title: Particle-Associated Differ from Free-Living Bacteria in Surface Waters of the Baltic Sea.
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 16 S 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.
authors.affiliation: Leibniz-Institute of Freshwater Ecology and Inland Fisheries Stechlin, Germany.
authors.forename: Angelika
authors.initials: A
authors.lastname: Rieck
authors.affiliation: Leibniz Institute for Baltic Sea Research Warnemünde Rostock, Germany.
authors.forename: Daniel P R
authors.initials: DP
authors.lastname: Herlemann
authors.affiliation: Leibniz Institute for Baltic Sea Research Warnemünde Rostock, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Jürgens
authors.affiliation: Leibniz-Institute of Freshwater Ecology and Inland Fisheries Stechlin, Germany ; Institute of Biochemistry and Biology, University of Potsdam Potsdam, Germany.
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Grossart
keywords: 454-pyrosequencing; Baltic Sea; microbial communities; microbial diversity; particle-associated and free-living bacteria; salinity gradient; seasons