The differences between Underwood et al [35] on the one hand and our study as well as the study of Deakin and coworkers [34] on the other hand may be explained by differences in experimental conditions, such as the medium used. However, we observed no difference in cytotoxicity between supernatant derived from wild type or spo0A mutant cells when they were grown in BHIS, a medium nearly identical to that used previously (data not shown). Alternatively, the differences could indicate integration of the group II intron at more than one location in the chromosome in the strain used in Underwood et al [35] . In the absence of a complementation experiment and/or Southern blot data, this remains to be established.