@article{WurzbacherSalkaGrossart2012,
  author    = {Wurzbacher, Christian and Salka, Ivette and Grossart, Hans-Peter},
  title     = {Environmental actinorhodopsin expression revealed by a new in situ filtration and fixation sampler},
  series = {Environmental microbiology reports},
  volume    = {4},
  journal   = {Environmental microbiology reports},
  number    = {5},
  publisher = {Wiley-Blackwell},
  address   = {Hoboken},
  issn      = {1758-2229},
  doi       = {10.1111/j.1758-2229.2012.00350.x},
  pages     = {491 -- 497},
  year      = {2012},
  abstract  = {Freshwater Actinobacteria are an important and dominant group of bacterioplankton in most temperate freshwater systems. Recently, metagenomic studies discovered rhodopsin-like protein-coding sequences present in Actinobacteria which could be a decisive hint for their success in freshwater ecosystems. We analysed the diversity of actinorhodopsin (ActR) in Lake Stechlin (northern Germany) and assessed the actR expression profile during a diurnal cycle. We obtained 85 positive actR clones which could be subsequently grouped to 17 operational taxonomic units assuming a 90\% sequence similarity. The phylogenetic analysis points to a close relationship of all obtained sequences to the acI lineage of Actinobacteria, forming six independent clusters. For the first time, we followed in situ transcription of actR in Lake Stechlin revealing a rather constitutive circadian gene expression. For analysing in situ expression patterns of functional genes in aquatic ecosystems, such as actR, we invented a new in situ filtration and fixation sampler (IFFS). The IFFS enables the representative investigation of microbial transcriptomes in any aquatic ecosystem at all water depths. The IFFS sampler is simple and inexpensive, and we provide all engineering plans for an easy rebuild. Consequently, our IFFS is suitable to reliably study expression of any known functional gene of any aquatic microorganism.},
  language  = {en}
}
@article{EigemannHiltSalkaetal.2013,
  author    = {Eigemann, Falk and Hilt, Sabine and Salka, Ivette and Grossart, Hans-Peter},
  title     = {Bacterial community composition associated with freshwater algae species specificity vs. dependency on environmental conditions and source community},
  series = {FEMS microbiology ecology},
  volume    = {83},
  journal   = {FEMS microbiology ecology},
  number    = {3},
  publisher = {Wiley-Blackwell},
  address   = {Hoboken},
  issn      = {0168-6496},
  doi       = {10.1111/1574-6941.12022},
  pages     = {650 -- 663},
  year      = {2013},
  abstract  = {We studied bacterial associations with the green alga Desmodesmus armatus and the diatom Stephanodiscus minutulus under changing environmental conditions and bacterial source communities, to evaluate whether bacteriaalgae associations are species-specific or more generalized and determined by external factors. Axenic and xenic algae were incubated in situ with and without allelopathically active macrophytes, and in the laboratory with sterile and nonsterile lake water and an allelochemical, tannic acid (TA). Bacterial community composition (BCC) of algae-associated bacteria was analyzed by denaturing gradient gel electrophoresis (DGGE), nonmetric multidimensional scaling, cluster analyses, and sequencing of DGGE bands. BCC of xenic algal cultures of both species were not significantly affected by changes in their environment or bacterial source community, except in the case of TA additions. Species-specific interactions therefore appear to overrule the effects of environmental conditions and source communities. The BCC of xenic and axenic D.armatus cultures subjected to in situ bacterial colonization, however, had lower similarities (ca.55\%), indicating that bacterial precolonization is a strong factor for bacteriaalgae associations irrespective of environmental conditions and source community. Our findings emphasize the ecological importance of species-specific bacteriaalgae associations with important repercussions for other processes, such as the remineralization of nutrients, and organic matter dynamics.},
  language  = {en}
}
@article{KleebergHupferGustetal.2013,
  author    = {Kleeberg, Andreas and Hupfer, Michael and Gust, Giselher and Salka, Ivette and Pohlmann, Kirsten and Grossart, Hans-Peter},
  title     = {Intermittent riverine resuspension effects on phosphorus transformations and heterotrophic bacteria},
  series = {Limnology and oceanography},
  volume    = {58},
  journal   = {Limnology and oceanography},
  number    = {2},
  publisher = {Wiley},
  address   = {Waco},
  issn      = {0024-3590},
  doi       = {10.4319/lo.2013.58.2.0635},
  pages     = {635 -- 652},
  year      = {2013},
