TY - JOUR A1 - Bizic-Ionescu, Mina A1 - Zeder, Michael A1 - Ionescu, Danny A1 - Orlic, Sandi A1 - Fuchs, Bernhard M. A1 - Grossart, Hans-Peter A1 - Amann, Rudolf T1 - Comparison of bacterial communities on limnic versus coastal marine particles reveals profound differences in colonization JF - Environmental microbiology N2 - Marine and limnic particles are hotspots of organic matter mineralization significantly affecting biogeochemical element cycling. Fluorescence in-situ hybridization and pyrosequencing of 16S rRNA genes were combined to investigate bacterial diversity and community composition on limnic and coastal marine particles >5 and >10m respectively. Limnic particles were more abundant (average: 1x10(7)l(-1)), smaller in size (average areas: 471 versus 2050m(2)) and more densely colonized (average densities: 7.3 versus 3.6 cells 100m(-2)) than marine ones. Limnic particle-associated (PA) bacteria harboured Alphaproteobacteria and Betaproteobacteria, and unlike previously suggested sizeable populations of Gammaproteobacteria, Actinobacteria and Bacteroidetes. Marine particles were colonized by Planctomycetes and Betaproteobacteria additionally to Alphaproteobacteria, Bacteroidetes and Gammaproteobacteria. Large differences in individual particle colonization could be detected. High-throughput sequencing revealed a significant overlap of PA and free-living (FL) bacteria highlighting an underestimated connectivity between both fractions. PA bacteria were in 14/21 cases more diverse than FL bacteria, reflecting a high heterogeneity in the particle microenvironment. We propose that a ratio of Chao 1 indices of PA/FL<1 indicates the presence of rather homogeneously colonized particles. The identification of different bacterial families enriched on either limnic or marine particles demonstrates that, despite the seemingly similar ecological niches, PA communities of both environments differ substantially. Y1 - 2015 U6 - https://doi.org/10.1111/1462-2920.12466 SN - 1462-2912 SN - 1462-2920 VL - 17 IS - 10 SP - 3500 EP - 3514 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Bizic-Ionescu, Mina A1 - Amann, Rudolf A1 - Grossart, Hans-Peter T1 - Massive regime shifts and high activity of heterotrophic bacteria in an ice-covered lake JF - PLoS one N2 - In winter 2009/10, a sudden under-ice bloom of heterotrophic bacteria occurred in the seasonally ice-covered, temperate, deep, oligotrophic Lake Stechlin (Germany). Extraordinarily high bacterial abundance and biomass were fueled by the breakdown of a massive bloom of Aphanizomenon flos-aquae after ice formation. A reduction in light resulting from snow coverage exerted a pronounced physiological stress on the cyanobacteria. Consequently, these were rapidly colonized, leading to a sudden proliferation of attached and subsequently of free-living heterotrophic bacteria. Total bacterial protein production reached 201 mg C L-1 d(-1), ca. five times higher than spring-peak values that year. Fluorescence in situ hybridization and denaturing gradient gel electrophoresis at high temporal resolution showed pronounced changes in bacterial community structure coinciding with changes in the physiology of the cyanobacteria. Pyrosequencing of 16S rRNA genes revealed that during breakdown of the cyanobacterial population, the diversity of attached and free-living bacterial communities were reduced to a few dominant families. Some of these were not detectable during the early stages of the cyanobacterial bloom indicating that only specific, well adapted bacterial communities can colonize senescent cyanobacteria. Our study suggests that in winter, unlike commonly postulated, carbon rather than temperature is the limiting factor for bacterial growth. Frequent phytoplankton blooms in ice-covered systems highlight the need for year-round studies of aquatic ecosystems including the winter season to correctly understand element and energy cycling through aquatic food webs, particularly the microbial loop. On a global scale, such knowledge is required to determine climate change induced alterations in carbon budgets in polar and temperate aquatic systems. Y1 - 2014 U6 - https://doi.org/10.1371/journal.pone.0113611 SN - 1932-6203 VL - 9 IS - 11 PB - PLoS CY - San Fransisco ER -