The involvement of Microbial Epiphytes in Uptake Measurements with the Giant-celled Alga Chara australis

Abstract

The giant-celled algae Chara and Nitella have been used extensively in studies of the transport of ions and other solutes. Before this report, uptake measurements were made without a detailed consideration of the effects of microbial epiphytes living on the external surface of the algal cell wall. Examination of the cell walls of Chara and Nitella with the scanning electron microscope revealed the presence of an often dense microflora consisting of diatoms, many types of bacteria, and even fungi. The contribution of this microflora to uptake measurements made with radiotracers was estimated by using isolated Chara cell wall cylinders internally filled with a silicone compound. For the Chara tested by us, the microflora was shown to make a substantial contribution to the uptake of urea, uric acid and glycine measured for untreated internodes. It was shown that, by briefly soaking Chara internodes in an artificial pond water, pH 8.5, containing 3 mM EGTA and then wiping their surfaces with a Kimwipe (a lint-free paper tissue), the microbial epiphytes can be quickly and simply removed. This treatment could be very useful in radiotracer studies of giant-celled algae in which the activity of the surface microflora complicates measurements of solute uptake.