Dynamics and bacterial colonization of microaggregates in a large mesotrophic lake

Abstract

We studied the occurrence and dynamics of transparent exopolymer particles (TEP) and 4'-6'-diamidino-2-phenylindole (DAPI)-stained microaggregates (MA) and the bacterial colonization of the latter by fluorescence in situ hybridization with rRNA-targeted oligonucleotides in Lake Constance, Germany, from June to December 1996. MA were categorized into the size classes 8 to 20, 20 to 60 and > 60 µm. Total abundance of TEP varied between 71 and 2554 ml -1 and that of MA between 310 and 1526 ml -1 with the largest proportion in the size class 8 to 20 µm (140 to 959 ml -1). Numbers of TEP and of MA > 60 µm, never exceeding 100 ml -1 , decreased with depth and were correlated to the biomass of total phytoplankton, diatoms, chrysophytes and dinoflagellates. Numbers of the smaller-sized MA did not systematically decrease with depth. Four types of DAPI-stained MA were identified: aggregates composed of bacterial and of cyanobacterial colonies, aggregates fluorescing yellow (DAPI yellow particles), and phytoplankton and zooplankton fragments fluorescing faintly blue after DAPI staining. The latter and DAPI yellow particles were most abundant. The majority of MA was densely colonized by bacteria. At least 20% of the DAPI-stainable cells were detected by the Bacteria-specific probe EUB338 and a mean between 44 and 56% of the various types of MA. β-Proteobacteria dominated aggregates composed of remains of diatoms and often also on fragments. On DAPI yellow particles bacteria of this phylogenetic lineage and the Cytophaga/Flavobacteria cluster were equally abundant. γ-Proteobacteria usually constituted only minor proportions except on fragments of Dinobryon spp. and of zooplankton origin on which they constituted up to 62% of the DAPI-stainable cells. α-Proteobacteria were not detected at all. Together, all group-specific probes constituted > 95% of the bacteria detected by the EUB338 probe on MA except for bacterial aggregates on which only 59% were detected. The different spatio-temporal dynamics of TEP and MA and the bacterial colonization of the latter suggested that TEP and MA > 60 µm were early decomposition products mainly of diatoms and other algae whereas smaller MA were more degraded stages of detrital particulate organic matter.KEY WORDS: Microaggregates · Transparent exopolymer particles · Bacteria · In situ hybridization · Lake ConstanceResale or republication not permitted without written consent of the publisher

Seasonal patterns of the bacterioplankton community composition in a large mesotrophic lake

“…This notion is consistent with comparable studies in other freshwater systems including lakes, microscopic and macroscopic limnetic aggregates, and river biofilms (Grossart & Simon 1998, Pernthaler et al 1998, 2imek et al 1999, Brümmer et al 2000, Brachvogel et al 2001. Despite their great significance, limited information is available on the relative distribution of specific populations of β-Proteobacteria in lacustrine environments.…”

“…Schweitzer et al (2001) and Knoll et al (2001) experimentally examined the temporal succession of α-and β-Proteobacteria on lake snow aggregates and precursor microaggregates in Lake Constance, and found within the initial days high, but thereafter decreasing, proportions of α-Proteobacteria. On natural microaggregates in this lake, α-Proteobacteria were absent, supporting the idea that microaggregates represent particulate organic matter depleted greatly of labile organic matter (Brachvogel et al 2001). Hence, there is some evidence that limnetic α-Proteobacteria comprise bacteria which prefer rather labile organic matter, although more studies need be carried out to shed more light on the specific properties of members of this subclass of Proteobacteria.…”

Organic-Aggregate-Attached Bacteria in Aquatic Ecosystems: Abundance, Diversity, Community Dynamics and Function

“…The bacterial communities on lake snow aggregates in this lake have been intensively studied. Using FISH with rRNA-targeted oligonucleotides, Brachvogel et al (2001) found that -proteobacteria and Cytophaga/Flavobacteria dominated the bacterial community on microaggregates in Lake Constance, constituting 8 to 78% of the DAPI-stainable cells, which equals 14 to 82% of Bacteria. In contrast, -proteobacteria was not detected at all.…”

“…And -proteobacteria usually constituted only minor proportions except on zooplankton debris and on phytodetrital aggregates composed of Dinobryon spp. (Brachvogel et al 2001). …”

A procedure for establishing an axenic culture of the diatom Synedra acus subsp. radians (Kütz.) Skabibitsch. from Lake Baikal

“…Heterotrophic bacteria associated with diatoms and actively developing in most of their cultures are represented by different phylotypes. In particular, they include a-, b-, and g-proteobacteria, bacteroidetes, and actinobacteria (Brachvogel et al 2001;Knoll et al 2001;Schafer et al 2002;Makk et al 2003;Grossart et al 2005;Bruckner et al 2008;Zakharova et al 2010). Conventional approaches for obtaining of axenic diatom cultures employ physical and chemical methods for separating bacteria from diatoms, treatment with antibiotics, and isolation of individual diatom cells for monoclonal culturing (Spencer 1952;Brown and Bischoff 1962;Jones et al 1973;Daste et al 1983;Kobayashi et al 2003;Bruckner and Kroth 2009).…”