Identification in situ and dynamics of bacteria on limnetic organic aggregates (lake snow)

Abstract

Microbial assemblages on large organic aggregates (lake snow) of Lake Constance, Germany, were analyzed with rRNA-directed fluorescent oligonucleotide probes specific for the domain Bacteria and the ␣-, ␤-, and ␥-subclasses of the class Proteobacteria. Lake snow aggregates were either collected in situ by SCUBA diving or in a sediment trap at 50 m or formed of natural lake water incubated in rolling cylinders under simulated in situ conditions. For the latter aggregates, the time course of the microbial colonization was also examined. The natural aggregates and those made in rolling cylinders were composed of the particulate organic material present in the lake and thus reflected the composition of the ambient plankton community. All types of lake snow aggregates examined were heavily colonized by microbial cells and harbored between 0.5 ؋ 10 6 and >2 ؋ 10 6 cells aggregate ؊1. Between 55 and 100% of the microbial cells stained with 4,6-diamidino-2-phenylindole (DAPI) could be visualized with the domain Bacteria-specific probe. In most samples, ␤-subclass proteobacteria dominated the microbial community, constituting 27 to 42% of total cells as counted by DAPI staining, irrespective of the composition of the aggregates. During the time course experiments with the laboratory-made aggregates, the fraction of ␤-subclass proteobacteria usually increased over time. Except for a few samples, ␣and ␥-subclass proteobacteria were far less abundant than ␤-subclass proteobacteria, constituting 11 to 25 and 9 to 33% of total cells, respectively. Therefore, we assume that a specific aggregate-adapted microbial community was established on the aggregates. Because the compositions of the microbial assemblages on natural and laboratory-made aggregates were similar, we conclude that aggregates made in rolling cylinders are a good model system with which to examine the formation and microbial colonization of macroscopic organic aggregates.

Bacterial activity and community composition in stream water and biofilm from an urban river determined by fluorescent in situ hybridization and DGGE analysis

“…During the di¡erent months sampled, bacteria on polycarbonate slides were dominated by the L subclass of Proteobacteria. This group of bacteria has been described as the most morphologically diverse group within bio¢lms [5], and a dominant group in fresh water systems such as oligotrophic lakes, drinking water bio¢lms [29,36,37], river snow [26] and eutrophic rivers [9,30]. It seems to be a common feature of most aquatic environments.…”

Regulation of bacterial biomass and community structure by metazoan and protozoan predation

“…This is not surprising, since detrital particles constitute a special microhabitat, probably with higher substrate supply and lower grazing pressure (Caron 1987;Kirchman 1993). It has been shown already in marine (e.g., DeLong et al 1993;Rath et al 1998), estuarine (Crump et al 1999), and limnetic (Weiss et al 1996) habitats that particles (marine or lake ''snow'') harbor different bacterial communities.…”

Bacterial production and growth efficiencies: Direct measurements on riverine aggregates

“…The samples were then fixed in 40 l of fresh paraformaldehyde (4%) for 4 h at 4ЊC. Percentages of Archaea and Bacteria, members of the ␣-, ␤-, and ␥-subclass of Proteobacteria, of the Cytophaga-flexibacterium bacteroides cluster (Cytophaga) and of sulfate-reducing bacteria were examined by in situ hybridization with 16S rRNA targeted fluorescent oligonucleotide probes according to Weiss et al (1996). Exact sequences of oligonucleotide probes to detect Archaea, Bacteria, ␣-, ␤-, and ␥-Proteobacteria, as well as Cytophaga are given by Amann et al (1995), whereas those of sulfate-reducing bacteria are given by Amann et al (1990;SRB 385) and Rabus et al (1996;SRB dB).…”