RESUMEN
A new bacteriophage Tt91 of larger size and broad lytical spectrum has been isolated from soil to widen the possibility to study new Bacillus thuringiensis strains. The Tt91 bacteriophage was shown to perform the intravariant transduction and, thus, can be used for genetic mapping. The ultrastructural analysis made it possible to refer bacteriophage Tt91 to morphotype A1 and showed similarity of Tt91 morphological structure to the one of CP-group bacteriophages. The performed comparative analysis of phage-specific proteins has confirmed a possible relation of the bacteriophages and revealed the differences between them. The data on the resistance of Tt91 DNA to majority of site-specific restriction endonucleases (17 out of 18 tested) and on DNA melting in the wide interval of temperatures suggests the presence of possible anomalies in the Tt91 DNA.