  abstract  = {Intermittent riverine resuspension (IRR), a common phenomenon, was applied to investigate its effects on sedimentary resources availability and bacteria in the water column. This lab experiment used organic-rich lowland river sediment in a newly designed erosion chamber, the Benthic Water Column Simulator, generating well-defined ratios of shear velocity u* to turbulence intensity. Eight consecutive resuspension events, 1-8, were initiated at u* = 1.1 cm s(-1). Sedimentary and phosphorus entrainment decreased from 20.4 g m(-2) h(-1) and 111.6 mg m(-2) h(-1) at event 1 to 1.31 g m(-2) h(-1) and 18.7 mg m(-2) h(-1) at event 8, suggesting an exhaustion of particulate and dissolved sediment constituents. Entrainment of particle-associated (PA) bacteria (132.7 x 10(9)-251.1 x 10(9) cells m(-2) h(-1)) was strongly correlated to that of particles. Free-living (FL) bacteria (-27.6 x 10(9)-36.4 x 10(9) cells m(-2) h(-1)) were fractionally entrained. Numbers of PA bacteria remained low after each event, whereas those of FL bacteria strongly increased 5-15 h after an event because of growth due to increased availability of dissolved organic carbon and inorganic nutrients following each event. FL bacteria community structure also changed during IRR. The systematic changes over consecutive IRR cycles show a strong effect in all considered parameters that elude the typical single-event, steady-state experiments. IRR should thus be considered in two respects: experimental protocols on riverine water quality should be revised. In ecosystem modeling, IRR should be considered to better predict extent and effect of resuspension. Only IRR adequately reflects the natural interplay between hydrodynamics and organisms in rivers.},
  language  = {en}
}
@article{SalkaWurzbacherGarciaetal.2014,
  author    = {Salka, Ivette and Wurzbacher, Christian and Garcia, Sarahi L. and Labrenz, Matthias and Juergens, Klaus and Grossart, Hans-Peter},
  title     = {Distribution of acI-Actinorhodopsin genes in Baltic Sea salinity gradients indicates adaptation of facultative freshwater photoheterotrophs to brackish waters},
  series = {Environmental microbiology},
  volume    = {16},
  journal   = {Environmental microbiology},
  number    = {2},
  publisher = {Wiley-Blackwell},
  address   = {Hoboken},
  issn      = {1462-2912},
  pages     = {586 -- 597},
  year      = {2014},
  language  = {en}
}
@article{CornoSalkaPohlmannetal.2015,
  author    = {Corno, Gianluca and Salka, Ivette and Pohlmann, Kirsten and Hall, Alex R. and Grossart, Hans-Peter},
  title     = {Interspecific interactions drive chitin and cellulose degradation by aquatic microorganisms},
  series = {Aquatic microbial ecology : international journal},
  volume    = {76},
  journal   = {Aquatic microbial ecology : international journal},
  number    = {1},
  publisher = {Institute of Mathematical Statistics},
  address   = {Oldendorf Luhe},
  issn      = {0948-3055},
  doi       = {10.3354/ame01765},
  pages     = {27 -- +},
  year      = {2015},
  abstract  = {Complex biopolymers (BPs) such as chitin and cellulose provide the majority of organic carbon in aquatic ecosystems, but the mechanisms by which communities of bacteria in natural systems exploit them are unclear. Previous degradation experiments in artificial systems predominantly used microcosms containing a single bacterial species, neglecting effects of interspecific interactions. By constructing simplified aquatic microbial communities, we tested how the addition of other bacterial species, of a nanoflagellate protist capable of consuming bacteria, or of both, affect utilization of BPs. Surprisingly, total abundance of resident bacteria in mixed communities increased upon addition of the protist. Concomitantly, bacteria shifted from free-living to aggregated morphotypes that seemed to promote utilization of BPs. In our model system, these interactions significantly increased productivity in terms of overall bacterial numbers and carbon transfer efficiency. This indicates that interactions on microbial aggregates may be crucial for chitin and cellulose degradation. We therefore suggest that interspecific microbial interactions must be considered when attempting to model the turnover of the vast pool of complex biopolymers in aquatic ecosystems.},
  language  = {en}
}
@article{CepakovaHrouzekZiskovaetal.2016,
  author    = {Cepakova, Zuzana and Hrouzek, Pavel and Ziskova, Eva and Nuyanzina-Boldareva, Ekaterina and Sorf, Michal and Kozlikova-Zapomelova, Eliska and Salka, Ivette and Grossart, Hans-Peter and Koblizek, Michal},
  title     = {High turnover rates of aerobic anoxygenic phototrophs in European freshwater lakes},
  series = {Environmental microbiology},
  volume    = {18},
  journal   = {Environmental microbiology},
  publisher = {Wiley-Blackwell},
  address   = {Hoboken},
  issn      = {1462-2912},
  doi       = {10.1111/1462-2920.13475},
  pages     = {5063 -- 5071},
  year      = {2016},
  abstract  = {Aerobic Anoxygenic Phototrophic (AAP) bacteria are bacteriochlorophyll (BChl) a -containing organisms which use light energy to supplement their predominantly heterotrophic metabolism. Here, we investigated mortality and growth rates of AAP bacteria in three different freshwater lakes in Central Europe: the mountain lake Plesne, the oligo-mesotrophic Lake Stechlin and the forest pond Huntov. The mortality of AAP bacteria was estimated from diel changes of BChl a fluorescence. Net and gross growth rates were calculated from the increases in AAP cell numbers. The gross growth rates of AAP bacteria ranged from 0.38 to 5.6 d(-1), with the highest values observed during summer months. Simultaneously, the rapidly growing AAP cells have to cope with an intense grazing pressure by both zooplankton and protists. The presented results document that during the day, gross growth usually surpased mortality. Our results indicate that AAP bacteria utilize light energy under natural conditions to maintain rapid growth rates, which are balanced by a generally intense grazing pressure.},
  language  = {en}
}