Four small DNA-containing bacillus phages, M2, Nf, φ29, and φ15, could be classified into two groups according to their response to anti-phage sera and other experimental results; M2 and Nf belong to one group, and φ29 and φ15 to another group. The presence of 6-(p-hydroxyphenylazo) uracil has no effect on the production of these phages, but nalidixic acid inhibits their growth significantly as reported for φ29.
