbial heterogeneity and inter-organismic interactions may have important implications for evolution and biogeochemistry in aquatic systems.},
  language  = {en}
}