Article Figures & Data
Figures
- Fig. 1.
Influence of grazing by the bacterivorous flagellateOchromonas sp., inoculated on day 14 into C. acidovorans PX54 and Vibrio strain CB5 chemostat cultures (Flag1 experiment). (A) Total bacterial abundance and flagellate abundance. (B) Relative abundance of C. acidovorans PX54 determined either by immunofluorescence microscopy or by distinguishing colony types on agar plates. (C) Mean cell volume of the total bacterial community and percentage ofC. acidovorans PX54 cells larger than 10 μm (filamentous cells). (D) Biomasses of C. acidovorans PX54 and Vibrio strain CB5 populations in the flagellate-free and flagellate-controlled phases. Inoculation of the bacterivorous flagellate Ochromonas sp. is indicated by vertical lines.
- Fig. 2.
Influence of grazing by Ochromonas sp. on the model community consisting of C. acidovorans PX54 andVibrio strain CB5 (Flag2 experiment). (A) Bacterial abundance before and after inoculation with Vibrio strain CB5 and after introduction of the predator Ochromonas sp. and abundance of this flagellate. (B) Relative abundance of C. acidovorans PX54 and percentage of C. acidovorans PX54 cells larger than 10 μm (filamentous cells).
- Fig. 3.
(A and B) Microphotographs of C. acidovoransPX54 (green) and Vibrio strain CB5 (red) stained with fluorescently labelled antibodies (Flag1 experiment). (A) Before flagellate inoculation (day 8). (B) After flagellate inoculation (day 32). (C) Filamentous C. acidovorans PX54 cells grown in a flagellate-free batch culture (late exponential growth stage; cells stained with DAPI).
- Fig. 4.
Transient stage after introduction of the flagellate (on day 14) into a chemostat culture of C. acidovorans PX54 andVibrio strain CB5 (Flag1 experiment). In the beginning, the total bacterial numbers of both species decreased at similar rates, indicating nonselective grazing by the flagellate (lower panel). After day 16, Vibrio strain CB5 abundance continued to decrease but C. acidovorans PX54 abundance increased again and the relative species composition changed (upper panel).
- Fig. 5.
Size class distribution of Vibrio strain CB5 cells (left panels) and C. acidovorans PX54 cells (right panels) in corresponding chemostat samples from flagellate-free and flagellate-controlled phases (Flag1 experiment). Cells longer than 5 μm were pooled in one size class (>5 μm). To avoid distortion of size class distribution, measured cell lengths were corrected for size overestimation caused by cell staining with fluorescently labelled antibodies but not for size overestimation caused by DAPI staining (for details, see Materials and Methods).
- Fig. 6.
Influence of growth rate on the cell size and abundance of C. acidovorans PX54 and Vibrio strain CB5 in chemostat cultures (Dilut experiment). The change in dilution rate (growth rate) from 0.5 to 2.0 day−1 at day 10 simulated nonselective grazing similar to size-selective grazing byOchromonas sp. in flagellate-controlled phases of the Flag1 and Flag2 experiments.
- Fig. 7.
Four-step mechanism explaining the observed changes in relative species composition of binary chemostat cultures after introduction of the flagellate Ochromonas sp. Changes were caused by a combination of a grazing-controlled increase in the bacterial growth rate with the different growth rate-dependent elongation of cells of the two species and size-selective grazing by the flagellate.
Tables
- Table 1.
Overview of the three chemostat experiments
Expt Day of inoculation with: Day of: C. acidovoransPX54 Vibrio strain CB5 Ochromonassp. Increase in dilution rate End of expt Flag1 1 1 14 38 Flag2 1 15 34 62 Dilut 1 1 10 17 - Table 2.
Steady-state parameters of the flagellate-free and flagellate-controlled phases and parameters of the transient stages (after flagellate introduction until establishment of a new steady state) of the Flag1 and Flag2 chemostat experimenta
Parameter Flag1 expt Flag2 exptb Steady state Total bacterial abundance (106 ml−1) Without flagellates 10.3 ± 0.5 9.9 ± 0.4 With flagellates 0.34 ± 0.07 0.32 ± 0.06 Relative abundance of C. acidovorans PX54 (%) Without flagellates 6.5 ± 1.0 7.3 ± 0.4 With flagellates 67.0 ± 3.8 67.0 ± 1.1 Dynamic state (from transient stage; day−1) Rate of increase in flagellate no.b 0.51 1.15 Rate of bacterial cell no.cdecrease 0.65 1.14 ↵a Data on the flagellate-free phase of the Flag2 experiment represent the situation after inoculation withVibrio strain CB5. Steady-state parameters represent mean values ± standard deviations, and transient-stage values represent rates of exponential changes following flagellate inoculation.
↵b After inoculation with Vibriostrain CB5.
↵c After inoculation with the flagellate.
- Table 3.
Abundance of C. acidovorans PX54 andVibrio strain CB5 in the steady state of the flagellate-free phases of the three chemostat experimentsa
Expt Period (days) Mean abundance ± SD (106 ml−1) C. acidovoransPX54 Vibrio strain CB5 1 4–14 0.67 ± 0.08 9.63 ± 0.55 2b 2–15 0.68 ± 0.06 2c 20–34 0.72 ± 0.07 9.18 ± 0.51 3 6–10 1.00 ± 0.17 6.30 ± 0.13 ↵a In each experiment, the growth rate during the first phase was 0.5 day−1. In contrast to the other experiments, C. acidovorans PX54 grew initially in the Flag2 experiment without Vibrio strain CB5. This species was introduced at day 15 of the experiment, and 4 days later, a second steady state was established. Note that C. acidovorans PX54 abundance was not significantly (P > 0.1) influenced by the Vibrio strain CB5 population.
↵b Steady state before inoculation withVibrio strain CB5.
↵c Steady state after inoculation withVibrio strain CB5.
- Table 4.
Effect of growth phase on cell size in batch culture experimentsa
Bacterium Mean cell vol (μm3) % of cells >10 μm long μmax (h−1) Log phase Stationary phase C. acidovoransPX54 0.76 0.09 <1 0.17 Vibrio strain CB5 0.31 0.07 0.20 ↵a Mean cell volume in the late logarithmic and stationary phases (35 h after the end of the log phase), percentage of filamentous cells (late logarithmic phase), and the maximum growth rates of the two bacterial strains are shown. Batch cultures were grown in NSY medium at 15°C and 150 rpm.
