Meeting Abstract
The rotifer, Brachionus plicatilis, ingests particulate foods ranging from ∼0.4 – 10 μm in size. Although clearance rates of small particles (< 1 μm) are low, bacteriophages (< 0.05 μm) are abundant in seawater (to 108/mL) and represent a potential food source for rotifers and other planktonic invertebrates. We incubated amictic females of B. plicatilis with dichlorotriazinylamino fluorescein (DTAF)-labeled bacteriophages (108/mL) or 900 pM DTAF in 0.2 μm-filtered seawater; the DTAF concentrations were equal in both treatments. After a 5-h incubation, the label in rotifers was detected using epi-illumination or confocal microscopy. The fluorescence of rotifers was greater in the DTAF-bacteriophage treatments than the unbound DTAF treatments; rotifers not exposed to the label revealed the lowest fluorescence. The distribution of the label within rotifers was similar for both experimental treatments. The greatest fluorescence was detected within the stomach and steadily decreased with increasing distance from this organ. In areas outside of the stomach, fluorescence was primarily diffuse and of lower intensity, but a small number of vesicles (4-5 μm) containing the label was detected. In the DTAF-bacteriophage treatments, stomach cells contained an abundance of fluorescent vesicles. The appearance of label in vesicles is consistent with earlier reports of pinocytotic uptake of materials by stomach cells. We hypothesize that bacteriophages and unbound DTAF entered the digestive system within an ingested flow of seawater. These findings indicate that bacteriophages in aquatic systems represent a previously unrecognized food source for planktonic invertebrates and their larvae.
