Experimental Studies to Modify the Number of Endocytic Bacteria in Cryptomonas Strain SAG 2580 (Cryptophyceae) and their Lysis by Bacteriophages

Abstract

Cryptomonas strain SAG 2580 contains three forms of endocytic bacteria (Schnepf & Melkonian 1990), those within peribacterial vacuoles as well as free (not surrounded by a membrane) ones in the ground cytoplasm. Some of the latter are crowded with virions. They do not completely lyse in the cytoplasm but are digested in lysosomes. In order to investigate the relationships between cryptomonads and bacteria and between the different forms of bacteria, cells at various growth conditions were studied by electron microscopy. In general, the total number of bacteria per cell is fairly constant. It is, however, low after treatment with 2 mg · I-1 gentamycin and high in the stationary phase, mainly because the number of free bacteria without virions is then increased. Only the bacteria within peribacterial vacuoles are able to grow and to divide. It is concluded that they also contain virus genomes and represent a stock from which the other forms develop, controlled by the host. The lysis of the bacteria could not be increased by a temperature shock. Attempts to remove the endocytic bacteria failed. The cryptomonads did not grow in the absence of extracellular bacteria.