A small population of planktonic Flavobacteria with disproportionally high growth during the spring phytoplankton bloom in a prealpine lake

Abstract

Bacterioplankton growth in temperate Lake Zurich (Switzerland) was studied during the spring phytoplankton bloom by in situ techniques and short-term dilution bioassays. A peak of chlorophyll a (Chl a) concentrations was followed by a rise of bacterial cell numbers and leucine assimilation rates, of the proportions of cells incorporating 5-bromo-2-deoxyuridine (BrdU), and of community net growth rates in dilution cultures. Incorporation of BrdU was low in Betaproteobacteria (2 +/- 1%), indicating that these bacteria did not incorporate the tracer. Pronounced growth of Betaproteobacteria in the enrichments was only observed after the decline of the phytoplankton bloom. An initial peak in the proportions of BrdU-positive Actinobacteria (30%) preceded a distinct rise of their cell numbers during the period of the Chl a maximum. Cytophaga-Flavobacteria (CF) changed little in numbers, but featured high proportions of BrdU-positive cells (28 +/- 12%). Moreover, CF represented > 90% of all newly formed cells in dilution cultures before and during the phytoplankton bloom. One phylogenetic lineage of cultivable Flavobacteria (FLAV2) represented a small (0.5-1%) but highly active population in lake plankton. The growth rates of FLAV2 in dilution cultures doubled during the period of the Chl a maximum, indicating stimulation by phytoplankton exudates. Thus, CF, and specifically Flavobacteria, appeared to be substantially more important for carbon transfer in Lake Zurich spring bacterioplankton than was suggested by their standing stocks. The high in situ growth potential of these bacteria might have been counterbalanced by top-down control.

Quantitative dominance of seasonally persistent filamentous cyanobacteria (Planktothrix rubescens) in the microbial assemblages of a temperate lake

“…This was revealed by two independent approaches, the precise measurement of filament biovolumes and lengths ( Fig. 1D,E ;Zeder et al 2010) and by weighting the biomass estimates by the respective water volumes of the different depth layers (Fig. 4A).…”

“…The typically observed patterns, e.g., during phytoplankton spring blooms, are an increase of dissolved organic carbon and of bacterial cell numbers and activity (Simon et al 1998) during or after the maximum concentrations of chlorophyll a (Chl a) and a subsequent formation of macroscopic organic aggregates (due to the agglutination of senescent algae) colonized by bacteria that differ from single-celled planktonic taxa (Grossart et al 1997;Schweitzer et al 2001). Such transient phytoplankton blooms are often accompanied by pronounced changes in microbial community composition, e.g., a disproportionate rise of bacteria affiliated with Flavobacteria (Zeder et al 2009), Betaproteobacteria (Salcher et al 2008), or Actinobacteria (Salcher et al 2010). By contrast, considerably less is known about the coexistence of bacteria with phytoplankton groups that are seasonally more persistent (Š imek et al 2008).…”

“…Sampling started with the increasing growth of metalimnetic P. rubescens at the beginning of stable summer stratification and ended after the onset of autumnal mixis, i.e., after the first entrainment of cyanobacterial filaments in the upper water body. Three phyla of heterotrophic bacteria were distinguished that typically respond to phytoplankton bloom situations (Zeder et al 2009;Salcher et al 2010). In addition, the fine-scale taxonomic differences in the bacterial assemblages within, above, and below the zone of maximal P. rubescens densities were analyzed in detail on one occasion.…”

“…The interactions between heterotrophic bacteria and primary producers in freshwaters have mainly been investigated in the context of artificially induced (Riemann and Søndergaard 1986) or natural (Zeder et al 2009) shortlived blooms of prokaryotic and eukaryotic phytoplankton species. The typically observed patterns, e.g., during phytoplankton spring blooms, are an increase of dissolved organic carbon and of bacterial cell numbers and activity (Simon et al 1998) during or after the maximum concentrations of chlorophyll a (Chl a) and a subsequent formation of macroscopic organic aggregates (due to the agglutination of senescent algae) colonized by bacteria that differ from single-celled planktonic taxa (Grossart et al 1997;Schweitzer et al 2001).…”

Climate‐related changes of soil characteristics affect bacterial community composition and function of high altitude and latitude lakes

“…2011). In turn, bacterial communities have been shown to respond quickly to variation in substrate availability and concentration, often favouring opportunistic bacteria such as members of Betaproteobacteria (Burkert et al ., 2003; Šimek et al ., 2005; Hornák et al ., 2006; Posch et al ., 2007) or Bacteroidetes (Cottrell & Kirchman, 2000; Battin et al ., 2001; Eiler et al ., 2003; Zeder et al ., 2009). Besides the critical role of heterotrophic bacteria in processing soil‐derived organic matter in inland waters, knowledge on covarying factors, such as the release from nutrient limitation during pulses of soil run off in high altitude and latitude lakes remains limited (Pérez & Sommaruga, 2006).…”