Article Figures & Data
Figures
- FIG. 1.
Time course changes in bacterial abundance and biomass in different size fractionation treatments of <0.8 μm, <5 μm, and UNF reservoir water collected and exposed in dialysis bags at the dam area of the reservoir compared to the changes in the same <0.8-μm and <5-μm treatments but incubated in bottles or transplanted upstream to the middle and river inflow of the reservoir and incubated there in dialysis bags. Values are means for two replicate treatments. Error values are not shown to allow for a better visualization of the changes.
- FIG. 2.
Time course changes in bacterial production (Bact. prod.) and total protistan bacterivory in different size fractionation treatments of reservoir water collected at the dam area and incubated in bottles or in dialysis bags at the dam, middle, and river parts of the reservoir (for more details, see the Fig. 1 legend). Values are means for two replicate treatments. Note that “total protistan grazing” refers only to HNF bacterivory in all but the unfiltered treatment incubated at the dam site (DAM UNF), where ∼20% of total grazing was caused by the ciliates present in the sample (data not shown).
- FIG. 3.
Negative image of the bacterial 16S rRNA gene fragments separated by DGGE from the different size fractionation treatments of <0.8 μm and <5 μm at time zero compared to changes in banding patterns of samples incubated in bottles and in dialysis bags at the dam, middle, and river parts of the reservoir at the end of the incubation.
- FIG. 4.
Time course changes in the phylogenetic composition of the bacterioplankton community in different size fractionation treatments of reservoir water collected at the dam area and incubated in bottles or in dialysis bags at the dam, middle, and river parts of the reservoir (for more details, see the Fig. 1 legend). Shown are proportions of total FISH detection rates by the general bacterial probe EUB338, β-proteobacteria (BET42a), and the cells detected by the probe R-BT065, γ-proteobacteria (GAM42a), the Cytophaga/Flavobacterium group (CF319a), and the Actinobacteria group (HGC69a). Values are means of two replicate treatments.
- FIG. 5.
Time course changes in the proportions of bacteria with HNA content related to total DAPI-stained bacteria in different size fractionation treatments of reservoir water collected at the dam area and incubated in bottles or in dialysis bags at the dam, middle, and river parts of the reservoir (for more details, see the Fig. 1 legend). Values are means for two replicate treatments.
- FIG. 6.
Relationships between the proportions of bacteria with HNA content related to total DAPI-stained bacteria and proportions of probe-defined bacterial subpopulations with data pooled from all treatments (n = 45). (A) EUB338-detectable cells; (B) BET42a-detectable cells; (C) R-BT065-detectable cells. Full lines depict linear regressions for all data, and the r2 value shows the coefficient of determination of the regressions. In C, the open symbols are those from bacterivore-free treatments only (n = 20) fitted with the dashed regression line; closed symbols are for treatments with the presence of grazers. All regressions are significant (P < 0.0001).
Tables
- TABLE 1.
Net doubling times of ungrazed bacterioplankton and different bacterial subgroupsa
Incubation site Doubling time (h) Interval (h) Bacterioplankton R-BT065 BET42a GAM42a CF319a HGC69a Dam 20** 8 13** 11 23* 23* 0-48 Bottle 42 19 29 60 32 35 0-48 Middle 20** 9 13 8 12* 18 0-48 River 16 9 11 10 14 12 24-72 ↵a Shown are net doubling times of ungrazed bacterioplankton and different bacterial subgroups in the predator-free treatments (<8 μm) exposed at the dam area in dialysis bags (dam) and bottles compared to those transplanted and incubated in dialysis bags in the middle and river inflow parts of the reservoir. The values are means for two duplicate treatments. Rates were calculated for intervals with exponential growth using nonlinear fit of the duplicated data followed by testing significant differences in doubling times of the bacteria targeted by the R-BT065 probe compared to other bacterial groups. *, P < 0.05; **, P < 0.01.
- TABLE 2.
Two-way ANOVA used to test for differences in BCC between the dam, middle, and river incubations throughout all experimental variants and different time intervalsa
Probe Bottom-up manipulationb (F value) Top-down manipulationc (F value) 24 h 48 h 72 h 96 h 24 h 48 h 72 h 96 h BET42a 3.16 0.35 1.49 0.18 0.22 0.72 0.65 1.13 R-BT065 15.3** 80.5*** 6.12* 0.48 29.4*** 583*** 18.8** 6.24* GAM42a 0.27 0.36 1.79 3.86 6.15* 11.3* 2.32 2.12 CF319a 0.66 27.1** 8.45* 0.96 3.07 0.09 0.02 0.01 HGC69a 1.09 2.94 0.61 2.28 10.5* 43.3*** 6.4* 6.2* ↵a We tested the differences in the relative contributions (as a percentage of total DAPI-stained bacteria) of five different phylogenetic groups of bacteria targeted by the probes BET42a, R-BT065, GAM42a, CF319a, and HGC69a induced by transplanting the samples from the dam area upstream to the middle and river areas and by manipulating top-down control via size fractionation of water samples. The significant differences are in boldface type. *, P < 0.05; **, P < 0.01; ***, P < 0.001.
↵b Dam samples transplanted to the middle and river parts.
↵c Effects of distinct grazing pressures when bacterivore-free treatments are compared to bacterivore-enhanced treatments.
- TABLE 3.
Correlation relationships between the proportion of HNA cells within the bacterial assemblages compared to HNF and bacterioplankton parameters and the proportions of FISH-detected subgroups of bacteria across all experimental treatmentsa
Parameter Correlation coefficient (r) Significance (P) HNF abundance 0.045 0.8302 Total HNF grazing 0.063 0.7641 Bacterial abundance 0.846 <0.0001 Bacterial production 0.715 <0.0001 Bacterial biomass 0.845 <0.0001 Bacterial mean cell volume 0.813 <0.0001 % EUB338 0.643 <0.0001 % BET42a 0.814 <0.0001 % R-BT065 0.792 <0.0001 % GAM42a 0.585 <0.0001 % CF319a 0.461 0.0014 % HGC69a −0.016 0.2912 ↵a For calculations, the proportions of HNA bacteria and FISH-detected bacterial subgroups were expressed as a percentage of total DAPI stained cells. For all analyses, n = 45, except for those with HNF abundance and grazing (n = 25). Significant relationships (P < 0.01) are shown in boldface type.
- TABLE 4.
Correlation relationships between the proportions of β-Proteobacteria (the BET42a probe-detected cells) and of the subcluster of β-Proteobacteria (R-BT065 probe-detected cells) as components of the bacterial community versus basic bacterioplankton parameters throughout all treatmentsa
Parameter % BET42a % R-BT065 Correlation coefficient (r) Significance (P) Correlation coefficient (r) Significance (P) Bacterial abundance 0.615 <0.0001 0.810 <0.0001 Bacterial biomass 0.587 <0.0001 0.753 <0.0001 Bacterial mean cell volume 0.661 <0.0001 0.575 <0.0001 Bacterial production 0.529 0.0004 0.546 0.0002 ↵a For calculations, the proportions of FISH-detected bacterial subgroups were expressed as a percentage of total DAPI-stained bacteria. For all analyses, n = 45.
