Molecular criteria for distinguishing bacillaris and Z strains of Euglena gracilis

The purpose of this work is to allow the distinction between Z and bacillaris types of Euglena gracilis using reliable criteria. By hybridization with radioactive probes, the restriction patterns of nuclear ribosomal operons and of chloroplast ribosomal operons were compared between strains. Clear differences between the bacillaris and Z strains are evident. The results show that one strain hitherto considered as a Z strain belongs to the bacillaris type. Ultraviolet irradiation reveals that chloroplast mutability of Z strains does not depend on the number of chloroplast ribosomal operons. In addition, comparisons between bleaching curves and rates of greening of the colonies do not provide a reliable basis for distinguishing between the Euglena gracilis types. We propose therefore to distinguish Z and bacillaris types using molecular criteria, mainly nuclear ribosomal DNA patterns.