Members of a Readily Enriched β-Proteobacterial Clade Are Common in Surface Waters of a Humic Lake

Abstract

Humic lakes are systems often characterized by irregular high input of dissolved organic carbon (DOC) from the catchment. We hypothesized that specific bacterial groups which rapidly respond to changes in DOC availability might form large populations in such habitats. Seasonal changes of microbial community composition were studied in two compartments of an artificially divided bog lake with contrasting DOC inputs. These changes were compared to community shifts induced during short-term enrichment experiments. Inocula from the two compartments were diluted 1:10 into water from the more DOC-rich compartment, and inorganic nutrients were added to avoid microbial N and P limitation. The dilutions were incubated for a period of 2 weeks. The microbial assemblages were analyzed by cloning and sequencing of 16S rRNA genes and by fluorescence in situ hybridization with specific oligonucleotide probes. ␤-Proteobacteria from a cosmopolitan freshwater lineage related to Polynucleobacter necessarius (beta II) were rapidly enriched in all treatments. In contrast, members of the class Actinobacteria did not respond to the enhanced availability of DOC by an immediate increase in growth rate, and their relative abundances declined during the incubations. In lake water members of the beta II clade seasonally constituted up to 50% of all microbes in the water column. Bacteria from this lineage annually formed a significantly higher fraction of the microbial community in the lake compartment with a higher allochthonous influx than in the other compartment. Actinobacteria represented a second numerically important bacterioplankton group, but without clear differences between the compartments. We suggest that the pelagic microbial community of the studied system harbors two major components with fundamentally different growth strategies.

Low Intraspecific Diversity in a Polynucleobacter Subcluster Population Numerically Dominating Bacterioplankton of a Freshwater Pond

“…To our knowledge, the absolute numerical dominance of a species-like bacterial population in a nonextreme aquatic habitat, as well as the occurrence of such a planktonic population with cell numbers of Ͼ1 ϫ 10 6 ml Ϫ1 , was not reported previously. Bacterial groups demonstrated to occur in nonextreme habitats with high relative numbers represented much broader phylogenetic groups (7,36). For instance, the wellinvestigated SAR11 cluster, which comprises up to 50% and, on average, 30% of bacterioplankton in marine surface waters (36), represents a broad phylogenetic group with a minimum 16S rRNA sequence similarity of 88.8% (PnecC, 98.5%).…”

“…We demonstrated by FISH the presence of free-living PnecC cells in the pelagic zone of a freshwater habitat. This indicates that many or all of the environmental PnecC sequences collected from the pelagic zones of freshwater habitats (7,10,11,21,27,50) originate from free-living cells; however, it is still not known if these cells represent completely free-living strains or facultative endosymbionts of ciliates. The numerically significant contribution of free-living stages of facultative endosymbionts or facultative parasites of protists (e.g., Legionella spp.)…”

Distinct and diverse anaerobic bacterial communities in boreal lakes dominated by candidate division OD1

“…Even though there are several studies addressing bacterial communities in humic lakes (for example, Lindströ m, 1998;Burkert et al, 2003;Kent et al, 2004), the microbial diversity and community composition of the suboxic hypolimnetic layers remain poorly explored and the few studies available are typically restricted to very specific questions, sediment communities, or are based on methods that provide little if any information on taxonomy (for example, Kleinsteuber et al, 2008;Lehours et al, 2009;Berdjeb et al, 2011;Taipale et al, 2011) or diversity (Bent et al, 2007). One exception is the recent study by Barberan and Casamayor (2011), which used observations from multiple lakes to demonstrate that microbial communities in the hypolimnia are distinct from those in the epilimnia.…”

Bacterial degradation of dissolved organic matter released by Planktothrix agardhii (Cyanobacteria)

“…The large distribution of Betaproteobacteria in freshwater environments is usually associated to their high capacity of adaptation to different environments, and fast response of growth (Burkert et al, 2003;Šimek et al, 2005). Langenheder et al (2004) suggested that Gammaproteobacteria may be fast growing opportunists dominating at high nutrient levels, whereas in low nutrient concentrations they may be out-competed by Alphaproteobacteria.…”