Suttle, C.A., A.M. Chan and I. Kaczmarska. 1994. Isolation and initial characterization of a lytic mycoplasmalike organism which infects a marine diatom (Navicula pulchripora). Abstracts American Society Microbiology, Las Vegas, NV, May 1994.

A lytic pathogen which infects a marine diatom was isolated from the coastal waters of Texas. The agent is filterable through a 0.2 µm pore-size filter, is heat labile (56 C) and sensitive to chloroform and cyanide. It can be propagated indefinitely by transferring a small inoculum from an infected culture into an uninfected culture. Introduction of the pathogen resulted in complete lysis of diatom cultures within a few days. The concentration of the lytic agent in culture lysate was determined by most-probable number assay to be 19600 ml^-1 (95 % C.I. 10300 to 37200 ml^-1). The pathogen was unable to infect seven other pennate and centric diatoms that were tested. Transmission electron microscopy was used to observe the infection process. After infection, but before cell lysis, membrane-bound ellipsoid and spherical bodies were observed in the cytoplasm of degenerating cells. Similar inclusions were not present in uninfected cells. The morphology of these inclusions was consistent with mycoplasmalike organisms and suggests that mollicutes may be pathogens of unicellular algae. Furthermore, as the pathogen and host are easily culturable they should be an excellent model system for studying the biology of the mollicute infection process.