Nassula (200µ) (All images are from video frames.)

Jellybean shaped Nassula is from an ancient line of ciliates, possibly going back to a time when cyanobacteria were a major food source for early eukaryotic cells. Nassula continues this ancient diet today by engulfing strands of Oscillatoria. Its food habits make it one of the most colorful ciliates, due to Oscillatoria fragments in various stages of digestion.

Feeding

The bean-shaped cell is slightly flatter on its ventral side, the mouth side. It glides along the strand feeling until it comes to an end. Then, positioning its mouth over the end of the filament, Nassula begins drawing in the strand. The ribbed mouth-basket fits snugly around the strand, which glides smoothly into the cell. As the flexible strand slides around the cell periphery, Nassula is stretched into a pancake shape. The strand may make two full turns around the cell before breaking into sections, allowing Nassula to resume its jellybean shape and begin the process of digestion. But digestion in Nassula must differ from normal ciliate phagocytosis whereby the food item is engulfed in an extension of the plasma membrane, forming a food vacuole. Here, a long chain of cells is engulfed and then broken into fragments that somehow become incorporated into food vacuoles. How this is accomplished is an excellent question for research.

Nassula showing mouth basket

Nassula engulfing strand of Oscillatoria

Culturing

Having not seen one in years, I discovered Nassula in a clump of Oscillatoria collected from a temporary stream. Using an eyedropper drawn out to a one millimeter diameter tip, I transferred four Nassula individuals, along with a clump of Oscillatoria, to a petri dish about half filled with water from the stream. By day four all of the Oscillatoria had been eaten and there were several hundred hungry Nassula awaiting another hand-out. Several hours after their next feeding many of the individuals underwent fission.

Nassula population increasing

Nassula, food vacuoles

Encystment

We have collected Nassula from desert rain pools that dry for 11 months of the year during which time they experience temperatures ranging from a cooking 120 F to freezing. Survival in these environments requires a resistant cyst stage. To study encystment, try allowing a culture of Nassula to dry out. Look for changes in the cells as their environment changes and ask the following questions: Is a muddy bottom necessary (it could prolong the period of gradual drying, allowing time for the cellular changes associated with encystment)? Following encystment is freezing or drying a requirement for excystment (some organisms use this strategy to adjust their life cycle to seasonal wet and dry cycles)

"I ate the whole thing!"